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View Full Version : BUILD LOG: Let The Fun Begain, New build on the Table.



Bush Flyer
11-04-2013, 11:28 PM
Hi All,
My name is Mike and I am about to start building my very first CNC router,
I will need a lot of help with this and I hope I can count on you all to help. I will change some of my design to what you tell me but I might reject some and go with my own ideas.
Anyway My main Hobby is building and flying Radio Control Scale models and I hope to make some model kits of planes that I have designed along with Retracts etc to help recoup some of the money that I will be putting into this machine.
Now with this in mind the main thing that I will be cutting is Ply, balsa, and aluminium for the most, But of course I will have to try house signs wooden toy and any thing else.
The rails will be Supported linear rails SBR20-300mm SBR20-650mm SBR20-1100mm with the Bearing Blocks.
And the ballscrews RM1605 - 350mm - 700mm and I will use twin ballscrews - 1150mm This I cannot change as I have them waiting for me on my bench.
Now I purchased some 6082 aluminium for the Z axis which is 20mm thick 330mm x 160mm and I was surprised at the weight 3.4kg.
The first question of many.I was planning to use these steppermotors, Will the Nema23 Stepper Motor 3.1Nm be strong enough to work this ( the weight of aluminium four bearing and a router. ) I was going to use these straight without gearing? I have attached a drawing of the Z axis ( I hope ) to let you see what I'm thinking about.

Jonathan
12-04-2013, 01:42 PM
I advise you read some of the build logs (http://www.mycncuk.com/forums/router-build-logs/) on this forum, as it is evident from the Z-axis design, some of the parts you have chosen and the question you ask, that you would do well to find out more before building this. For example, it's stronger to put the Z-axis rails on the same plate as the spindle and it would have been better to have RM1610 screws for X and Y.

20*330*160*2.7*10^-6=2.85kg, so either your scales are wrong or the dimensions of that plate are greater than specified.

3.1Nm motors will be plenty. Using timing belts and pulleys has numerous advantages, including getting better performance by changing the drive ratio, making it easier to mount the motor and helping with resonance damping. Since it seems you have bought 5mm pitch screws for X and Y, you will almost certainly need to use a 2:1 ratio (bigger pulley on motor) to make the machine run fast enough. Again, this information is nothing new - read a few build logs and you'll be able to answer the questions yourself.

Bush Flyer
12-04-2013, 10:00 PM
Ok my mistake it is 2.85Kg and not 3.4Kg I made the mistake when I converted from 6.283Lbs to Kg.
Right now we know I'm an idiot I have changed the design round to the rails on the same plate as the spindle, The reason I did it the other way round was there would be less weight for the stepper motor to lift, I also have a question about the gearing, If I used a 2:1 will I not lose torque but gain the speed from the stepper motor?
Here is my new drawing see what you think, I would have liked to put the two bearing blocks in line with the gantry blocks but i would lose a lot of travel, Anyway how high should I make the bottom of the Z mounting that holds the router from the table. 8737

Ross77
13-04-2013, 01:37 AM
Hi,
As Jonathan said this is all covered in most of the previous builds. Revised plan is much better but you could gain a bit more rigidity by moving the lower block down to match the end of the rail as your z axis blocks look a little close. The z axis is the weakest part as it is a cantilever and will flex the most, A larger distance between the blocks will also reduce the bending moment on the y axis (rotational lever arm effect) What travel where you looking for?

The z axis blocks don't have to be in line with the gantry blocks and it might be worth centralising them on the plate so the bottom of the router plate is in line with the bottom y axis beam as that will mean you can lower the gantry sides (whilst retaining the same clearance)to reduce the force on the x axis bearings.

My comments are only to help maximise the performance of the parts you have and are not a critisim of your design. Happy building

Edit. whilst supported rail is stronger with regard to the rail, the bearing is weakened by not completely wrapping around the bar therefore the bearings have reduced strength when pulled away from the rail , this is easily solved by mounting the rails back to back, or in your application on top and bottom rather than on the side. For example in your sketch when the gantry moves to the left the z axis (due to cutting force) will rotate about he lower bearing on the y axis and try to push the top bearing (strongest direction) how ever when the gantry moves right it will still rotate about the lower bearing but now will be pulling on the bearing which is the weakest direction.

Again this point is just a way of maximising the machine strength by design and I'm not saying that the method you have proposed is not good enough as it is probably more then adequate for most uses but my option just increases strength for free....

Height of the gantry needs to be as lower as possible but allow for the max depth of you work + how deep you need to to cut. for example if you work piece is 50mm and you want to cut all the way through you need to allow at least another 50mm for the cutter + shank and collet so say 125mm.

Bush Flyer
13-04-2013, 06:51 PM
Hi Ross77
Right here I am again with the Mk10 drawing of the Z axis, I may see one or two other ways of doing this but I thought I would let you see where I am at this point.
I have about roughly 120mm of travel in the Z axis.
Now about the height from the bottom of the router mounting to the table top. Do you mean that would be 125mm?

8755

Ross77
13-04-2013, 10:04 PM
Yep that looks good. Mk10? so you have only just started then:friendly_wink:

I would increase the distance between the y axis rails to match the z axis plate to increase bending and torsional resistance.

If you have mounting clashes with the blocks then widen the plate, it would be best to make any compromises on the y axis side of things as this is more forgiving than the Z axis.

Yes I did mean 125mm from the bed to the router base. Is that not what you were asking?

Bush Flyer
14-04-2013, 09:10 AM
Thanks Ross77 yes that is what I needed to know, I was just double checking Before making any more adjustment. I appreciate your help.

Ross77
14-04-2013, 03:24 PM
Just thought I'd better check but the 125mm was only an example, actual value will depend of your router collet and cutter length.

What router/spindle are you using? can it be fixed at the top as well? as the L shaped mount is also a bit weak.

Bush Flyer
14-04-2013, 07:48 PM
I have now reinforced the L shaped mount. Its now braced right to the top now.
The router that I will be using is the Kress 530 with a 3.175mm and a 6.35mm collets and I was going to get the mount from CNC4YOU.
Here is the latest drawing of the Z axis.

8782

Bush Flyer
21-04-2013, 01:23 AM
Here are the final drawings
8804880588068807880888098810

Robin Hewitt
21-04-2013, 11:48 AM
Here are the final drawings


No they are not at all final, they're still crap :very_drunk:

Look at the distance from the tool tip to the bearings above. 3 miles is too much.

Find a good solid cardboard box. Remove front and back. Try standing something on top.

When you figure out how to stop it collapsing, go back to your router drawing and try again.

Ross77
21-04-2013, 08:13 PM
No they are not at all final, they're still crap
Harsh but fair eh Robin.

I would agree that the gantry sides are way to slender. You either need to reduce the height of the y axis or thicken up the side plates with some of that profile section. Having now seen the whole design I would reiterate my earlier comment about increasing the distance between the y axiz rails as that will reduce the torsional force on the gantry sides and also give a better ratio of supported to unsupported plate (not sure if that's the best way to describe it?)

The Z axis is way to complicated , get rid of all the blocks and wedging plates. i.e. make the bottom plate as one piece that bolts to the bearing and is also the spindle mount. Do the same with the top plate and make it bolt to the bearing and be the ball screw mount. this will make it lighter, stronger and much easier to build.:smug:

Keep at it, as its worth getting right before you start building.

Bush Flyer
22-04-2013, 09:48 AM
OK I give up and have deleted all drawings to start again, But before I start with a new drawing please can you send a quick sketch of your cnc or a picture as I did not under stand what you mean about the bottom plate as one piece that bolts to the bearing and is also the spindle mount, Remember I have no machining ability so I will be buying the aluminium cut from the supplier at 20mm thick and cut to size as I am disabled and could not hacksaw 20mm thick aluminium plate. But I do have a drill press. I Have been copying some designs but have been adding some extra bracing etc. So now I have a blank screen on my computer and before I start again it would be nice to see your CNC or where to find your build to give me some help in the design.

Robin Hewitt
22-04-2013, 01:49 PM
OK I give up and have deleted all drawings to start again

Oops, lets not over-react, don't empty that recycle bin quite yet. But you are making a newbie mistake :frog:

There is no set way of doing this, best way depends on what you have to work with and what you are trying to achieve.

The newbie mistake is guessing that at some nebulous time in the future you will want the gantry to clear 6".

In the real world you do 99% of your cutting in the bottom 1" because that is the length of your average router bit.

Get it wrong and 99% of your cutting is done at full tool extension and the machine tries to shake itself to bits.

Q1: What height does your gantry need to clear?

m.marino
22-04-2013, 03:49 PM
Having designed and working with a machine with the C style gantry I would strongly suggest IF possible to move the C so that the Screw is behind it to protect the screw from swarf (I have to clean mine often). While you really do need to increase the rigidity of the gantry supports, that can be done a couple of different methods.

1) go to extrusion for the gantry sides (the solution used on my machine)
2) Increase thickness and add full running ribs to add even more rigidity
3) Increase thickness even more then above and add partial supports to help transfer force to the plate you use for the x axis rails

I would not only go through the build logs here but also go to places like , shopbot, CAMaster, MultiCAM, and a few others and look at those machines and their designs. One of the items about hobby CNC machines is they are often over built. It is not a bad thing but it can add to the expenses without reason. The use needs to be taken into account in the design. Building a machine that can cut steel for doing MDF is over kill and funds used poorly.

Good luck with the design and keep posting, don't mind the gruff from any of the folks here, it is normal and you just take on the information and let the rest go.

Michael

Jonathan
22-04-2013, 06:10 PM
Having designed and working with a machine with the C style gantry I would strongly suggest IF possible to move the C so that the Screw is behind it to protect the screw from swarf

That can be done, however you need to be careful not to have the ballscrew far from the Y-rails and spindle, otherwise the stiffness of the axis will be greatly reduced.

Ross77
22-04-2013, 07:20 PM
Apologies if my comments seem harsh, I am only trying to help you make your machine as strong as possible and easier to build.

My Machine is still on the drawing board and is way different from yours anyway. if I get time I will sketch some thing out for you.

I've attached a design I started 4 years ago but abandoned as I needed a stronger machine, you might be able to adapt afew bits. The z axis has the one piece top and bottom plate I was talking about and also the raised x axis rails might suit your design as it makes the gantry shorter and still gives a good depth of cut. Its not a finished design so I know its not perfect.



That can be done, however you need to be careful not to have the ballscrew far from the Y-rails and spindle, otherwise the stiffness of the axis will be greatly reduced.

That was my thought as well, you would place the ball screw under unnecessary load by having the link bar go around the beam to the z axis. better to cover the ball screw with bellows. Or if you make the c section deeper to increase the y axis rails then the ball screw could be moved to the top so out of the way of chips.

Happy building

Bush Flyer
26-04-2013, 12:51 PM
Hi all,
Here is my new drawings for my 1100mm X 700mm X 300mm CNC, the only thing that I kept was the bed, everything is new from there.
I lowered the height of the gantry the Z axis from 125mm to 55mm (that's back to the height that I had my very first drawing) from the bed that should let me put a thin mdf board as a sacrificial board. The travel in the Z axis is 110mm.
The gantry sides are made out of two 20mm thick plate aluminium which will be bonded and bolted together, the first one is solid the second one will be lightened. The Z axis will also use 20mm plate aluminium. The backing on the Y axis is 12mm plate aluminium bolted to Aluminium Profile Extrusion. And the X axis can easily be stiffened buy adding more Extrusion to the Bed if needed.

Ross77,
Thanks for letting me see your drawings, and I have seen this design before and dismissed it as being to difficult to build. The welding part is easy but to make it accurate would mean a lot of shimming, as you know welding one side of the metal joint twists the steel one way and when you weld the other side of the joint it will pull it back again. I am not longer able to Cut and grinding steel due to now being disabled. But I do like the Z axis and I would like to see a photo of your machine.

8846

Swarfing
26-04-2013, 06:41 PM
A quick thought!

Flip the 'Y' axis (top to bottom) arrangement over and add another plate to the back to mount the ballnut and you will always have a nice clean screw :thumsup:

Ross77
26-04-2013, 06:49 PM
Looks good mate. are you happier with this as well?

Whilst myself and others could carry on making suggestions to tweek if further I think you have got to the point of a build-able machine, without going into calcs you have gone as far as you can.

The only point I would make and it is minor and that is that you might need to add additional support to the top of the X axis bearings to stop them opening up due to the weight of gantry, placing the rails and bearings on their side will improve load capacity but some of the cheaper bearing holders can give and open up the bearing.

I apologise for misleading you with the table distance as I presumed you meant with the z axis at the top of its travel. I see from your drawing you are talking about it a full extension.


I have seen this design before and dismissed it as being to difficult to build
yep thats one of the reasons I abandoned it, cheap but difficult to build. I was mainly showing it to you for the rail orientation.


The welding part is easy but to make it accurate would mean a lot of shimming, as you know welding one side of the metal joint twists the steel one way and when you weld the other side of the joint it will pull it back again

The design was actually for Ali sections and they would have been bonded with epoxy and riveted for good measure. that way no distortion due to welding.

I never got around to building it so no photos I'm afraid.

Ross77
26-04-2013, 06:56 PM
Flip the 'Y' axis (top to bottom) arrangement over and add another plate to the back to mount the ballnut and you will always have a nice clean screw

where's the fun in clean? yes you can do that but moves the ball screw away from the Z carriage and reduces rigidity and can lead to racking or binding of the bearings the extra distance can mean the alignment would be a mare as well.

Edit. thought id seen that mentioned before! just realised it was this thread, so same as Jonathan's answer

Swarfing
26-04-2013, 07:18 PM
Edit. thought id seen that mentioned before! just realised it was this thread, so same as Jonathan's answer

There you go great minds think alike. The distance is minimal and would not make any noticeable difference. As for binding then you need to make allowances in the bolt holes so that you have adjustment

Ross77
26-04-2013, 08:40 PM
Hi Paul
yeah I agree that it probably wont affect the performance to much but without going through all the calcs and then changing/ widening bearing spacing to compensate then it is best left as it is. remember this is being built with a pillar drill so ease of fabrication and also dimensional tolerance is less than parts made on a mil or cnc.

the binding is as a result of the lever arm of the system. the original set up was Bearing-Ballscrew-Load so the ballscrew can control the load directly. moving the ball screw back results in Ballscrew-Bearing-Load so the ball screw has to work through the bearing to contol the load and vice versa, the load is transmitted through the bearings before the ballscrew can control it. Under sudden loads this can cause the system to rotate around the bearing and as open linear bearings have clearance they could bind or cause premature wear.

Again it can be designed out but I think it will be easier to just clean the ball screw

Swarfing
26-04-2013, 08:51 PM
Sorry Ross in this instance i would have to disagree. Swapping it over as i said would result in the ballnut being roughly in the same position, as the plate showing on the 'Z' could be set further back still. For this type of build it will work absolutely fine. Have a look around the forum with such a design and ask how they are getting on ;-)

Bush Flyer
26-04-2013, 09:29 PM
Its good to know that I'm heading in the right direction, and I am happy with the progress so far.

Jonathan
27-04-2013, 01:28 AM
Moving the ballscrew, whilst not disastrous, hardly gains anything. All you're gaining is some protection for the ballscrew from swarf and there are plenty of other ways to do that - for example adding seals or bellows. So even if the difference to the overall machine due to the loss in rigidity is small, you're doing this to correct a problem which is also very small since it's clear that swarf on the ballscrew is also only a small problem. I recall Jazz saying he'd worn out his ballscrews from letting the swarf pile up on them over a few years, but I've not come across anyone else who has had a ballscrew (or nut) fail for that reason.


For this type of build it will work absolutely fine. Have a look around the forum with such a design and ask how they are getting on ;-)

Having the ballscrew on the back on my machine has crippled the stiffness of my Y-axis and although the distance is greater, that shows how the effect can be significant.

Bush Flyer
27-04-2013, 07:38 AM
When I am finished with a tools I am probably OCD about keeping tools clean and put back ready for the next time, It's the same when building a new RC model before finishing for the day I will tidy up and put all tools back where they come ready for the next time, and I have always been like that so keeping the ball screw clean will not be a problem.

Swarfing
27-04-2013, 10:20 AM
Having the ballscrew on the back on my machine has crippled the stiffness of my Y-axis and although the distance is greater, that shows how the effect can be significant.

Correct Jonathan yours was a huge distance from centre hence your issue. Switching would save a lot of hassle having to sort extras like seals and way covers etc. My suggestion was a sound one but the choice is yours of course. BF your design is a good one i would like to point out and will work great without the changes so well done. Building these things is a costly venture and you spent the time listening and looking at what works already. Mine is no way near as good as what you have so you should be in a good place.

Ross77
27-04-2013, 11:25 AM
Sorry Ross in this instance i would have to disagree

No need to apologise, the more opinions Mike gets the better.



Swapping it over as i said would result in the ballnut being roughly in the same position,

Yes but it would need a link arm or bar to connect back to the bearings hence lever arm. It just seems odd to me that people use ball screws to rid of backlash to 0.01mm and then mount them in systems that deflect more than that.

I still agree with Jonathan and don't see why you would risk compromising machine ridigity just to keep a ball screw clean, that's what guards are for :chuncky:

Any way i think this point has been laboured enough and mikes happy to keep his tool clean......

Swarfing
27-04-2013, 11:32 AM
Yes but it would need a link arm or bar to connect back to the bearings hence lever arm.

Mmmm! not sure what you mean here? If you are making a box to encompass the supporting rail then you are actually increasing rigidity. The bearings will be supported both sides of the fence so to speak so can not for the life of me see how it is worse? the ballnut will still be roughly in centre and mounted on the backplate. I really don't see what there is not to understand here.

Ross77
28-04-2013, 07:00 PM
Mmmm! not sure what you mean here?

Ok better explain myself in case I'm wrong. :nevreness:

Just to make it clear thought that its only because open bearings and supported rail are being used with a small bearing centre to spindle nose distance ratio. Ideally the bearing centres (on plan) should be increased but given Mike has already redesigned it a few times I didn't want to offer any more changes without justifying them with calcs.


If you are making a box to encompass the supporting rail then you are actually increasing rigidity.

Yes but its not so much the bearing mounting but the bearings themselves, open bearings can have quite a large radial clearance (10 to 50 micron), with the current set up and using a conservative 10 micron clearance (could be to 50), 100mm bearing spacing and 200mm spindle distance that results in 39 micron of free movement at the spindle. moving the ball screw the other side increases this to 51 micron.

This is free movement just to take up play, if you add any deflection due to load then this will obviously increase further. for cutting Ali the open bearings can run close to the max load capacity and as rigidity is a function of imposed load and load capacity then deflection will be high.

On the face of it 10 micron is a very small amount but remember this is only One element and doesn't include deflection in the part. if you lose 10 micron at every junction then it all adds up to a considerable amount.

Any way that's my take on it!

Swarfing
28-04-2013, 07:17 PM
Ross i did say that the plate could be moved further back. In this design there is no reason why the ballnut could be more central and the spindle moved closer to centre. There is no need to have the nut pushed further away from centre.

Jonathan
28-04-2013, 07:44 PM
Ok better explain myself in case I'm wrong. :nevreness:

I thought your first explanation was good, but the latest one is even clearer. I agree with the 39-51um figure and as you say it's likely to be more. Any compromise like this will reduce the stiffness of each element. You can analyse the stiffness of the overall machine as springs in parallel, so if you reduce one a very small amount it's not likely to make a tangible difference, however if one is reduced substantially such that the stiffness is lower than other elements, then that will dominate the system, causing the overall stiffness to be low. This means compromising one part can waste money you've spent on other quality (stiffer) parts. An extreme example would be using profile rails on two axes and unsupported rails on the other. In that instance changing the profile rails to supported rails isn't likely to make a difference, since the weak point would still be the unsupported rails. Similarly, 'making a box to encompass the support rails' wont make much difference, since that part of the assembly is already at least an order of magnitude stiffer than other parts.

You can get the ballnut in a more optimal position with the current design - it doesn't have to go behind to do that. Similarly the current design could easily have a 'box to encompass the supporting rail' added.


Switching would save a lot of hassle having to sort extras like seals and way covers etc.

Just stick a 15mm shaft seals, like these (http://www.bearingstation.co.uk/products/Oil_Seals/Oil_Seal_Metric/Oil_Seal_ID_11_-_20mm), either side of the ballnut and the swarf is wiped off easily. They're working well for me and not showing signs of wear, although admittedly I've not been using them for long.

Ross77
28-04-2013, 08:01 PM
Ross i did say that the plate could be moved further back. In this design there is no reason why the ballnut could be more central and the spindle moved closer to centre. There is no need to have the nut pushed further away from centre.

Paul I think we must be looking at different drawings:friendly_wink:

If you look at the Z axis drawing in post #18 there is barely enough room to flip the plate over. if you then centralise the ball screw you will have to move the Z axis assembly further away, making the situation much worse.

As I said there are other more pressing issues with the design but as the parts are bought and he wants that size working envelope then there's not much that can be done other than maximise the other components. Another reason for not moving the ball screw is that despite the large plate on the back the y axis could still twist if Mike decides to cut larger pieces of Ali. with the ball screw in the front it is a simple case of widening the y beam to increase its torsional rigidity.

Anyway I think we will just have to agree to disagree on this one.:beer: We all have different ideas and its up to mike to decide as ultimately he knows what is needed from the machine.

Bush Flyer
18-05-2013, 02:20 PM
Right, I have made one small change to the Y axis to tie it all together. So no more changed till it is built. I ordered some 6082 aluminium plate and have started to construct the Z axis.
I can only do a little at a time before the pain is to severe and I have to stop, It will be a slow build but I will get there. Anyway one drawing of the change and two pictures to keep you going.

Ross77
19-05-2013, 11:05 PM
looks like some good progress Mike. that back plate will help stiffen it all up.

glad all the comments didn't put you off. keep it up

Bush Flyer
28-05-2013, 03:09 PM
Ok here is another part done I had to cut 3mm off the aluminium plate, as they came to large. Now the only way I could cut the 3mm off was with a hand held router and a M6 end mill with the plate held in a wooden jig. That was hard going. Anyway with stops to rest I did start to assemble the bed.

897589768977897889798980

robump
29-05-2013, 09:01 PM
Looking really good. Any estimations on how much you think this project will cost?

Just wondering.... Where did you source the aluminium extrusion from? Thanks

martin54
30-05-2013, 01:00 AM
Bit late now but a chop saw would have been a good investment for you if you have problems using a hacksaw.
With the right blade you could have cut all the aluminium both plate & profile yourself which would have made things a bit easier, plus it would also be handy for cutting aluminium to size before machining it once the router is up & running.

Bush Flyer
30-05-2013, 10:18 AM
Looking really good. Any estimations on how much you think this project will cost?

Just wondering.... Where did you source the aluminium extrusion from? Thanks

To get it up and running I hope it will not be more than 1500. I tried to work out what It would cost then added 22%, I cost the bolts at about 40 but it has cost 59 in bolts so you need to add about 22% to what you think it will cost I have done this with everything that I have made and it's stood me well. It will always end up at the higher price.

Bush Flyer
30-05-2013, 10:20 AM
Another picture got finished counter boring the X axiz end plates with a bit of luck I will get them bolted on to the frame today.

8985

Bush Flyer
30-05-2013, 03:15 PM
Bit late now but a chop saw would have been a good investment for you if you have problems using a hacksaw.
With the right blade you could have cut all the aluminium both plate & profile yourself which would have made things a bit easier, plus it would also be handy for cutting aluminium to size before machining it once the router is up & running.

Yes I though about buy a chop saw. But it would take money away from my CNC budget. I don't mind taking three days to cut a part of aluminium as I can only work for short periods anyway.

Bush Flyer
30-05-2013, 04:18 PM
The next question That I have is about stepper motors and drivers. What is the advantages to having separate drivers for the stepper motors to having all drivers on one board?
I think I will buy the four separate drivers but wanted to check before sending a order.
Now I will buy nema23 motors but what holding torque should I buy 3.1Nm. or will 2.2Nm work just as well, with the RM1605 ball screws I have. Now I know That it would be better "faster" to drive it with belts and pulleys to change the ratio but at this time it will have to be direct drive. I can change it at a later date if I don't like it.
I will be cutting Balsa and ply 98% of the time but I will require the CNC to cut 3mm aluminium and some hard wood now and again.
I have been reading builds on the forum but it seems that most talk about speed but why? I would be happy as long as it does a good accurate job, if it takes a bit longer to cut I don't mind.

Jonathan
30-05-2013, 06:04 PM
I have been reading builds on the forum but it seems that most talk about speed but why? I would be happy as long as it does a good accurate job, if it takes a bit longer to cut I don't mind.

For every material there is an optimal speed (feedrate) at which to cut it and a minimum speed. Optimal is hard to define - it could mean the speed which obtains the best tool life, the highest material removal rate or numerous other factors. The reason we're concerned with maximising the feedrate is if it is too low, you wont be able to cut some materials. Again, weather you can or cannot cut a material with a particular machine is hard to define - for example you could cut aluminium really slowly with a file, but that doesn't really count. For example, since plastics exhibit poor thermal conductivity, they need to be cut with a (relatively) high chipload, to reduce the heat generated by the cutting. Since the spindles we use generally operate best at high speed, this necessitates using a high feedrate to cut plastics otherwise at best the tool life will be poor and at worst it simply wont work. There are ways round this (e.g. using tools with less flutes, use a different lower speed spindl), but in general it's a much better option to choose a drive system which will meet the requirements you expect from these materials.
Even if you don't end up needing the high speed available, the fact the machine is capable of it is advantageous since the machine will be more reliable at lower speeds - e.g you can pretty much guarantee if you've chosen motors/drivers which will move the machine at 10m/min they will never stall or have problems at 5m/min.

In princible there's nothing wrong with having several drivers integrated into one board, so long as they're reliable and suitably rated. The problem is in reality none of them will output enough current/voltage for what you need, so trying to get one to work will not be reliable. Just forget them and please don't post more pictures of TB6560 drivers ;)

You can try Irving's motor calculation spreadsheet (just search that on the forum) to work out which motors would be best. I'd advise using the common 3Nm motors with a 75V power supply. The difference in price between this and other options isn't that great, and it's the best performance you can get without spending a lot more money. I think CNC4You is currently the cheapest place to get the motors and eBay/aliexpress for the drivers.

Bush Flyer
30-05-2013, 07:59 PM
I have just done a member search on ebay but aliexpress have not been trading in the last 12 month
But I will take your advice and order 3.1Nm stepper and four separate drivers.

Ross77
30-05-2013, 10:55 PM
Jonathan has pretty much said it all but just to add that when I first started I said exactly the same thing "don't care if it cuts slow, just want it accurate."

I have since learnt (and stil learning) that cutting slow is counter productive to accuracy and if you take two small a cut then the cutting edge will skate over and work harden the surface making it harder for the following cutting edge to make the next cut, this then causes the tool to deflect and accuracy goes out the window.

It seems odd but there becomes a point when the cutting force increases as the chip thickness decreases. This is because if the radial depth of cut is small it produces a large shear angle so the cutter sees a large area to cut.

Accuracy is more dependant on the correct material removal rate so you need speed and power.


I seems you have to learn how to build a good machine and then learn how to use it:toot:


Jonathan also mentioned aiming for a higher design speed to give headroom on the constant cutting speed but this head room is not wasted as you can have fast rapids when moving between cuts (subject to mass/inertia limitations of course) cut at 5m/min move at 10m/min

martin54
31-05-2013, 06:59 PM
Yes I though about buy a chop saw. But it would take money away from my CNC budget. I don't mind taking three days to cut a part of aluminium as I can only work for short periods anyway.

They are not that expensive & although it would have been another expense which might then mean the overal build took a bit longer it would have been a useful addition for cutting wood & aluminium to size prior to machining in the future. Why take 3 days to cut something when you can do it relatively quickly & then spend the rest of the time doing something else which is more productive.
Have you been to or do you go to your local Pain management centre? If you don't then it might well be something worth looking into. They will be able to help you in all sorts of ways, not with just being able to do a bit of work but pretty much every aspect of life.

Jonathan
31-05-2013, 09:29 PM
I have just done a member search on ebay but aliexpress have not been trading in the last 12 month
But I will take your advice and order 3.1Nm stepper and four separate drivers.

By aliexpress I didn't mean the eBay seller, I was referring to the website:
Cheap CNC! Wantai 4 PCS Stepper Motor Driver DQ860MA 80V 7.8A 256micro CNC Router Mill Cut Engraving Grind Foam Embroidery-in Motor Driver from Industry & Business on Aliexpress.com (http://www.aliexpress.com/item/Cheap-CNC-Wantai-4-PCS-Stepper-Motor-Driver-DQ860MA-80V-7-8A-256micro-CNC-Router-Mill/679049120.html)


Jonathan also mentioned aiming for a higher design speed to give headroom on the constant cutting speed but this head room is not wasted as you can have fast rapids when moving between cuts (subject to mass/inertia limitations of course) cut at 5m/min move at 10m/min

True, but it's worth noting that a high rapid speed (up to a point) doesn't make much difference to the overall job time compared to a lower speed - 5m/min vs 10m/min is a good example. Often you'll find even doubling the rapid speed will only reduce the overall time by a few percent. This is because in general the machine is moving much slower and in many directions with a finite acceleration. The acceleration often limits how fast the machine will go, since every time it moves to a different position, or changes direction, at least one axis has to accelerate (or decelerate) and the speed is often limited by this. One good example is detailed engraving - the individual moves are very short, so each axis is almost constantly accelerating (and decelerating) whilst cutting, and in addition the rapid moves will generally be short so the machine may not get up to the full rapid speed, hence the speed is likely to be limited by the available acceleration.
Similarly, if the G-code is well written then the proportion of rapid moves will be quite small (clearly there are exceptions). Suppose the rapid moves comprise 10% of the total time taken for the job. Here, doubling the rapid speed will only take 5% off the overall job time.

Clearly there are exceptions - if the rapid speed is limiting how fast you can cut, then having more speed (so long as the acceleration is sufficient to use it) will decrease the machining time noticeably. An example of this is surfacing an MDF bed, where cutting at 10m/min would be perfectly reasonable (I do it)...but then how often do you need to surface the bed?

Often it's a compromise between maximising speed and acelleration, since increasing either requires more power and the motors only deliver a finite amount of power. With pulleys you can adjust the ratio to optimise for better speed or acceleration, but in the end you still need motors with enough power - hence my suggestion to get the 3.1Nm motors as their power output is plenty and they're better priced than virtually all other realistic options.

Bush Flyer
03-06-2013, 11:15 AM
Jonathan thanks for the update in finding that site, I have now placed a order for drivers and have also bought the 3.1Nm stepper motors that you advised, That was a good saving in cost. Thanks.

Bush Flyer
13-07-2013, 02:29 PM
Been a while since I did any work to my CNC router as I was in Hospital again for a few days and the wife has band me from the garage. But I did get some wiring done, but have a lot more to do, I'm waiting on a E stop switch and more wire.
So just some photo's where I stand at this time. I hope to get going again in the next couple of weeks.

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Bush Flyer
12-08-2013, 01:23 PM
I am managing to get back to the garage for a hour here and there still real sore. I have finished the control box for my cnc but I still have some wiring to Finnish on the limit switches.
I also got some more of the cnc assembled, the next job is to build a table that will house the computer the controller and the cnc router all in one. Then fit a new wall plug in the garage and a bracket to the wall for the monitor.
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GEOFFREY
12-08-2013, 08:21 PM
Love the model aircraft. Router looks good too. G.

irgonomics
12-08-2013, 10:42 PM
Looks like you are nearly ready to start cutting. Just got a couple of concerns with the power supply. Firstly I can't see in the photos how you are going to cut the power with the e-stop. Also you may have problems with noise bundling all of your signal and power cables together. Anyway, looking really good.

Regards, Ian.

JAZZCNC
13-08-2013, 10:07 PM
Also you may have problems with noise bundling all of your signal and power cables together.

Ian's correct here.! . . The worst thing you can do is use un-sheilded cable and tie signal and power cables together like you have here.!!

Things may appear to work ok just jogging around etc but the potential for problems increases big time while cutting with noise getting on the signal wires causing all sorts of strange things to happen.? . . . .Everything from sudden limit or E-stops trips to sending phantom signals to motors causing them to either go in wrong direction or increase steps etc.
Honestly Complete nightmare tracking down where it's coming from so anything to minimise the better and you've done everything to maximise with those cable ties and unsheilded cable on signal wires.!

Other than that looks Good and happy cutting.!

Bush Flyer
18-08-2013, 12:23 AM
There was nothing in the instructions from cnc4you about shielding, I now need help, do you shield just the wires to the stepper motor, or do you shield the stepper motor wires from the limit switch wiring.
What a mess there is over 70 of wiring there including the plugs.
And here was me thing I was smart keeping all the wiring neat and tidy, Now how do I fix this. Do I let the wires loose is this good enough just leave them loose in a cable track or can you get screening to fit around the cable on the out side of the insulation on the power wiring and of course you need to earth shielding do you earth the shield at one end or both.( On google search I found some mesh but was 30 for 5 metres and you get Tin-Plated Copper Foil Shielding Tape from 3M its about the same price what would you use or is there something better?) Will I have to rewire the inside of the control box or is it just the wiring to the stepper motors and the limit switch's?
On another search I found Guitar Pickup copper foil tape would this work and do I shield each of the four wires from the stepper motor separate?

Swarfing
18-08-2013, 12:27 AM
For the cost of that Mesh you could buy some CY cable and be done with the problem?

JAZZCNC
18-08-2013, 12:43 AM
Ok well first before you start ripping it apart just do some better cable management.

Separate the signal wires from the Power wires and run power cables together.
Don't cable tie the signal wires together just run along side each other lose.

Shielded cable is the proper way and should really be used and like Swarf says just buy CY cable if you do.
You'll find it here cheap enough and just use 4 core 0.5mm or 0.75mm. CY Cable (http://www.csecables.com/acatalog/CY-Cable.html)
Only ground one end at the control box and make sure your control box uses star grounding. IE all grounds to same spot.

But it doesn't always follow that because you haven't used shielded cable you'll have problems it could work fine but you are much more open to interference and corruption of data signals without it. . . . I suggest you try machine and if any strange happenings like Z axis lifting/dropping or false limit or E-stop signals then you'll be getting noise on the lines.

Regards which wires to sheild then it's motors and limit cables, any cables that send signals. Following on from above, if you have trouble with noise then chances are it will be the limit cables that cause it because they tend to be the longest run, effectively acting has a big antenna sending and receiving signals. Similar applies to the Stepper cables because they are long.

Main thing is to keep power cables away from signal cables and shield any signal cables. This esp applies to spindle cables if your using a VFD which are very noisy things.

Swarfing
18-08-2013, 01:02 AM
Shielded cable is the proper way and should really be used and like Swarf says just buy CY cable if you do.
You'll find it here cheap enough and just use 4 core 0.5mm or 0.75mm. CY Cable
Only ground the ends at the control box and make sure your control box uses star grounding. IE all grounds to same spot.

Note he just means one end of the cable and not both. On the other hand you may get away with it and it all work fine? i did on my first one and that was a can a of worms. Saying that set it up right first time and you will have less problems to sort out later (spending hours guessing what the problem is).

Bloody nice job by the way and a credit to the build so far. You have worked very hard ;-)

JAZZCNC
18-08-2013, 01:13 AM
Note he just means one end of the cable and not both.

Ye I did and corrected it now has wasn't clear was it. .


Bloody nice job by the way and a credit to the build so far. You have worked very hard ;-)

Ye and I'll second that has well.!!

Bush Flyer
18-08-2013, 10:40 AM
Thanks for the help, I have had a look at that CY Cable, I wish I had found that before I had started the wiring, Never mind I will separate the wiring to see if I get away with it . But first I will have to make new bench for the machine then I will be able to try it too to see how it works, But in the end I will slowly change the wiring to this CY Cable starting with the limit switches.
My thanks again Mike.

Bush Flyer
26-09-2013, 10:06 AM
Well it's been a while since I posted a update. I have done some cable management and separating the wiring, Also I have made a table for the CNC to be bolted down on and also store the controller and computer underneath the CNC Router. I Bought a new monitor and mounted it on the wall above the CNC. I loaded in Mach 3 and now there life. I Quickly made up a spring pen holder and it drew it's first picture I am so chuffed. I got the computer from a friend that he had windows XP on it that had never been used since 2005. I was going to use the same computer to run the Mach 3 program and the CAM program, but find it's not practical. I will have to build another computer to run the Cam program like Artcam express as my laptop crashes when trying to run Artcam express and I also tried Vectric cut2D but the Graphics card in the laptop could not handle the program. It's some thing that I did not budget for. I have a case and some other parts already so it should not be to bad. All that I am waiting for now is some cable tracking from china and some single and double flute bits and I can try some cutting. There is some parts I will improve like replacing the wiring but for now it's running.
My original budget that I worked out was for 1200 so I said it would cost a Total of 1500 when finished But I made some changes as I was building it so now the cost when finished including a second computer will be nearer the 2250 mark, it's so easy to get carried away, I built this to so that it would cut parts for my RC models but I have already started think about building a laser CNC, this has turned out to be another hobby on it's own.:adoration:

Bush Flyer
20-11-2013, 04:04 PM
Well I now have Artcam express and Mach3 licence bought and its seems to be running well, The only concern is the stepper motors get hot after it has been running for 45 to 50 minutes is this normal the axis all run free so there is no binding in the bearings etc.

Jonathan
20-11-2013, 04:05 PM
The only concern is the stepper motors get hot after it has been running for 45 to 50 minutes is this normal

Motor case temperature up to 80C is considered acceptable.

Bush Flyer
20-11-2013, 09:19 PM
That's Fine its below that I measured the two X axis motors at 71 degrees the Y axis was 68 degrees and the Z was not worth measuring, so all good will just test again after I have a long cutting job to do.
Thanks Mike.