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BikerAfloat
01-08-2012, 07:20 PM
Hello All, here is my first post in what I hope will become a full build log. As mentioned in my Introduction (http://www.mycncuk.com/forums/new-member-introductions/4897-time-say-hello.html) I have one quite tough requirement a bit of steel machining and am building it with a view to making the plans available to others who are in the same boat as me, well not my Narrowboat, but you get what I mean :-)

Posted here are the drawings for the machine I have in mind for my use X=600mm (Apprx 400mm useable) Y=500mm (Apprx 300mm useable) and Z=350mm (Apprx 150mm useable). I hope this design is scaleable by adding longer rails and extra rail supports, that was certainly my intention. I have also allowed space where the drive nuts are to go upto 16mm leadscrews for the bigger machines, though I have seen 8'x4' machines with 12mm, to me it just doesn't look man enough.

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Build requirements are to use as many standard components as possible and any unique parts must be able to be made on a Pillar drill. I tried to design it so there had to be no sections that had to be cut to length, but I'm afraid I was only happy with a design that involved the 4 long X Axis beams to be of exact length. All other joints are on the main faces of the extrusions.

To repeat my self slightly My choice of components are governed by 3 factors 1) Cost, 2) Sizing, where possible they are Multiples of the 20mm of the sections I have used & 3) The need for nothing more complicated than a pillar drill.

The machine has come together quite chunky, but that to me is OK as I want to machine metal quite a bit of the time, say 10-20% and I have allowed the cutting area to extend over the rails at the front to give a solid base as I can for doing this.

I will put a Bill of Materials (BOM) on here soon, it's just a bit messy, as it was being constructed along side the drawing. I posted some of the major specs in my introduction, but a BOM will give a more complete story.

I may do a slight redraw to include the DumpsterCNC anti-backlash nuts as for the price I'm not sure my idea, to be posted soon can compete! I have tried to justify Ballscrews, but I wince at the prices and speed and accuracy are not my ultimate goals. I may change my mind of course once I start making stuff, but I am fairly confident I can retro fit them at a later date, without too much trouble. Mostly I want to get a machine going so I can start learning!!!!

I'm happy to provide more detailed views if you need them and really want to know if this design is viable.

Cheers,
Geoff.

JAZZCNC
01-08-2012, 07:56 PM
Hi Geoff,

I see some issues that will definitely affect it's ability to cut steel and will also affect performance in Aluminium.?

The tall gantry won't be any where near strong enough.!! While it's sat directly on the bearings the what looks like 45x45 uprights just won't handle the forces steel and aluminium will put on it.

The un-supported rails on the Z axis and to be honest the whole z axis design just won't be upto the job of steel or Ali.!

Don't know if your planning on putting any braces across the frame to support the bed.? But again to cut any hard material then extra support will be required.

Please don't take my comments has pulling the machine down just comments based on quite extensive work building router based machines that can cut hard materials and still give an acceptable quality.! . . . . The thing you and others should be aware of is that router based machines can never cut steel or aluminium like dedicated milling machines can.!!

Wish you luck and keep the designs coming.

BikerAfloat
01-08-2012, 09:13 PM
Hi Jazz,



I see some issues that will definitely affect it's ability to cut steel and will also affect performance in Aluminium.?

I am really not surprised by this :-) , it is why I have sought help on the design! I am starting to think that some of the videos of what to me at least look like flimsier machines cutting Ally accurately, might be using a bit of artistic licence!



The tall gantry won't be any where near strong enough.!! While it's sat directly on the bearings the what looks like 45x45 uprights just won't handle the forces steel and aluminium will put on it.

Although doubled up, the uprights are in fact just 40x20! so are as weak as soft smelly stuff in that case :-) I was thinking of joining the two Y Axis cross beams with a sheet of Ally to stiffen the entire structure, just haven't got round to adding it to the drawing.



The un-supported rails on the Z axis and to be honest the whole z axis design just won't be upto the job of steel or Ali.!

Don't know if your planning on putting any braces across the frame to support the bed.? But again to cut any hard material then extra support will be required.


To cover both of the above points, the Y Axis will travel over the cross members at the front of the X Axis and I was planning to work the material with the Z Axis as close to the top of its travel as possible. That means all loads will travel the miniumum distance to the strongest parts of the machine. Not sure if that will help enough? I am hoping to keep the centre as free from bracing as possible as I want to be able to engrave on Motorcycle engine cases, but I guess it is only a small amount more work to remove bracing to get big stuff up from underneath, when compared to removal of the Sacrificial bed and its support.



Please don't take my comments has pulling the machine down just comments based on quite extensive work building router based machines that can cut hard materials and still give an acceptable quality.! . . .


I didn't Jazz, it was what the drawings are posted for!



. The thing you and others should be aware of is that router based machines can never cut steel or aluminium like dedicated milling machines can.!!


I do appreciate that dedicated machines are the best way to go, they always are :-) and I would love to have space for more machines, but I will be working in a 6ft cubed area on my boat and I really only have space for this 1 machine outside the Pillar drill! Super accurate finishes are not going to be critical on the parts I make, they will be more art than engineering, so cutting speeds, hand de-burring and polishing, while a nuiscance aren't performance critical.



Wish you luck and keep the designs coming.

Thank you Jazz, I guess I'm always going to be in conflict with my ambitions for the way the machine HAS to be built and the way in which it will operate. As it stands the bearings take up a big chunk of the travel and I must admit I have run out of ideas how to reduce the gantry height or improve the Z Axis support without loosing even more travel or introducing the need for outside machine work! Any advice on how to achieve this and still maintain my production intent would be very gratefully received!

The only 3 rules here are:

1) I must be able to build it with just basic tools and a pillar drill.
2) There must be no physical outside help with the mechanical build - Virtual help with the design is OK!
3) As close to a 400x300 minimum working area as possible, within the above 2 constraints as possible.
3 and a bit) Sneaking in up to 100mm on X&Y is just about acceptable space wise, but I 'd rather avoid it!

That is the challenge I have set myself. Compromised performance will just have to be lived with, it is the nature of the beasty. Having said that the design can be changed to reduce the compromise!

Cheers,
Geoff.

John S
01-08-2012, 09:19 PM
Geoff,
Just a heads up but any extrusion ordered from KJN at Hinkley comes cut to length very accurately and requires no more work.

KJN Aluminium Profile (http://www.kjnltd.co.uk/)

Decent prices as well.

Robin Hewitt
01-08-2012, 09:58 PM
Jazz is the man, you won't go far wrong if you have faith and simply do everything he says.

Incidentally, putting 2 steppers on one axis usually ends in all sorts of problems.

BikerAfloat
01-08-2012, 10:30 PM
Jazz is the man, you won't go far wrong if you have faith and simply do everything he says.


I have followed Jazz's inputs on varied posts and have to say from what I have read I do have faith in his advice, however I was brought up to question everything where you have doubts, so I wont follow anyone blindly :-)



Incidentally, putting 2 steppers on one axis usually ends in all sorts of problems.

I have read that this idea can cause problems, yet one of my favourite machines out there is the Heiz from CNC-step, This was the inspiration for this feature being included in my build. They can't be that bad (well at least I hope they aren't) as their sales are in the 1000's now!

Advantages I see are:

1) Open bed design, this is important for me as I will want to get awkward shaped engine components in the machine for engraving.
2) More grunt for moving the heavy gantry.
3) Even loading of gantry to prevent, or at minimum reduce, racking.
4) Reduced component count
and 5) Possibly better accuracy when compared to a single central motor & belt system?

Disadvantages I see are:

1) Increased cost, but this should be a one-off.
2) Synchronisation/Alignment of the screws at the assembly stage, again this should be a one-off.
3) Machine ties itself in knots if one motor looses steps
or 3.5/4) Worst case scenario machine goes completely to peices should one motor stall or stop all together.

Prepared to accept any more Pro's and Con's before I freeze the design.

1 & 2 aren't my biggest worries, as a) this is an expensive tool anyway and I think (hope?) the advantages are worth it & b) this b@rst@rd is going to have so many adjustments required to get it straight and true, one more won't really matter :-)

3, 3.5 & 4) Scare the living daylights out of me!

Any advice to how best to go about reducing the risks and or providing the single motor & belt drive within my construction requirements would be gratefully received.

Cheers,

Geoff.

Jonathan
02-08-2012, 12:09 AM
however I was brought up to question everything where you have doubts, so I wont follow anyone blindly :-)

Excellent


I have read that this idea can cause problems, yet one of my favourite machines out there is the Heiz

Your options are limited to having two leadscrews on the X-axis - there is no way you'll get away without two when cutting metals unless the gantry is exceptionally strong which is almost never the case.

I use two motors on my X-axis and have not had any problems due to using two motors. When testing I have had one motor stall, but the gantry is sufficiently strong for this not to cause noticeable damage, especially since once one motor has stalled the other will invariably stall a fraction of a second later.
You can save a little money by only having one motor and using pulleys, but since you want the motor and driver later for a 4th axis you could always start with two motors and if you're not happy with it link the screws with a timing belt and use the now spare motor and driver on the 4th axis.

I urge you to reconsider not using ballscrews. I would add up the cost of the 4 leadscrews you are intending to get along with all the parts they require, then send Chai on eBay (http://www.ebay.co.uk/itm/3-SBR16-300-520-670mm-3-ballscrews-RM1605-3-BK-BF12-3-couplers-for-CNC-/251055862147?pt=UK_BOI_Metalworking_Milling_Weldin g_Metalworking_Supplies_ET&hash=item3a74187183#ht_1961wt_1166) a request for the price to get the 4 ballscrews (and rails) you would need with the standard end machining and bearing blocks. I'm sure you will be pleasantly surprised.

You mentioned using the 3Nm motors from CNC4You. These are a good choice since they will be more than adequate for this machine and offer the best price per Nm in Nema23/24 frame size. Currently you've got all the leadscrews direct drive which gains simplicity, however using timing belts gains a lot more than that. You can change the drive ratio (important to get a good feedrate if the leadscrew is quite a low pitch), motor alignment is no longer so critical, plenty of people seem to have problems with couplings breaking and belt drive provides damping which helps reduce resonance issues to name but a few...This (http://www.bearingstation.co.uk/Products/Pulleys/HTD_Pulleys/HTD_Pulley_5mm) is a good place to get the timing belts and pulleys.

Putting a sheet of aluminium on the back of the gantry will greatly increase it's stiffness since it will essentially eliminate bending of the gantry sides parallel to the Y-axis, thus reducing the tool deflection in the same axis.

JAZZCNC
02-08-2012, 01:06 AM
I have followed Jazz's inputs on varied posts and have to say from what I have read I do have faith in his advice, however I was brought up to question everything where you have doubts, so I wont follow anyone blindly :-)

Good upbringing because I wouldn't want anyone blindly following my advice and I only offer it to help the person come to the best design for there needs and hopefully steer them clear of any issues I know thru experience will come from what I see or comment on.!




I have read that this idea can cause problems, yet one of my favourite machines out there is the Heiz from CNC-step, This was the inspiration for this feature being included in my build. They can't be that bad (well at least I hope they aren't) as their sales are in the 1000's now!

Ermm I wouldn't be so sure and they are certainly massively over priced IMO.!


Advantages I see are:

1) Open bed design, this is important for me as I will want to get awkward shaped engine components in the machine for engraving.
2) More grunt for moving the heavy gantry.
3) Even loading of gantry to prevent, or at minimum reduce, racking.
4) Reduced component count
and 5) Possibly better accuracy when compared to a single central motor & belt system?

1) preference really but open bed is generally less accurate and more time consuming to set-up accurately.
2) Yes
3) yes
4) Erm not really when you take account of electrical side, wiring etc.
5) Absolutely NOT and the reality in use is that they can possibly be less accurate due to any missed steps in one or both motors slipping by un-noticed until the error shows it's self in the work, which is far too late for me.!!


Disadvantages I see are:

1) Increased cost, but this should be a one-off.
2) Synchronisation/Alignment of the screws at the assembly stage, again this should be a one-off.
3) Machine ties itself in knots if one motor looses steps
or 3.5/4) Worst case scenario machine goes completely to peices should one motor stall or stop all together.

1) The cost difference isn't so much after buying belts and pulleys.
2) Big disadvantage and you'll be doing it all the time (every time you use the machine if you want to be sure of accuracy) either by butting up to adjusted hard stops or using home switch's to sync.
3,3.5/4) Massive potential for serious damage when it happens and unless the slaved motors are run well within there limits then it will happen for sure and it will scare the living day lights out of you at best.!! . . . Best case it will tie it''s self in knots wasting a few hours setting and adjusting backup.!!. . . . Worst case with high probability if it happens at high feed rates damage will occur leaving you crying and shacking in the corner. .:thumbdown:

Slaved motors work fine if run within very safe tolerances regards tuning. They are very very intolerant of poor design causing any binding or miss alignment and will cause problems with stalling one of the motors while other continues on it's merry way causing chaos.!!

Belts completely remove this problem with very very good accuracy and are basicly fit and forget.!
In over 3yrs hard use my machine hasn't lost position regards screw sync more than few 10th mill and that was just in first few weeks due to pulley slippage and settling down.
In normal cutting use it has never missed a single step or lost positional accuracy. Again unless I cock up with programming and embed the cutter in something hard or try to run the gantry of the end it never stalls motor.!!. . . and if It does then no big deal just re-home the machine and I'm back on track with no damage to machine or hours straightening the machine out.!

The only down side to belts IMO is the look and the extra work designing into machine.? both more than worth the sacrifice or effort IME.

BikerAfloat
02-08-2012, 11:03 AM
Thank you both Jonathan & Jazz,

Subject: Twin Motors vs Single Motor & belts

Thank you both for helping me clarify this issue. In the light of your comments and a PM from AudioAndy who also recommended twin screws and belts. Since twin motors seem to be a riskier strategy than a single motor and belts. I'll play it safe, especially in the light of the following advantages of using the belts.

1) Flexibility of gearing,
2) Damping of drive
3) Removal of the weak spot of the couplings.
4) Fit and forget!
5) Simpler to sync leadscrews,
5) No risk of motors trying to tear machine apart - a big worry of mine!

One motor would allow me to mount the belt system at the back of the machine in what is effectively a "dead" space, I could then use the reduction of sticky out bits to gain a 100mm on X Axis travel - Win! Redesigning was inevitable so no worries there, measure twice cut once, as many a wise craftsman will advise!

One less motor & driver for the entire machine = effectively a cheaper 4th Axis when I get that far! :cool: Mmmm, fuzzy logic, but you catch my drift!

Q: This leads me to another question of course, is the 1x3.1Nm motor enough, or is it worth going to something more grunty?

Subject: Trapezoidal vs Ball screw.

While my Engineering head says Ballscrews have to be the best, my goal for this design was that involved a build where as much as possible the components would be compatable with the 20mm spacing of the slots on the extrusion, the aim being to design a machine to be built with a pillar drill and odd spaced holes always seem to fall on the edges of the sections and would be difficult to drill with said drill. I am fighting with what is best for me accuracy wise and what was intended as a design for other people with equally limited workshops... Okay writing this has allowed the grey cells to work in the background.

Since the support bearings for the ballscrews are more pricey than the solution I have drawn and at odds with the 20mm spacing intention, I'm thinking of a compromise. I am using 12mm ID Axial load bearings and a simple clamp system to fix them to the uprights.

Q: If I go with 12mm Ballscrews is there anything stopping me using this method of attachment? I gain significantly in accuracy and reduction in friction, while keeping cost as close to the Trapezoidal idea as I can AND still keep my 20mm spacing.
I will of course need to drop the ID at the motor end to allow the threading of the clamping nut, I need to do some more research now for the machining of the ends, I'm guessing it will be M10 and then hoping 10mm ID bearings are available!

Subject: Plating Gantry - No brainer :nevreness:

Onto Jazz's points...

Subject: Advice

My strategy for advice is now more concrete!

When it comes to advice. Evaluate it. Valididate it in the light of your own understanding. If the results prove to be incorrect, the responsibility is your own and not that of the advisor!

Subject: Heiz Machines

I have been re-evaluating these in the light of my readings here and yes for what you get they are expensive! Guess I was blinded a bit (lot?) as I thought I was getting one for 400 notes!

Subject: Pros & Cons

Advantages

1) Agreed, much more of a preference than an advantage, but as I really want to be able to engrave motorcycle casings it is going to have to be something I live with! I can minimise the compromise by measuring up the biggest clutch cover I can find and fixing permant braces in the bed upto that point, I can the add removable bracing to allow the access.
2) See question about motor above.
3) Twin leadscrews and belt drive it is!
4) Agreed, one less driver and wiring is a plus!
5) Ageed, two motors is too risky for me in the light of the above and errors in the work, screwing up a casing is a real worry and reduced risk is always worth it.

Disadvantages

1) I'm committed to belts and pulleys, the cost is now the cost :nevreness:
2) I can see that to be true, problem removed!
3-5) Problem and fear removed by belts!

As I mention above a redesign was inevitable and I can now see so many pluses for belt drives on all Axies (What is the plural of Axis? It's bugging the hell out of me!)

Yes belts aren't very pretty, but then it is a just a machine after all. It is more important the work comes out aesthetically pleasing and not the tool that made it!

Off to play about with design in the light of these changes, might even work a way of reducing the Gantry height an beef up the Z Axis, but since I was running low on ideas for this I will happyly take advice on these areas to!

Cheers both,

Geoff.

Robin Hewitt
02-08-2012, 11:50 AM
If you use 2 pulleys you need to check available belt lengths. If you use 3 pulleys to get belt adjustment, one of them will only use 1/4 of it's teeth, or less, so you will need bigger. HPC gears do a good selection of belts at reasonable prices (unlike their pulleys).

Make sure you get aluminium pulleys, the iron ones are cheaper but the weight will slow you down.

BikerAfloat
02-08-2012, 12:21 PM
Hi Robin

Thank you for your advice.


If you use 2 pulleys you need to check available belt lengths. If you use 3 pulleys to get belt adjustment, one of them will only use 1/4 of it's teeth, or less, so you will need bigger.


I'm going to start nosing around for belt drive applications, but if you could post drawing or pictures they would help me understand what you mean.



HPC gears do a good selection of belts at reasonable prices (unlike their pulleys).

Make sure you get aluminium pulleys, the iron ones are cheaper but the weight will slow you down.

I've a bookmark for HPC, but haven't reviewed what the sell yet, will go and have a nose soon.

With regard to the weight, is it really that bad when compared to the weight of the gantry? I know rotational inertia is a problem for acceleration where large diameters and masses are involved, lighter flywheels on cars & bikes don't improve power, they effectively loose mass that needs accelerating, but then we are talking several lbs saved at 10s of inches diameter there, rather than ounces at a couple of inches. I think cost will be more of my consideration here rather than acceleration, though significant, real world improvements can always change my mind where cost is involved!

Cheers,
Geoff.

Robin Hewitt
02-08-2012, 01:51 PM
I forgot to explain :beer:

A heavy pulley is a flywheel, flywheels have long been used to add inertia to systems, and if you look at the maths you will find they do it well. It takes surprisingly little effort to accelerate a gantry, if it weighs 20 lbs then a 20 pound force will accelerate it at 1G, same as if you dropped it. If you add unnecesary inertia to the system you have to watch out for that moment when you hurl the gantry in to reverse. That is the moment you risk losing steps and blowing your position. Unnecessary inertia is to be avoided for that reason.

As you like explanations I should also warn you about choosing stepper motors by holding torque alone. For some obscure reason the hobby market has settled on stepper motors with an arbitrary 200 full steps per rev, so the field coils have to turn the rotor 1.8 degrees. If you use a large rotor you get more leverage on the shaft but the pull in distance for 1.8 degrees is larger than for a small motor. Unfortunately as the distance increases the magnetic field falls away by the inverse square law so you tend to lose more than you gain.

Next problem is that the suppliers have found that nobody seems to care a fig for the actual motor performance, they only look at the holding/detente torque for the motor. Obviously the holding torque is measured with the minimum gap so big numbers are easy achieve so that is exactly what they do. What you are really interested in is the pull in torque and the inductance of the field coils.

You can "fix" a large 200 step motor by increasing the volts but that is expensive in the driver/PSU department. When choosing a motor you want to view holding torque as a simple indicator so you gett in the right ball park, what you really want is a graph of torque against speed and see how it goes with what you are trying to achive in accuracy while still giving a good rapid which gets more important as the size of the machine bed increases.

Edit: There is also a tendency to sell motors in sets of 3 for XYZ, why anyone would want to use the same motor for 3 completely different tasks eludes me.

irving2008
02-08-2012, 03:48 PM
Geoff,

You might find this useful: http://www.mycncuk.com/forums/faqs-problems-solutions/1524-what-size-stepper-motor-do-i-need.html

As Robin has already alluded, stepper motor holding torque is what it takes to move the rotor from a stationary position. Once it's moving the torque available is considerably lower and essentially flat until you get to what is called the corner speed after which it becomes inversely proportional to speed. Ideally you run your motors at or just below this corner speed. The corner speed itself is dependent on the rise time of the current in the coils, and that depends essentially on the ratio of the coil inductance to its resistance. As Robin said, one way to improve the corner speed is to drive the coils harder by applying a much higher voltage (most stepper coils are rated for 3 - 5v but will often be driven from 12 - 80v) and controlling the current to avoid burning them out - constant current drive (expensive, heat producing) or chopper regulation (cheaper, but noisy and prone to other side effects).

Sadly, very few stepper manufacturers provide graphs of torque vs speed at the rated current so its always a little bit of 'what has everyone else done'.

BikerAfloat
02-08-2012, 03:54 PM
Thanks for your reply Robin,

I forgot to explain :beer:

A heavy pulley is a flywheel, ...

... Unnecessary inertia is to be avoided for that reason.


Should have thought a bit more about my reply, I was finishing it before having to go out!

I was heading down the right track, I just didn't get to the end in time!

I have a real love for the old Mini and the A-Series engine (Yes this is still on track) sadly can no longer justify the expense of owning one along side my pickup truck :-( In the tuning manuals I had there was the formula that proved a few pounds off the weight of the flywheel equated to a significantly larger weight reduction in the vehicle. Obviously this effective weight loss was reduced with each gear, as the rate of acceleration decreased. Had I given myself a bit more time to think, it would have been clear to me that this holds true with the mass of the pulleys vs the mass of the gantry Doh!!!!


As you like explanations I should also warn you about choosing stepper motors by holding torque alone...

...Edit: There is also a tendency to sell motors in sets of 3 for XYZ, why anyone would want to use the same motor for 3 completely different tasks eludes me.

Oh yes, another can of CNC worms! I have done a bit of reading about this and was aware of the difference between holding torque performance and dynamic performance.

There are so many variables in each component, there comes a time when you have to say enough - any more information your brain will fry - and base your choices on what seems to be the best given what you know and what the rest of the world is doing in a similar situation.

I agree with your final statement, I had already thought that in an ideal world the motors need to be sized lower performance for Z, rising through Y to X as each axis in that order, has relatively more to do. However since this is not a racing machine where everything has to be maximum performance and minimum safe construction, I couldn't see the harm if Z&Y were a little over specified, when compared to X. As you will have seen, I have asked above if a single 3.1 Nm is enough for my X Axis.

As you can imagine I have done lots and lots of reading and seen large machines working with quite small motors where budgets are tight and small machines apparently grossly over powered when it has been clear money was little object!

My choice of motors was down to several parameters:

1) Most machines I have found in the size range I am after (and some at 8'x4') use Nema 23s, so this seemed to be a the most sensible choice for frame size. Incidentally it also fits in nicely with my choice of extrusions.

2) This page (Drives and Steppers~Solsylva CNC Plans (http://solsylva.com/cnc/drives_steppers.shtml)) had the following statement: "Steppers in the ~300 oz.in. range can push a full sized router, but they lack the power to push the router to its limit. The steppers will most certainly stall before the router does." That ruled out the lower torque range of the Nema 23s. Also I have a copy of the TAB CNC Robotics book by Geoff Williams, his steel construction machine gets away with motors that are at best 220oz.in. So I decided on 300oz.in minimum.

Since this project does not have an unlimited budget, the best "Bang per Buck" method was going to have to be used. Also I chose to make the assumption that for a given frame size and therefore presumably similar construction a Higher holding torque should lead to a correspondingly higher dynamic torque.

My search led me to the 439oz.in (3.1Nm) motors from CNC4You at around 100 for four. At roughly 30% over the torque suggested by what I could find at the time, I guessed these would probably be man enough. My limited knowledge and obviously finite research makes these the best cost/performance ratio I can find. Given my resignation to the fact that finite budget machines are always a compromise, I am happy with my choice, but I am willing to be proved wrong!

Q: Does anyone know of 4 better motors out there for the same money, give or take a Tenner?

Now I'm going to be using belts to drive the twin screws the 4th motor is going to rest in a draw until I get round to my 4th Axis.

Cheers,
Geoff.

BikerAfloat
02-08-2012, 04:14 PM
Hi Irving,

Thanks for the link, I'll check that out when my brain cools down!

Cheers,
Geoff.

Robin Hewitt
02-08-2012, 04:50 PM
No need to break your brain if you use sensible units such as the British standard fat bloke

The standard fat bloke weighs 16 stone which translates conveniently to a downward force of 1000 Newtons.

Direct drive on to a 5mm pitch screw requires 0.8 Nm of torque to lift one fat bloke off the floor.

Look at your cutter in it's collet and ask yourself, how many fat blokes could stand on the sharp end of this before it snaps?

Multiply by 0.8, call it Newton meters and anything above that is superfluous.

Jonathan
02-08-2012, 07:22 PM
I'd be more worried about accelerating the fat bloke, although it's still not going to change Robin's conclusion that a smaller motor is fine for your Z-axis.

The question really is do you envisage using the motors on a larger/heavier CNC Router, or a milling machine in the future? If so then it's sensible to get the 3Nm motors as they a very likely to be well matched to the future machine. If not then there are motors with a lower rated torque, but would perform better on your machine due to their lower inductance enabling them to reach a higher speed than the 3Nm motors. For instance play around with Irving's spreadsheet to compare this 1.85Nm 1.6mH one (http://www.zappautomation.co.uk/sy57sth763008b-nema-stepper-motor-p-38.html?cPath=9_159_42) to the 3Nm motor for your size machine. The annoying thing then is you're spending more money on a smaller motor, so if they do turn out to be better in theory you've got to be sure you wont regret not having the bigger motors in the future for something else. Additionally the 3Nm motors are fit for purpose, so if they're cheaper than the better alternative then why not?

One point about the X-axis slaving - I wouldn't compare two motors and no belts to one motor and belts, since the belts have so many advantages anyway that you should use them with either system. Given that, out of your list of reasons, the only one that applies is you pretty much eliminate the chance of racking the gantry if the screws are linked. What are the chances of one motor stalling if you have two? Jazz said he's never had his stall since setting up with one motor and I've not had problems with two motors after tuning.

With both the motor selection and drive mechanism, in the end either system is fit for purpose so there's no point in me suggesting that you should use one or the other. What is worth suggesting though is if you do stick with trapezoidal screws, then consider substituting the nuts for the 'wonky bearing drive nut' method I started out using:

648764886489



http://www.youtube.com/watch?v=m6k8Jz_-WCk&feature=plcp

Very low backlash, low friction and I bet you could make it with hand tools. There's certainly room for improvement on my design, some of which is discussed in my build log.

Hopefully I'm wrong, but it seems from your previous posts that you're considering not machining at least one end of the leadscrews presumably to save cost? If so forget it since the accuracy will be so poor.

BikerAfloat
02-08-2012, 07:36 PM
Robin,

That is excellent, when I stop laughing and the tears have cleared, I'll see if I can find how many fat blokes can stand on the average cutter, should be an interesting Google!

Now looking at Irving's stepper motor tutorial, will then see if I can estimate the mass of my machine components and see where I go from there. Since I'm quite a bit heavier than a BS Fatbloke I keep thinking I could snap (or at least bend) most things that will fit in a Kress collet!

Do we have shear force tables for typical cutters anywhere? Is it a common figure maufacturers supply? or do we just go by Dia of the cutter and its material spec?

I'm guessing snapping during plunging is much less of an issue as the material is in compression. So am I right in thinking that as long as the shear force for a cutter is not exceeded things should be OK?

Cheers,
Geoff.

Jonathan
02-08-2012, 07:47 PM
Do we have shear force tables for typical cutters anywhere? Is it a common figure maufacturers supply? or do we just go by Dia of the cutter and its material spec?

Unfortunately it's not trivial to get an accurate idea of the forces on a milling cutter since there are so many variables, some of which are hard to quantify. But if you say 20N for cutting aluminium and 50N for steel with your average size cutter (very vague statement there on purpose) you wont be far off...


I'm guessing snapping during plunging is much less of an issue as the material is in compression. So am I right in thinking that as long as the shear force for a cutter is not exceeded things should be OK?

Quite the opposite actually as the geometry of the cutter is not favourable. Plunging with a milling cutter puts a very high axial force on the spindle, so it's generally something to be avoided by instead moving the cutter in Z and X or Y at the same time to enter the material - i.e. ramping.

JAZZCNC
02-08-2012, 08:11 PM
Ok lets bring this back to real world use and implementation.?

While the motor calcs like Irvings are great they are really only good for giving a ballpark figure IMO.!
Unless every aspect of the machines friction and resistance to movement etc are known, which can vary wildly dependent on design, build quality and component quality then it's very difficult to accurately choose the perfect and ideal motor.
Also like Irving pointed out it's very difficult to get real useful motor torque curves graphs from manufactures.? When dealing with cheap motors this is no accident either because they would show that they are really quite below what people might expect.? Only the better motor manufacturers tend to give them and these cost far more money than the average DIY user would want to spend.!

In real DIY built in the shed, garage, basement or coal house and soon to be back of a boat.!! . . things don't often work out like the Calcs or graphs would have you believe so some (plenty) sticky wiggle room needs to be factored in.
Then there's electronics side and in-balance that using different sized motors brings to the control box and it's power requirements.?
Lets take this machine or system for instance.!
If ball-screws are used then it may be possible to use 1.85Nm motors which will run on 40-45V using 50V drives for 2 axis but the 3rd twin screw setup will need at least larger 3Nm motors and 65-70V and 75V drives. This means 2 different PSU's costing extra money and space.
The only advantages to the smaller motors will be they spin slightly faster which really in all probability won't be required, they will accelerate slightly faster but again the little extra will be negligible in real use for this machine, the total cost will be slightly less.
The while on paper the larger motors will accelerate slower and spin slower in real world use the difference won't make much if any difference to this machine other than cost. This is offset by the extra PSU required and not so massive.
The larger motors on the other hand will give great over build "wiggle room" while not having any real detrimental affects to machine performance.
Yes While it's very true Bigger is not always better in this case the difference won't be so much it affects performance to be worth bothering about.!

Then there's the longevity factor.? An over spec'd machine tends not to be so stressed and can run well within it's limits giving long life to both motors and drives.

That's my view on the motor choice obviously others have there's.!


Regards the twin screw and 3.1Nm then yes if you use ballscrews with 10mm pitch and gear either 2:1 or 1.5:1. This will increase torque and resolution while still keeping the motors in a nice RPM range well below the corner speed while cutting. The sacrifice will be rapid speed which to quote John S only any good for "dick slapping".

Like Jonathan I urge you to use ballscrews and the difference in cost if bought from china won't be very much and really lead screws can't be compared with even cheap ballscrews unless high quality lead screws which cost more than ballscrews.!

Use 16mm as well not 12mm.

Also if you use the 90x45 profile from KJN then the BK/BF blocks fit the slots and can be bolted straight on. Also the BK/BF blocks from china are ridiculously cheap and I see no point in making your own.?

Robin Hewitt
02-08-2012, 08:23 PM
Tools don't snap when you plunge, everything will want to vibrate when you plunge but not break. They usually break when your aluminium starts extruding, when you accidentally G zero in to the side of the billet and for no reason at all whenever it is most inconvenient. You might expect them to go flying off like rifle bullets heading straight for your eyeballs, but they actually just drop right where they are. It's weird.

Cutting forces are probably greatest when slotting. If you have enough power to snap the tool you cannot use any more.

Of course you hardly need any power at all for rapd transits because there is no cutting force required. You adjust the accelerations/decellerations to allow for the gantry inertia.

Jonathan
02-08-2012, 08:23 PM
The sacrifice will be rapid speed which to quote John S only any good for "dick slapping".

That and bed surfacing. It's much more useful to have high acceleration, since this dictates how fast the machine can go round corners which is important for toolpaths with fine detail.



Like Jonathan I urge you to use ballscrews and the difference in cost if bought from china won't be very much and really lead screws can't be compared with even cheap ballscrews unless high quality lead screws which cost more than ballscrews.!

Use 16mm as well not 12mm.

Yes and yes...


though I have seen 8'x4' machines with 12mm

Seeing them doesn't mean they're any good! Unless you need a rotating nut on a 16mm screw (which is pushing it for 8') you'll need at least 20-25mm ballscrews on an 8' axis to get sufficiently high critical speed.


Also the BK/BF blocks from china are ridiculously cheap and I see no point in making your own.?

I make them myself since then I know the quality of the block and bearings is good and I don't want to limit my design by having to fit standard size blocks in. But for your average machine and particularly without the tools to make them yourself the blocks from China are excellent value.

BikerAfloat
03-08-2012, 01:26 AM
Ok lets get this out of the way

Information Overload

Ok this is really hard for me to write, I have to say what I have to say or I will have to stop posting. Without going into too many details, it has taken me a tremendous effort to post what I have posted so far. Lets just say, that if things had gone differently on the 2 days leading upto my first post, I may not have made my introduction ever, let alone any subsequent posts.

When I say I am struggling with overload, I really am, with every new bit of information I find it harder to see a way forward with this project. I never used to be like this, having a label and a knowledge that it is a bit of chemical imbalance does help, but I don't really understand how or why it fecks me up this way, So I don't expect you guys to.

I don't want to sound ungrateful or ignorant and all previous advice is stored for when I am better able to deal with it.

So how do I move forward?

I really need some structure to this, so I think what I will do, is start at the cutter tip or rather the router itself and work backwards as that is the way I have worked when designing the first draft of the machine, not sure if this is odd, but hey ho! I will explain my reasoning as to how each decision was made.

Given I want to build a machine witin the pillar drill only build parameters, how can you help?

Well for a start, please bear with me and let me go through this bit by bit. If I set the pace I'll get there in the end.

If at any point my reasoning is dangerous, completely flawed or the machine cannot work because of it, please tell me! I will then ask for more help to fix that area.

I have tried to find the best prices in the UK and EU primarily for the bits to build this, nothing against the ROTW, just a preference for supporting the local guy. After much hard thought I am going to go for Ballscrews will have to redesign accordingly. Since you all seem to buy from Chai (?) and all seem happy with him, it makes sense for me to do the same. Any help in beating the prices I've found would be gratefully received. Second hand is not at ruled out, neither is eBay if I can beat you lot to the bargins :-) Free, while being awesome is not what I am expecting here. I want to pay my way properly or be able to at least help someone, somewhere in exchange for goods if they are FOC, even if it is not the supplier directly and I will of course want to pay P&P. Not Karma exactly, but I'm not after a free ride either.

In an ideal world I'd have all the cash together before I start the build, but unless I am very lucky this won't happen. This is a very vague hope, but I guess I am looking for a strategy to make this peicemeal gathering of the stuff at least bearable.

Since there are flimsier (flimsyer ? No that looks worse!) machines out there and no one has shouted "No! don't do it, it is a complete disaster" I guess I am at least the right ballpark for a working machine.

Ok to support my choice and ambitions, Amongs the dozens of videos of machines in action, this video of a Heiz S series machine Milling In Steel (http://www.cnc-step.de/frasanwendungen-der-high-z-cnc-frase/2d-frasen-von-harten-metallen-wie-messing-und-stahl.html) caught my attention. These machines are neither the gruntiest or the sturdiest out there, but here is one cutting steel at what to me is a totally acceptable pace - I couldn't do it with a fret saw or jig saw at that speed or accuracy, so I would be very very happy with this as an absolute peak of my ambitions for this machine. It hasn't got to do it all day, every day. Just be able to do it occaisionally. The speed accuracy and finish are not critical on any material, I want to be making more artistic stuff than I do engineering components and a bit of hand finishing is a lot better than a lot of hand cutting.

I started with a combination of the Heiz & Marchant Dice type constructions running through my head and I hope I have come up with a machine that is stronger than either. I also hope to be able to get it completely built with enough software to make useful stuff for around 1500.

I'd now like to see how close I can get to these goals with my comstruction restrictions and you step by step guidance.

Item 1 - Spindle Choice:

Worst case: Use the router I already have - this is not much more than a single speed noisey toy - Ruled out as non-starter!

The ideal: A water-cooled, fully speed controlled auto-tool-changing spindle! - Ruled out as I had to stop somewhere!

My Choice:

Model: Kress FME1050-1 High speed spindle
Volts: 240V with IEC connector
Spindle speed: 5000 to 25000 rpm
Power: 1050 Watts

Reasons for choice:

1) These seem to be the aircooled router of choice, CNC-STEP, Marchant Dice and
countless home builds use them.
2) It's the gruntiest one they do. At least as far as I know.
& 3) I liked the wide speed range it offered, since I will be machining mostly wood
and I want to have a go at machining Brass, Aluminium and sheet Steel, its relatively
low speed capability appealed to me as it must be a help when it comes to metal
cutting.

Chosen Supplier:

Model Engineer's Digital Workshop
Price: 168 inc VAT - This was the best price I could find

One question: Is this the best value for money I can get for an air-cooled router?

Sorry for the length of posts, it is just where I am atm.

Cheers
Geoff.

Jonathan
03-08-2012, 02:26 PM
I cannot reccomend using a Kress router for cutting metals - in the end it's still a router not a spindle. Whilst clearly from the video you linked to it is possible to cut metals with it, that's not really saying much on it's own. You could cut what they did in the video with a hand file, but that doesn't mean it's a sensible method. One thing you don't get from videos is the impact on the life of the tool, which is important here since that is putting a high force onto the Kress' relatively small bearings, which will have a detrimental effect on their life. One often sees videos where people are pushing the machine or tool too far, maybe it works, but if the video lasts 2 minutes and the tool only lasts 5 minutes at that speed then the video is misleading.

Much better would be to get one of the water cooled 2.2kW spindles from China that you've no doubt seen in other build logs. Among other things they have much higher rigidity and lower runout than any router, including the Kress. For cutting steel you need quite high torque at a low rpm, which is something most high speed spindles and routers lack, but to an extent you can get away with it by using small carbide tooling ideally with the right coating.

The obvious problem is you're in a similar situation to me when I starting building the router - it needed to be cheap as otherwise I couldn't make it. For that reason alone I started off by using a router for about 6 from the local car boot sale. It was fine for cutting wood at a modest speed, but no chance of cutting metal properly. After (approximately) a few months I did break it by being a bit too ambitious with the tool length, but by then I'd done enough with it to persuade the 'Bank of Mum' that it was worth getting a better spindle, so after a similar discussion on the forum I got the 2.2kW water cooled spindle. The difference in performance is huge.

So basically I think you should try a very cheap router to start with as that'll be fine for making signs and other bits of pieces from wood, then you can re-invest the profits in getting a proper spindle and start cutting metals. Unlike the rest of the machine you don't loose much money by going for the very cheap option to start with and still have a useable machine.

deannos
03-08-2012, 03:31 PM
So basically I think you should try a very cheap router to start with as that'll be fine for making signs and other bits of pieces from wood, then you can re-invest the profits in getting a proper spindle and start cutting metals. Unlike the rest of the machine you don't loose much money by going for the very cheap option to start with and still have a useable machine.

I totally agree with this. I started off with the MDF, threaded rod and skate bearings contraption. Every body on here told me it was a big mistake and it was in the end. It worked ok, if you could call it working, but only lasted a couple of months. It was nice to cut some things and i did have a big smile when it first came to life. But i got frustrated with it limitations after a week or so. It all warped due to moisture etc, mdf sucks it up like a sponge. I'm now hopefully going to build a totally new machine using ballscrews, supported rails etc. The only thing i will reuse is the motors, electronics and the router. But the router will be changed for a spindle in the end. I probably lost around 100, which would have been better spent doing it right the first time. I'm still struggling with the design, nearly 8 months on that, but every one on here gives constructive criticism, i mean help:adoration:. I believe you have a big advantage in that you can use cad to design etc. so listen to the guys on here and it will be right and right the first time.

JAZZCNC
03-08-2012, 04:39 PM
I completely agree with Jonathan regards the spindle VS router but would also like to point out one other advantage the WC spindles have over router based machines and IMO it's significant esp for some work like V Carving and 3D work.? . . . DUTY CYCLE.
The cheap BQ 30-40 jobs have a duty cycle about the same has chocolate in sun shine.!! The better Kress routers claim about 8hrs Thou I very much doubt they will do too it many times before showing the affects.?
When cutting decorative type work, esp things like litho-pains and 3D carvings then the cutting times can easily run into 12+hours and far longer if large sizes.
The WC spindles can run 12hrs without batting an eye lid and it's not unusual for me to leave mine running none stop for 20+hrs.!!

I know we all want to keep costs down but some times your far better off waiting an extra few weeks or months to find the extra money. When the difference gets close like with the Kress VS WC spindles then it really does become worth the wait has they don't compare to each other. Like Dean says your CNC experience will be so much more pleasant and rewarding not to mention in the long run far cheaper.!!

BikerAfloat
03-08-2012, 10:08 PM
Thank you Jonathan, Deanos & Jazz,

I agree totally, however I cannot use "best practice" for this machine, every upgraded component drives the cost up and makes this machine more and more unlikely to happen!

Sorry for yet another long (and in the end somewhat contradictory) post!

I had hoped that between my introduction and the "Information Overload" post I had made my situation clear, I think I have missed something, I'll have another go.

I'll relate my CNC desires to cars and motorcycles to give you an idea of my needs...



Scale

Cars

Motorcycles

CNC



Dream

Lotus Elise

Full hand built custom

Servo Motors, Water-cooling
No compromise frame 8x4 cutting area



Best I've ever managed

Second hand Alfa Romeo 1600 Twin Spark

Moto Guzzi 1100i Jackal

This construction of machine with Water-cooling and ballscrews.



Reality Now!

Skoda Fun Pickup
"Jack of all Trades"

Had to sell it, but last bike XJ650 Yamaha - "Jack of all Trades"

This build
"Jack of all Trades"



Unacceptable

Beat up Opel Corsa

Beat up old CB500 Honda twin

"All tread", gas pipe, skate bearing
lash-up




This table shows a "Law of Diminishing returns"

At the bottom, things are cheap but barely functional and you'd soon be cursing them.

At the top, and certainly on paper they are better than everything else, but their price and true performance envelopes are beyond me and most likely always will be!

My aspirations are for the 2nd level, a bit better than I really need, but with a bit of a spare capacity for pushing MY limits, but not so much they are too scary for mundane tasks.

Where I am, the top of the performance envelope is still really enough for my needs, but I appreciate the margin for error is much reduced. However I accept this, as in everyday use, the "Jack of all Trades" does most of what I ever really need.

The aim is for the machine to be more capable than the entry level machines (such as say the Heiz S400) and around 500* less in total build cost. As I tried to say in the "Information Overload" post:

I need to know that this design will not self destruct and I have found the best value for money for a given component. Or for a given budget (assume I am really maxXxed out with the prices I will give) is there something better?

*I have a final figure if 1500 in mind, this is already 50% more than I can really justify at the moment, I have seen the "think of a figure and double it" in many more places than this. However, I have priced everything I have added to the drawing and virtually all the control components and still have a bit of space to breathe in this figure.

I have 410 to spend at the moment, my goal is to come out of this discussion with a set of plans for a scaleable machine that will most importantly, work and that I could sell to help fund the rest of the build. That will be hard I know, but it is not impossible. There have been plenty of "crowd funded" CNC machines in the USA, so why not one in the UK? I also plan to offer upgrade drawings using the machine to make its own upgraded components - see later posts!

Most of the plans I have found are for MDF and other wooden structures. I have found only one set of plans for an extrusion based machine, so I hope there will be space for me to sell some of mine, I can't be the only one thinking MDF is not really the material for a such a machine!

I am taking responsibilty for the path I am taking, I know you want to help me by suggesting that I spend just a bit more money you won't regret it, I can see that totally and it is excellent advice, but I am spending 50% more than I can really justify and planning on spending over 200% more than I actually have already!!!

So at the risk of upsetting you all, please just help me by answering the direct questions I ask and keep the "If onlys" for another day, when I am more able to keep up with them and do something about them. :nevreness:

OK one last Kress vs Watercooled, the following is based on my findings for the WC spindle, I'll be asking questions at the end, so please pay attention as many a teacher has said! :nevreness:




Kress

Watercooled & VFD



Min Speed rpm

5000

8000





Just under 170

Best I found 250



Additional cost excluding cutters and collets

0

Pump, tubes and a bucket! Say 20




Ok so 100 isn't a lot, but it is 4 stepper motors! Which may be enough to save this project.

Mmm why does the brain work and find solutions from advice while writing posts? Not going to re-write so please prepare to laugh while I shoot my self in the foot!

OK, my strategy is going to be as follows:

1) Original aim was to use Kress, many people including me are happy with these, so I will keep that possibility in the plans. A wider router clamp for the WS Spindle still allows for this so Win/Win!

2) Get drawings for WC Spindle as at 80mm I will need to draw a new Z axis to make space anyway. Downside is a few more millimeters will have to be pinched from an already less than ideal final travel on X&Y (Although I can scale each axis up, I have space constraints to work in).

3) See if I can find my old hand-held router and measure it up, from memory it may be bigger than the WC spindle, so to use it I will need the redraw anyway!
4) Whatever happens, use said router in the CNC machine to start making stuff, 170 less to find to get going and aim for WC Spindle, if it breaks before I'll try and have to find the rest!

Questions needing answers:

1) Does anyone know of a better price for the Kress than I posted earlier?
2) For the price of the Kress, can anything beat it?
3) Bearing in mind and forgive me if I am wrong, a reason given against the Kress and in favour of the Spindle was on the grounds of speed (See table above as to why I am asking this question) How do you bring the WS Spindle speed below 8000rpm?
4) What equipment is involved in the solution to 3?
5) Where is the best place to buy solution 4) and the WC Spindle?
6) Does anyone have the Drawings for the WC Spindle in 5)?
7) Can you advise how best to mount the Spindle in 6)?

I think that is all I need to ask for the router....

& finally 8) I'd love to see more extrusion based plans, in order to evaluate them for later what have you guys found?

Cheers
Geoff.

wilfy
03-08-2012, 10:15 PM
just something to consider on your router vs spindle cost, i'm pretty sure i saw someone recently buy the cheap chinese spindle that johnathan and jazz talk about for the same price your looking to pay for your router.. if i can remember where i saw the post i'll come back and link it for you

wilfy
03-08-2012, 10:25 PM
WATER-COOLED MOTOR SPINDLE 1.5KW + MATCHING INVERTER f4 | eBay (http://www.ebay.co.uk/itm/WATER-COOLED-MOTOR-SPINDLE-1-5KW-MATCHING-INVERTER-f4-/170593448159?pt=UK_BOI_Industrial_Automation_Contr ol_ET&hash=item27b82970df#ht_11524wt_1396)

here we go.. i dont know enough about spindles yet to know if it's a good one or not, but my point is there seems to be a fair bit of choice around your price point for a longer lasting W/C spindle

Jonathan
03-08-2012, 10:45 PM
Why exclude collets in the comparison? The price of the Kress collets is huge compared to the ER20 collets for the spindle if bought in China. Clearly it depends how many different size tools you end up using, but if it's a fair few the price difference wont be so great...


I don't see the point of 1) and 2) since if you use a very cheap router to start with (suggest going to car boot if there's one near you and getting a variable speed one) you wont need to buy a Kress.


3) I've used the WC spindle at 5000rpm to drill aluminium with a 4mm drill, so although the torque is limited at that speed there's still enough to be useful.
4) It's just a matter of tweaking the settings on the VFD and having good cooling. Although it helps to buy a better (more expensive) VFD.
5) eBay
6) Yes.
7) Here's one or two I made earlier:
65026503650465056506
I'd advise using 1/2" thick aluminium.


WATER-COOLED MOTOR SPINDLE 1.5KW + MATCHING INVERTER f4 | eBay (http://www.ebay.co.uk/itm/WATER-COOLED-MOTOR-SPINDLE-1-5KW-MATCHING-INVERTER-f4-/170593448159?pt=UK_BOI_Industrial_Automation_Contr ol_ET&hash=item27b82970df#ht_11524wt_1396)

here we go.. i dont know enough about spindles yet to know if it's a good one or not,

Problem with that one is it only takes ER11 collets, so you're limited to up to 7mm cutters. That's one excellent reason to get the 2.2kW spindle - it uses ER20 collets which accept up to 13mm tools. Bear in mind several sellers here have used 'best offer' with these spindles to get them cheaper.

BikerAfloat
03-08-2012, 11:04 PM
Cheers Wilfy,

Saved in watch list for future reference!

wilfy
03-08-2012, 11:38 PM
Why exclude collets in the comparison? The price of the Kress collets is huge compared to the ER20 collets for the spindle if bought in China. Clearly it depends how many different size tools you end up using, but if it's a fair few the price difference wont be so great...


I don't see the point of 1) and 2) since if you use a very cheap router to start with (suggest going to car boot if there's one near you and getting a variable speed one) you wont need to buy a Kress.


3) I've used the WC spindle at 5000rpm to drill aluminium with a 4mm drill, so although the torque is limited at that speed there's still enough to be useful.
4) It's just a matter of tweaking the settings on the VFD and having good cooling. Although it helps to buy a better (more expensive) VFD.
5) eBay
6) Yes.
7) Here's one or two I made earlier:
65026503650465056506
I'd advise using 1/2" thick aluminium.



Problem with that one is it only takes ER11 collets, so you're limited to up to 7mm cutters. That's one excellent reason to get the 2.2kW spindle - it uses ER20 collets which accept up to 13mm tools. Bear in mind several sellers here have used 'best offer' with these spindles to get them cheaper.

i said i dont know if it's good or not as i dont have a clue and i'm glad someone stepped in to correct me, however if we are talking about longevity, yes that one might be limited in collet size, but if this is the absolute max price he can go to.. then the question is does he buy a router that will burn it's self out with a few hours hard use with the right size bits, or buy a spindle that will keep going even if it means he has to make more passes due to limited bit's he can use?

BikerAfloat
03-08-2012, 11:39 PM
Why exclude collets in the comparison?


Ignorance/Stupidity you choose! Made the assumption that I wouldn't buying enough collets to bring down the price difference significantly.



I don't see the point of 1) and 2) since if you use a very cheap router to start with (suggest going to car boot if there's one near you and getting a variable speed one) you wont need to buy a Kress.


I did say I'd shot my self in the foot! Even in the light of my foot shooting proposed strategy I would like to know the answers just out of curiosity.



3) I've used the WC spindle at 5000rpm to drill aluminium with a 4mm drill, so although the torque is limited at that speed there's still enough to be useful.

4) It's just a matter of tweaking the settings on the VFD and having good cooling. Although it helps to buy a better (more expensive) VFD.


3) Ok the spindle I found stated 8000rpm minimum, I guess from this there are VFDs that do 5000?

4) More money = better, that figures



5) eBay

6) Yes.


5) As expected, is there a preferred sell like there is with Ballscrews?
6) LOL! Would you be so kind as to post them for me or PM them to me?



7) Here's one or two I made earlier:

I'd advise using 1/2" thick aluminium.


Nice work! Several leagues ahead of what my 43mm Hole drill and extrusion clamps will be! Once I know I can work my machine with the router, I'll make it machine its own replacement a new home!



Problem with that one is it only takes ER11 collets, so you're limited to up to 7mm cutters. That's one excellent reason to get the 2.2kW spindle - it uses ER20 collets which accept up to 13mm tools. Bear in mind several sellers here have used 'best offer' with these spindles to get them cheaper.

Thanks for the collet info, I have stored away for a later date.

wilfy
03-08-2012, 11:45 PM
right i've just remembered a thread on another forum i was pointed to.. this guy started off how you plan with just a plain simple router.... i'll not spoil the outcome for you, but have a skim through this
Modding Project: DIY CNC - V3 Reinforced Z Axis - Page 3 - bit-tech.net Forums (http://forums.bit-tech.net/showthread.php?t=179960&page=3)

wilfy
03-08-2012, 11:51 PM
it gets interesting around page 8

BikerAfloat
04-08-2012, 12:12 AM
...but if this is the absolute max price he can go to.. then the question is does he buy a router that will burn it's self out with a few hours hard use ... or buy a spindle that will keep going ...

Excellent Wilfy, you have totally understood where I am going with my questions!

wilfy
04-08-2012, 12:37 AM
Excellent Wilfy, you have totally understood where I am going with my questions!

i understand as i am at pretty much the same price point as you for my table and have the same desire to keep costs down.... the reality is that water cooled is better than the kress, defining how bad a 1.5kw spindle is compared to the other options seems to be the hardest thing to get out of anyone. as i said before if the w/c spindle has to do twice the work a kress could do but the spindle for the same price lasts more than twice the time the kress does... than it already pays for itself... if it lasts 4x or more then even if the trade off is it takes longer to make everything the fact your not buying new parts every couple of hours work makes it priceless...

if however someone turns round and says if you dont have a 2.2kw W/c spindle you wont be able to cut this that and the other then i would have to take some consideration in to the chances of me wanting to cut them things.

Jonathan
04-08-2012, 12:40 AM
Excellent Wilfy, you have totally understood where I am going with my questions!

I think everyone participating in this thread understands where you are coming from since you have already made it perfectly clear. Jazz and I are just attempting to make sure you know the advantages and disadvantages of every option.

The absolute maximum price you can go to is already less than the cost of the 1.5kW ER11 spindle, hence you're going to have to wait to get a spindle anyway so all it would gain is getting the better spindle slightly sooner then some time in the future regretting not being able to use any cutters above 7mm. Consider also the cost of the cutters as that could make up the differenc. 1/2" router cutters have a large market, hence they are cheap. In addition the power from the spindle (roughly) decreases linearly from maximum power at around half rated speed to zero at zero rpm. You'll probably never use 1.5kW, let alone 2.2kW, but because of this relationship it's important to have the higher rated power to maintain enough power at low speeds.
Hence you will find it harder to use the 1.5kW spindle at low speeds - i.e. harder to cut steel or drill aluminium.

3) The VFD will let you set whatever speed you want - it's the control algorithm and ratings of the spindle that dictate how fast the spindle will run. The 8000rpm minimum you read might have been referring to the air cooled spindles which cannot be operated at low speeds since the fan would not provide sufficient airflow to cool them.

JAZZCNC
04-08-2012, 12:43 AM
Excellent Wilfy, you have totally understood where I am going with my questions!

Geoff so have WE but your blinded by the desire to build cheap.! . . . . Read the thread Wilfy posted and just look at the wasted money with the end result being he's started over again doing it the way it should have been done first time.!! (Actually he's over done it for wood, with some expensive components capable of far more than the design can handle.!!)

I foreone are just trying to help save you money by not wasting money on inferior or below par components. ?

Regards Kress VS WC: You say the 100 difference buys 4 steppers.? . . . I say what's the point if the spindle's dead within a few weeks or months and the machine can't cut.!!. . . . Now those steppers are very expensive paper weights.!!

Don't look at the NOW think of the future.!!

m_c
04-08-2012, 01:22 AM
I quite liked that first router in Wilfy's link. It shows what is possible with wood, however I suspect the guy always planned on redoing it, and alot of the components were picked for ease of building rather than cost, as it wasn't really a cheap build component wise.

If you want to cut costs, and you've got the time/motivation to redo things, use wood for large flat sections, but design it so you can then replace with aluminium as time/money allows. And spend the money saved on making sure the other parts are good quality and upto the job. From what you've said, you're not aiming for high accuracy, and you are realistic about what you aim to achieve, so go for it.

BikerAfloat
04-08-2012, 02:40 PM
Hi All,

I apologise if my thanks to Wilfy caused any offence, it was not my intention and this is one of the traps I was hoping to avoid falling into.

I have never liked text conversations, they are so easily misconstrued unless your writing is 100% all of the time. This fact has stopped me from posting forums intil now, where my need for advice outweighed my reluctance to join in.

I have not once doubted anyones ability or good intentions and unless I have inadvertantly missed someone, thanked you all for your input as it has been given.

As my Mental Health stands focusing on this project is a challenge in itself, putting my ideas forward for assement was a massive step for me. Severe depression stinks, please trust me when I say I am battling my irrational needs for avoiding people and my rational needs for moving this project forward. If I am overly defensive it is a function of where my head is at!

I hope it is clear from my background, I am (just about) capable of realising this machine is far from ideal and that I have chosen this path for very good reasons. As you know my 2nd post included mature design drawings for this machine. These are a result of many many hours research, hard work, careful thought and very seriously considered compromises in performance vs cost.

Can we please leave it as a "given" I accept that "more money = a better finished product" and keep the advice to that which will allow me to make this project come to fruition.

Sorry Jazz, but I am not "Blinded by my desire to build cheap". The budget is a cold hard reality.

With regard to the build log link Wilfy sent us. I was thinking that maybe I was going to be forced to abandon starting with a router by seeing something exciting like a video of one exploding, or maybe something slightly less dramatic but equally final!

Given the guys facilities and his obvious abilities and ambitions, I do not understand him starting with a Hose pipe & Jubilee Clip build at all! It came as no surprise to see him making upgrades with the finished tool and while I did not keep an eye on the time frame of this post, very soon afterwards abandoning the project. I can only assume he had a significant change in circumstance, as "one minute" he is explaining about his lack of funds and the next a big shipment of shiney things appear! The expense he has incurred from his router experience alone would pay a big chunk of my total budget!

Ok, Next post.... The Spindle

Cheers,
Geoff.

JAZZCNC
04-08-2012, 03:14 PM
Sorry Jazz, but I am not "Blinded by my desire to build cheap". The budget is a cold hard reality.

Then the cold hard reality is that you can't afford to build this machine yet.! . . . For only a few dollars more the overall savings and performance will be considerable.!

Anyway I'll say no more other than to wish you well.!

Edit: PS: Personally You didn't offend me and don't take my comment wishing well has meaning I won't advise or offer help.!! Most certainly will and happy to do so.

mocha
04-08-2012, 05:10 PM
A very interesting build log. Shed loads of work and the scary amount of 7-10 thousand euros went into getting to the current position!

Interesting too that the first design was 16th December 2009 and the mark 2 design 16th January 2010! (That cost him 1500 euros)

The hardest part of my build has been the waiting until I can afford to do it.

BikerAfloat
04-08-2012, 06:56 PM
Then the cold hard reality is that you can't afford to build this machine yet.!


I know I can't, but I can't afford to not do it even more! :cower:

audioandy
04-08-2012, 07:08 PM
Geoff

Pm sent

wilfy
04-08-2012, 08:00 PM
Guys just to note, the main reason I linked that post was to prove 2 things, the first thing was to state the obvious that starting out with a router will only lead to water cooled spindle. The second thing is more subtle, look at how much money the guy wasted, if he had been a member of this forum and listened to the advice of guys here, he would have saved a lot of money

Jonathan
04-08-2012, 08:06 PM
The second thing is more subtle, look at how much money the guy wasted, if he had been a member of this forum and listened to the advice of guys here, he would have saved a lot of money

I'm sure he's going to waste more yet. Prime example is the ballscrews he used. Only 5mm pitch over than length, plus he's used expensive ones not cheap ones from china so no excuse.

Ricardoco
04-08-2012, 08:29 PM
I'm sure he's going to waste more yet. Prime example is the ballscrews he used. Only 5mm pitch over than length, plus he's used expensive ones not cheap ones from china so no excuse.

Hey Jonathan, the 5mm pitch over that length, is ithat likely to cause him problems, I only ask because im building a similar size steel machine at the moment
.

Rick

Jonathan
04-08-2012, 09:05 PM
Hey Jonathan, the 5mm pitch over that length, is ithat likely to cause him problems, I only ask because im building a similar size steel machine

Not sure what length he's actually used, read about 5 pages and got bored, so I'll just comment in general...
As a rough guide any axis about 1m will benefit from using greater than 5mm pitch and over about 1.5m rotating nuts become more economical. The reason is by going to 10mm pitch the RPM of the screw is halved for a given feedrate, so if the limiting factor is the critical speed (speed at which the screw starts whipping) using a 10mm pitch screw will get twice the feedrate of if you had used 5mm of the same diameter.

He's been forced to used driven nuts no doubt due to the critical speed being too low over that length, however he's starting with the wrong ballscrew and has made the shafts on the mounts far larger than necessary which will add a huge amount of inertia to the system so I'm not surprised they've not made much difference.

The other problem is using 5mm pitch has forced him to use 25mm screws, which is a massive disadvantage since their inertia is 2.44 times greater than for instance using 20mm diameter. This will greatly reduce the possible acceleration.

I believe you're X-axis is 8'? If so with sufficiently powerful motors (Nema 34 ideally with mains drivers) you could use RM2510 ballscrews and get up to about 5m/min which is nothing special, but adequate. Alternatively RM2020, which is significantly more expensive, which will get up to about 8m/min and you would probably still need Nema 34 motors but may get away with cheaper drivers. Either of these configurations would excel with a driven nut and 3Nm Nema 24 motors.

BikerAfloat
04-08-2012, 09:24 PM
Hi All,

I'm after drawings for both the 1.5 & 2.2 kW Chinese spindles if someone has them, could you post them for me please?

Cheers,

Geoff.

Ricardoco
04-08-2012, 09:55 PM
Hi All,

I'm after drawings for both the 1.5 & 2.2 kW Chinese spindles if someone has them, could you post them for me please?

Cheers,

Geoff.
6509


Thats the best i can do so lets hope someone else has the other...

Jonathan
04-08-2012, 10:08 PM
They do vary a little. Just had mine out of the spindle mount anyway as I'm investigating dynamic balancing and it's slightly different to that drawing. The main body is 80mm diameter for 200mm, then 11mm more at 68mm diameter, then the chuck protrudes by 39mm. When a tool is installed you need to add about 8mm to the length to account for the collet nut. It shouldn't make much difference to the Z-axis design...

Ricardoco
04-08-2012, 10:20 PM
They do vary a little. Just had mine out of the spindle mount anyway as I'm investigating dynamic balancing and it's slightly different to that drawing. The main body is 80mm diameter for 200mm, then 11mm more at 68mm diameter, then the chuck protrudes by 39mm. When a tool is installed you need to add about 8mm to the length to account for the collet nut. It shouldn't make much difference to the Z-axis design... The drawing has a few innacuracies in it and in fact is the same size as yours i suspect, take a look and see if you can spot the mistakes..lol

Ricardoco
04-08-2012, 10:34 PM
6511

Thats better..

Robin Hewitt
05-08-2012, 01:10 AM
If strapped for cash you can buy a straight shank ER collet chuck and a couple of bearings on ebay for very little, then add whatever motor you can turn up. If you want to cut aluminium or steel, rather than vapourise it, 2-3000 rpm is good.

BikerAfloat
05-08-2012, 09:43 AM
Hi Robin,


If strapped for cash you can buy a straight shank ER collet chuck and a couple of bearings on ebay for very little, then add whatever motor you can turn up. If you want to cut aluminium or steel, rather than vapourise it, 2-3000 rpm is good.

I had been thinking along those lines as a serious option for the future, there is a thread I have seen where a gentleman is doing just that (Ah found the thread again: http://www.mycncuk.com/forums/diy-project-building/445-diy-spindle-design.html). Prior to seeing that I was struggling to work out how to do the collet and spindle. I was totally unaware of the ER spindles! I probably have a suitable motor somewhere in my Dad's shed.

Thank you very much for the suggestion.

Cheers,

Geoff.

BikerAfloat
05-08-2012, 02:27 PM
Just found this on eBay @ Tousdiamants Diamond milling machine W12 collet spindle ( schaublin aciera sixis | eBay (http://www.ebay.co.uk/itm/Tousdiamants-Diamond-milling-machine-W12-collet-spindle-schaublin-aciera-sixis-/200800718355?pt=LH_DefaultDomain_3&hash=item2ec0a7ce13)

6512 Already @ 82!!! an unknown quantity, so not going to buy it. However this idea seems is very much do-able.

The link I posted earlier is using an RC plane motor, These are very very grunty for their tiny size, but are still in the 10s of thousand rpm range.

A quick look at "typical" 1/4HP (180W) single phase motor on ebay gave me 220mm dia (way too big to be practical) and is as heavy as a very heavy thing. Not after massive depths of cut as max material thickness I envisage in Ally is 30mm* and maybe 2mm (maybe 5mm) in steel.

*First job will be single piece motor mounts when I can trust myself and the machine!

A 24v 200w electric scooter motor:

6513

e scooter electric 24v 200w Motor belt drive escooter | eBay (http://www.ebay.co.uk/itm/e-scooter-electric-24v-200w-Motor-belt-drive-escooter-/300600076948?pt=UK_Sporting_Goods_Scooters_LE&hash=item45fd292a94)

It has a what seems like a "too good to be true" new price of just 26 on eBay and from the size of the wires is relatively diddy. It gives 2700rpm, which is in the right ballpark now! Presumably these are man enough, they lug humans around!

Main concern is with Duty Cycle, any thoughts?

So...

ER20 Long shank collet roughly 20
2 x 6004 2RS Bearings 10
Scooter motor 30
24V 10A Power supply roughly 30
Some pulleys & a belt say 30 all in (Might even have some suitable somewhere in Dad's shed
Might have material for holding bearings and making motor mounts

Downside, simply cos I wanted to do this myself...

Would need someone to do the machining for me.

With stepped pulleys, I guess wiring the motor direct to Power Supply with a switch and a link to the machine E-Stop would be fine.

120 say 150 tops, definately do-able, especially as it would be close to "best practice" for metal.

Obviously collets to get as well, but since it's ER20 only 1 set needed if I go 2.2kW WC eventually.

Any ideas for a 240v motor, minimum power and so on?

or is the Scooter motor idea viable? Bearing in mind Steppers are also often run this way!

Cheers,
Geoff.

JAZZCNC
05-08-2012, 03:46 PM
I'd look for a DC tread mill motor far more powerfull with good duty cycles.!

BikerAfloat
05-08-2012, 04:37 PM
What an excellent idea Jazz

Plenty on eBay for <30 I can rob power supplys, motor & speed control from a complete machine!

Gonna check Freecycle to!

Cheers,
Geoff

BikerAfloat
15-08-2012, 10:27 PM
Hi All,

After some more reading and some hard thinking, here is the Mk2 machine (progress so far):

6608

Went back to the drawing board completly, re-assessed the space and scaled the machine to what I think I can get away with, rather than basing the machine on the A3ish size previously.

Ive used 5mm Wall Steel RHS as that should be good for the tapped threads to hold down the rails.

Bottom Cross members: 120x60x870
X Rail Supports: 120x80x900 with 900mm SBR25 Supported Rails
Ballscrew Supports: 80x40x220
RM1605 Ballscrews on all Axissss.
Gantry "Feet": 80x40x200 5mm Wall Steel RHS with 2 x SBR25 Bearing Blocks
Gantry Cross Member: 80x80x870 with 2 x 700mm SBR25 Supported Rails, top and bottom.
Y Axis Ballscrew Supports: 10mm Thick Steel plate
Z Axis Plates: 12mm Thick Steel plate
Z Axis Rails: SBR25 Support rails 300mm long

That makes travel roughly X=780, Y=480, Z=100

Y & Z are driven by 2:1 Belt drives, for the X Axis, I am considering a single belt, 3 pulleys and 2 idler bearings also at 2:1 reduction

That's a 2.2kW watercooled spindle on the Z, though I'm also looking at the Treadmill motor option for low rpms. Just waiting for a suitable treadmill motor to appear on eBay!

Problem with this machine is I'll have to "borrow" a mates workshop to build the frame and pay someone to make some of the other components as they go beyond my skills and equipment, ho hum, not the original plan, but I'd like to build just 1 machine and have it last me.

As you can (probably) see in the image, the Spindle comes outside the X Axis, I have left this as it gives me good travel over the steel box which I plan to use for a base for machining metals.

Most likely welded construction, though bolts still hold some appeal for maintaining a "I built it myself" perspective...

... Just noticed I will have to bolt on the Y axis leadscrew/motor mounts, otherwise I can't get the leadscrew in!

BikerAfloat
21-08-2012, 11:33 AM
Hi All,

Was wondering if anyone has seen my last post, been up for 4 days now. I'd like to know if I'm going in the right direction before spending any more time on the drawing?

Cheers,
Geoff.

wilfy
21-08-2012, 12:34 PM
Hi All,

After some more reading and some hard thinking, here is the Mk2 machine (progress so far):

6608

Went back to the drawing board completly, re-assessed the space and scaled the machine to what I think I can get away with, rather than basing the machine on the A3ish size previously.

Ive used 5mm Wall Steel RHS as that should be good for the tapped threads to hold down the rails.

Bottom Cross members: 120x60x870
X Rail Supports: 120x80x900 with 900mm SBR25 Supported Rails
Ballscrew Supports: 80x40x220
RM1605 Ballscrews on all Axissss.
Gantry "Feet": 80x40x200 5mm Wall Steel RHS with 2 x SBR25 Bearing Blocks
Gantry Cross Member: 80x80x870 with 2 x 700mm SBR25 Supported Rails, top and bottom.
Y Axis Ballscrew Supports: 10mm Thick Steel plate
Z Axis Plates: 12mm Thick Steel plate
Z Axis Rails: SBR25 Support rails 300mm long

That makes travel roughly X=780, Y=480, Z=100

Y & Z are driven by 2:1 Belt drives, for the X Axis, I am considering a single belt, 3 pulleys and 2 idler bearings also at 2:1 reduction

That's a 2.2kW watercooled spindle on the Z, though I'm also looking at the Treadmill motor option for low rpms. Just waiting for a suitable treadmill motor to appear on eBay!

Problem with this machine is I'll have to "borrow" a mates workshop to build the frame and pay someone to make some of the other components as they go beyond my skills and equipment, ho hum, not the original plan, but I'd like to build just 1 machine and have it last me.

As you can (probably) see in the image, the Spindle comes outside the X Axis, I have left this as it gives me good travel over the steel box which I plan to use for a base for machining metals.

Most likely welded construction, though bolts still hold some appeal for maintaining a "I built it myself" perspective...

... Just noticed I will have to bolt on the Y axis leadscrew/motor mounts, otherwise I can't get the leadscrew in!


looks ace to me, although i wouldn't know if you'd done anything wrong.. although i cant see your Y axis ballscrew in the picture

BikerAfloat
21-08-2012, 03:38 PM
looks ace to me, although i wouldn't know if you'd done anything wrong.. although i cant see your Y axis ballscrew in the picture

Hi Wilfy, thanks for that, there is no leadscrew on the Y Axis yet, drawing very much waiting for input before I do any more!

Cheers,
Geoff.

Jonathan
21-08-2012, 06:53 PM
I notice you've opted for steel plate on the Y and Z axis. The vast majority of people use aluminium instead of steel since it is so much easier to machine, particularly with limited/basic tools. 20mm is a good size for the Z-axis.

You could make the top Y-axis rail longer (820mm ish?) and increase the spacing of the two SBR25 bearings upon it, so the plate the Z-axis bearings are mounted on would be a T-shape. Although not critical since your Z-axis is already a good size, this would increase the rigidity for little extra cost.

What's the plan for the bed?


Hi All,

After some more reading and some hard thinking, here is the Mk2 machine (progress so far):

6608

Went back to the drawing board completly, re-assessed the space and scaled the machine to what I think I can get away with, rather than basing the machine on the A3ish size previously.

Ive used 5mm Wall Steel RHS as that should be good for the tapped threads to hold down the rails.

Bottom Cross members: 120x60x870
X Rail Supports: 120x80x900 with 900mm SBR25 Supported Rails
Ballscrew Supports: 80x40x220
RM1605 Ballscrews on all Axissss.
Gantry "Feet": 80x40x200 5mm Wall Steel RHS with 2 x SBR25 Bearing Blocks
Gantry Cross Member: 80x80x870 with 2 x 700mm SBR25 Supported Rails, top and bottom.
Y Axis Ballscrew Supports: 10mm Thick Steel plate
Z Axis Plates: 12mm Thick Steel plate
Z Axis Rails: SBR25 Support rails 300mm long

That makes travel roughly X=780, Y=480, Z=100

Y & Z are driven by 2:1 Belt drives, for the X Axis, I am considering a single belt, 3 pulleys and 2 idler bearings also at 2:1 reduction

That's a 2.2kW watercooled spindle on the Z, though I'm also looking at the Treadmill motor option for low rpms. Just waiting for a suitable treadmill motor to appear on eBay!

Problem with this machine is I'll have to "borrow" a mates workshop to build the frame and pay someone to make some of the other components as they go beyond my skills and equipment, ho hum, not the original plan, but I'd like to build just 1 machine and have it last me.

As you can (probably) see in the image, the Spindle comes outside the X Axis, I have left this as it gives me good travel over the steel box which I plan to use for a base for machining metals.

Most likely welded construction, though bolts still hold some appeal for maintaining a "I built it myself" perspective...

... Just noticed I will have to bolt on the Y axis leadscrew/motor mounts, otherwise I can't get the leadscrew in!

BikerAfloat
21-08-2012, 08:12 PM
Hi Jonathan and thank you for your post,


I notice you've opted for steel plate on the Y and Z axis. The vast majority of people use aluminium instead of steel since it is so much easier to machine, particularly with limited/basic tools. 20mm is a good size for the Z-axis.

Opted for 12mm steel for strength and to keep the overhang low-ish (well low within the restrictions of supported rails), I thought I'd keep the aluminium down to a minimum for stiffness. I'll see what the 20mm gains me in reduced overhang, it might be worth a drop in stiffness over 25mm. What size do people tend to go for?



You could make the top Y-axis rail longer (820mm ish?) and increase the spacing of the two SBR25 bearings upon it, so the plate the Z-axis bearings are mounted on would be a T-shape. Although not critical since your Z-axis is already a good size, this would increase the rigidity for little extra cost.

I had considered that, may look at the drawing again, I have to mount limit switches yet and thought the space could take the mountings for them, that was all.

What's the plan for the bed?[/QUOTE]

I am leaving that open in this sketch, but I have plans for several options:

1) A simple MDF bed with 2 layers, support and spoilboard
2) Aluminium (or maybe even steel) drilled and tapped
3) Open to allow a 4th axis to be mounted
4) A removable T Slotted Steel bed across the front cross member
5) Open to allow me to mount motorcycle engine casings on the bench beneath for engraving

Basically I have left it free to see what develops over time.

I'm hoping with the small overall size and the relatively large size of the frame in comparison, it should be up to most of what I can see me throwing at it... Only time will tell.

Cheers,
Geoff.

Jonathan
30-08-2012, 11:00 PM
Opted for 12mm steel for strength ... I thought I'd keep the aluminium down to a minimum for stiffness.

20mm thick aluminium would be just as strong. You will save the difference in price between aluminium and steel from the relative machining difficulty.


I'll see what the 20mm gains me in reduced overhang, it might be worth a drop in stiffness over 25mm. What size do people tend to go for?

I think we're talking on cross purposes - I was referring solely to steel plate, not the rails. However since you've mentioned it - the 25mm rails are much better than 20mm since in addition to being a bit stronger due to the size they also have one more row of ball bearings in the blocks.




I had considered that, may look at the drawing again, I have to mount limit switches yet and thought the space could take the mountings for them, that was all.

Having the machine as strong as you can is far more important than having a convenient place for a limit switch. You'll find somewhere to put them.



1) A simple MDF bed with 2 layers, support and spoilboard
2) Aluminium (or maybe even steel) drilled and tapped
3) Open to allow a 4th axis to be mounted
4) A removable T Slotted Steel bed across the front cross member
5) Open to allow me to mount motorcycle engine casings on the bench beneath for engraving


Although clearly 1) is the weakest it's not a bad idea to use MDF to start with as it will be adequate for most things, makes clamping easier and doesn't kill the tool if you make a mistake.



take a look and see if you can spot the mistakes..lol

[...]

Thats better..

Your dimensioning still doesn't add up. Mine is definitely different to that drawing - size, aluminium piece on front is a different shape, smaller connector.

There's also now 4 bearing spindles readily available - these are 215mm long instead of 200mm.

BikerAfloat
31-08-2012, 05:10 PM
Hi Jonathan,

Thanks for your post,

"I think we're talking on cross purposes..." - Yup my mistook!

I'm going to have to borrow a mates workshop for this build, so I'll be able to work the steel plate almost as easily as the Ally there, so from a rigidity and space point of view I'm plan to stick with Steel plate.

I wasn't aware of the extra row of bearings in the 25mm bearing blocks, that's a good reason to stick with them, the space saving is only 10mm if I went to 20mm rails on the Z Axis anyway.

Cheers,
Geoff.

BikerAfloat
16-09-2012, 01:44 PM
Hi All,

Here are the latest drawings for the machine, it's nearly there, just need some advice on the X Axis belt drive, or more specifically the idler pulleys, I can work something out, but I'd rather go with a tried and tested system. They are currently set at 25mm OD, their construction and size are open to change.

6905690669076908690969106911

I know steel rings like a very ringy thing and some form of filling is in order, I'm pretty sure I wont be able to use epoxy and agregate from a weight point of view, I have to consider the stability and balasting of the boat. I was wondering if expanded foam would act as a dampener, anyone got any experience/ideas?

Spindle shown is Chinese W/C - 2.2kW one, I also plan to have a dedicated low speed job for the harder materials. My supply is currently (Sorry for the pun) limited to 16Amps on the landline - going to have to do some sums to see just what a compromise this will cause. 2200W @ 240v = 9.2 Amps so 6.8Amps left. This means I would have not a lot left for everything else (Fridge, Lighting, 2nd PC!) , Me thinks either a 2nd landline or more likely a generator will be required!

I can pm the sketchup file if anyone would like to check it over, all I really need to know is that the design is buildable, I'm fairly sure it is, but sometimes you can miss little details when you are too close to something.

I'd like to learn the capabilities and limitations of this machine design, I've taken a lot on board for this design from previous posts to this log and from reading other peoples experiences, but there has to be a time when you stick a stake in the ground and this is where I find myself. If you see something is dangerous or impossible please tell me so and I will change it. Otherwise this is the machine I plan to build warts and all.

If the design is doable (Not perfect, but doable) I plan to start buying components sometime in the next week or two. The order I think I'm going to use is something like this:

1) Linear Rails and Bearings - Need this to be sure of the holes I need in the steel.
2) Steel.
3) Pulleys and belts - to make sure of the sizes so I am safe for the Ballscrew Machining.
4) Ballscrews and Bearings.
5) Steppers.
6) Electronics & controller software. 3 choices Planet CNC USB, EMC2 or Mach3(4?) Need to do a feature/cost comparison Gut says Planet CNC as I need a BOB and the software was written to work specifically with their BOB, Head says Mach3 as it seems to be the most used and the little perverted Demon on my shoulder says EMC2, as it's about time I learnt about Linux!
7) Spindle - probably use my hand router to start cutting and pay for W/C jobby and the dedicated low speed one.
8) Additional software for modelling - going to start with the free stuff to get the feel of the machine.

Does this seem logical, are there changes I should make?

Another long post, so I'll stop here and wait for a while before adding any more.

Cheers,
Geoff.

wilfy
17-09-2012, 06:49 PM
sorry i can't add much again, but what i will say is consider emailing the dude your getting the rails and screws off first for a price and pay outside of ebay, this way you will get a better price and while your at it get him to quote you to include and also not include the spindle.. chances are due to combined postage and a big order you may find yourself getting the spindle alot cheaper than anywhere else.. this is certainly my play when the time comes.

also i only just realised your building this machine to work on a boat.. thats just awesome in its own right.

expanding foam is also something i was considering for my build.. it's very cheap and i think it would go some way to take the ring out of the steel as it wouldnt have any air to resonate through the center of the box section

BikerAfloat
18-09-2012, 11:27 AM
sorry i can't add much again, but what i will say is consider emailing the dude your getting the rails and screws off first for a price and pay outside of ebay, this way you will get a better price and while your at it get him to quote you to include and also not include the spindle.. chances are due to combined postage and a big order you may find yourself getting the spindle alot cheaper than anywhere else.. this is certainly my play when the time comes.

Good idea Wilfy, my strategey for ordering bits is based on me funding the job myself, so the spindle is my last purchase, however I am pursuing a couple of other avenues for funding - I am Bi-polar (Manic-Depressive) and it is difficult for me to be employed, hence building the machine to enable me to be self employed. The upside of my illness is the support from the Mental Health team. They beleive there may be some funds to help people like me back to work. If the funds come from there in a lump sum, then I will be looking at making them go as far as I can and that is a good strategy, Thank you for the idea.



also i only just realised your building this machine to work on a boat.. thats just awesome in its own right.


Hee Hee, Home is a 53' Narrowboat, I'll be lossing quite a bit of living area to accomdate this, but if I can keep my costs down by not having to rent a workshop, the the plan for self-employment is that bit more viable.



expanding foam is also something i was considering for my build.. it's very cheap and i think it would go some way to take the ring out of the steel as it wouldnt have any air to resonate through the center of the box section

Glad to hear I'm thinking along the same lines as someone else, makes it seem a more viable idea. Thanks again!

Cheers,
Geoff.

Jonathan
18-09-2012, 12:05 PM
I notice on your design the X rails are the same length of the box seciton. I would leave about 5-10mm clearance at both ends to ensure they lie flat in case the box section is distorted at the ends.

Going by your order;

1) Bear in mind the holes in the SBR rails look like they've been drilled by an ape swinging on a pillar drill - you can sometimes even see the pencil lines which mark where the holes go, so don't expect them to be accurate. Make the frame and gantry then mount the rails to the frame by drilling and tapping one hole at a time until you have them aligned and running smoothly, then drill and tap the rest.
3) I found recently that a local shop is cheaper than getting the pulleys and belts online, plus no long delivery time and additional delivery time to send back the items they got wrong!
6) I reckon try LinuxCNC then mach3 then Planet CNC because clearly if you get on well with LinuxCNC then you've saved a lot of money compared to the other options. If not by all meant buy mach 3. Either way don't expect to learn much if anything about Linux though, since one it's installed it's just like using a program on windows.

Foam is an interesting idea, by all means try it but I don't think it would help that much with resonance. As far as I know the issue is not the 'air resonating through the centre', it's the walls of the steel box section that vibrate. To prevent resonance on the not moving parts you should add mass, or some material with good damping properties which tends to be materials made up of particles which rub against each other to dissipate the energy as heat. Sand covers both criteria, but it sounds like that's not an option.

JAZZCNC
18-09-2012, 04:24 PM
expanding foam is also something i was considering for my build.. it's very cheap and i think it would go some way to take the ring out of the steel as it wouldnt have any air to resonate through the center of the box section

Doesn't work I've tried, it's not dense enough complete waste of money if you do.

By far the best thing is kiln dried sand nothing really comes near for ease of use or cost.

BikerAfloat
18-09-2012, 07:49 PM
I notice on your design the X rails are the same length of the box seciton. I would leave about 5-10mm clearance at both ends to ensure they lie flat in case the box section is distorted at the ends.


Was looking at that, I think I will do that as it gains me some extra working area too, for not a lot more cost.



1) Bear in mind the holes in the SBR rails look like they've been drilled by an ape swinging on a pillar drill - you can sometimes even see the pencil lines which mark where the holes go, so don't expect them to be accurate. Make the frame and gantry then mount the rails to the frame by drilling and tapping one hole at a time until you have them aligned and running smoothly, then drill and tap the rest.


Yes I thought they'd be added manulally after cutting, that is why I plan to drill to suit as you suggest!



3) I found recently that a local shop is cheaper than getting the pulleys and belts online, plus no long delivery time and additional delivery time to send back the items they got wrong!


Not sure in the wilds of Cambridgeshire will be that advanced, but I'll have a look!



6) I reckon try LinuxCNC then mach3 then Planet CNC because clearly if you get on well with LinuxCNC then you've saved a lot of money compared to the other options. If not by all meant buy mach 3. Either way don't expect to learn much if anything about Linux though, since one it's installed it's just like using a program on windows.


I like the Linux price, but it's uncharted waters! And yes I guess I'll be too busy making stuff to learn much! I'm stll very much in favour of the Planet CNC stuff as the BOB and software are less than Mach3 and I believe the USB BOB has some buffering to help with the non-realtime windows performance. Would be best to be able to try all three hands on, or at minimum get a copy of the manuals to compare features & interfaces.



Foam is an interesting idea, by all means try it but I don't think it would help that much with resonance. As far as I know the issue is not the 'air resonating through the centre', it's the walls of the steel box section that vibrate. To prevent resonance on the not moving parts you should add mass, or some material with good damping properties which tends to be materials made up of particles which rub against each other to dissipate the energy as heat. Sand covers both criteria, but it sounds like that's not an option.
[/QUOTE]

Mmmm, as Jazz has tried it without success (Thanks for that Jazz) the foam seems to be a no-no. I will have to see how the boat is when the machine is done. Sand can always be added later if I make the boxes "water tight" from the start. I guess if it is too noisy and the sand becomes a must, I can always use the router to make book cases along much of the other side of the boat. That'll give me an excuse to by more books as they are needed for ballast!

Cheers Geoff.

TrickyCNC
18-09-2012, 08:24 PM
I like the Linux price, but it's uncharted waters! And yes I guess I'll be too busy making stuff to learn much!



I use linuxCNC and as Jonathon says, there is no learning involved on the linux side of things.

You can try it for free. It's very easy to install (just a wizard mouse click install ! ), and once it's installed, it's very intuitive. Linux, is basically the windows desktop, and EMC is an Icon to click on to use it ! no need to learn linux in the slightest :)

Rich

BikerAfloat
19-09-2012, 10:04 AM
I use linuxCNC and as Jonathon says, there is no learning involved on the linux side of things.

You can try it for free. It's very easy to install (just a wizard mouse click install ! ), and once it's installed, it's very intuitive. Linux, is basically the windows desktop, and EMC is an Icon to click on to use it ! no need to learn linux in the slightest :)

Rich

Thanks Rich,

I'll look into it further...

As a user maybe you could answer a question for me (Mach 3 users, I have the same question for you)?

One of the jobs I wish to do with this machine is to engrave motorcycle engine cases, the reason I like the idea of the Planet CNC software is that it has a function where you can scan an un-even surface (in this case engine covers are often convex curves) and the software then allows for this in the Z travel so that the engraving (or cutting) depth remains constant over the uneven surface.

Does EMC2 (or Mach3) have a similar function?

Cheers,
Geoff.

TrickyCNC
19-09-2012, 10:49 AM
not as far as I'm aware (for either).

I've seen the Vectric Aspire trial version can map text onto a 3d surface, but that's a bit pricey.

I'd have thought that was more of a Cam operation than a front end op. ?

Rich

Jonathan
19-09-2012, 11:01 AM
I'd have thought that was more of a Cam operation than a front end op. ?

Yep, either will do it with the right code. Just height map the part using a probe, which should be easy if it's metal as you can use a pointy bit and the part as the switch, then you effectively need to apply that transformation to existing code, or import the pointlist into a CAD program as a surface and use that to generate the code. There's plenty of CAM programs which will do the latter.

JAZZCNC
19-09-2012, 05:29 PM
I've made and engraved quite a few MotoX bike clutch casings. If it's just an engraving then Jonathans way is the best and easy enough to do. Depending on how curved dictates to how dense you need to probe and time taken, thou it's usually a 5min affair has your only needing the curvature not the whole shape etc and the surface area is small.

Also I have a USBCNC card to try but not got round to it yet has the machine I'd like to try it on isn't finished. Will let you know when I do but it won't be for awhile.

BikerAfloat
20-09-2012, 03:17 PM
Thanks Jonathan,

I was wondering if using a tool and the case was possible, thanks for confirming that for me.

Still much reasearch to go software wise!

Cheers,
Geoff.

BikerAfloat
20-09-2012, 03:25 PM
Hi Jazz,

Glad to hear someone else has done this, what software did you use? Software is yet another area that needs much reading, this CNC lark certainly keeps you busy, even without a machine!

Look forward to reading the posts on the USBCNC, will be good to know how it relates to Mach 3/EMC2, which do you use/prefer?

Cheers,
Geoff.

JAZZCNC
20-09-2012, 05:53 PM
I use Rhino for 3D/2D Cad modelling.
Generate tool-paths using BobCAD-CAM for general engineering stuff like machining casing etc and Artcam for other stuff like engraving or signs etc.
Both will do Engraving thou Artcam does it better or should say has better tool-paths. BobCad does the engineering stuff better, again with tool-paths more suited to that type of job.
Both will project tool-paths onto curved surfaces.

Only use Mach3 and know it inside out and it works with great backup and tons of experienced users behind it on the very rare occasions I need help.