BUILD LOG: Steel frame cnc router design/build [Archive]

CraftyGeek

06-08-2013, 02:16 PM

It may be a little premature to start a build log - but I think it makes more sense to be asking questions regarding my design/build in a single thread rather than scattering questions across the forum.

I built an MDF CNC router a few years back using a design modified from the original buildyourcnc.com plans. We moved house a couple of years ago - the machine has sat unloved in (warped) pieces in the garage since.

I was planning on building a modified FLA-100 using aluminium profile - but i've already been talked out of that approach (see this thread (http://www.mycncuk.com/forums/diy-cnc-machine-building/6373-diy-linear-bearings.html)).
I'm now instead designing a machine from scratch using 50 x 50 x 3 steel box bolted together. I'm aiming for a cutting area of 1200mm x 600mm. The machine will mainly cut MDF & wood - but plastics & aluminium are also a distinct possibility.

I have all the electronics from the previous build which include:
3x Nema 23 motors
all control boards, breakout board, 24v power supply (to be upgraded in the future) & dedicated PC at the ready.
Spindle will just be a trend router for now - another part to upgrade later.

I now plan on using supported rails from Chai/ebay.
Leadscrews are, as yet undecided.

I'd like to use 2 X-axis leadscrews - but the financial side of things may keep this as a single leadscrew for the initial build...then move to 2 as an upgrade later.

I've started drawing up a design which is far from complete. The board on the curtting surface is sized at 1200mm x 600mm for use as a guide only. In practise the lower shelf surface & full table would be covered with MDF. There's no diagonal bracing anywhere either..that can be added in later.

At the moment i'd like some feedback on the general approach & layout. I have a few minor concerns at the moment one being am I over engineering it?

I've also started wondering about bolting the frame together - there's a lot of holes to drill/tap & bolts to buy which will be time consuming & more expense....which leads to me to wonder whether its worth buying a cheap arc welding starter package (£60-75) & weld the frame instead?

Be gentle with me ;-)

JAZZCNC

06-08-2013, 02:31 PM

I've also started wondering about bolting the frame together - there's a lot of holes to drill/tap & bolts to buy which will be time consuming & more expense....which leads to me to wonder whether its worth buying a cheap arc welding starter package (£60-75) & weld the frame instead?

Bit busy at minute to reply properly to machine but I will later.!! . . . .This is just a BIG Yes to welder, it's not has difficult has you may think. Buy good rods and keep them dry, warm them in oven before using makes striking up much easier which is were most first time welders struggle.

You won't or don't want to be doing long continuous runs of weld just short runs and spread around to keep heat from distorting metal. Less than 1hrs practice on some scrap and you'll have it sussed good enough to do what you want.!!

CraftyGeek

06-08-2013, 02:55 PM

i thought you might say that...is a cheap Arc welder up to the job in hand though? Anything I need to be aware of? (sorry I have absolutely zero knowledge of welding)

I'll need to rework the machine assembly to allow for welding rather than bolt together...it'll be cleaner layout.

kingcreaky

06-08-2013, 07:28 PM

yeah, get a cheap machine, it will be fine

beauty of arc welding, is its EASY especially if your welding 2mm+ mild steel. even easier with new steel

get 6013 rods. say about 3.2mm (which again are good allrounders)

CraftyGeek

06-08-2013, 08:08 PM

Thanks kingcreaky - i've spotted a Ferm 100A unit on ebay that comes with basic accessories that looks like it should be enough to get me started.
Regarding the rods - what does the 6013 bit mean?

I've done a quick reworking on the design so far for welded assembly - it currently has a bottom on the gantry for a single leadscrew, not sure if this is staying yet or not (probably not).
As mentioned before, i'm interested in comments about the approach as a whole - not anything too specific yet as i've still got quite a bit to do on it.

kingcreaky

06-08-2013, 08:33 PM

a 6013 is just a type of welding rod. Reading into it before posting this it appears 6013 seems about the most common type used but here is the speal if your interested

Different Types of AC Welding Rods | eHow (http://www.ehow.com/list_7161839_different-types-ac-welding-rods.html)

no doubt this clever lot on here will tell you these are the wrong ones... but they are the ones ive always used. Work perfectly fine all weather for me

regarding your design...

Good start... ive seen a lot worse.. but in my opinion...

*id have a center leg on each side rather than use the bed horizontal as brace (you could use that aswell)
*more bed frame crossmembers
*forget the single ballscrew arrangement for the X, use two one on either side
*triangulate the corners wherever possible
*If you think its over-engineered at any point... its not.. you watch it dance round the workshop like its made out of carboard when its cutting. You wont regret stregth in design

read ALL the other build logs...

My machine

http://www.mycncuk.com/forums/router-build-logs/5174-operation-cnc.html

is similar to your design

JAZZCNC

06-08-2013, 10:39 PM

Thanks kingcreaky - i've spotted a Ferm 100A unit on ebay that comes with basic accessories that looks like it should be enough to get me started.

No Don't buy 100A welder you need more Amp's spare for duty cycle. Biggest problem with cheap Arc welders is low Duty cycle or better put the time you can weld before the it trips out from over heating is short.!!
Now your not going to be running long welds or in a rush so it wouldn't probably be a major problem but for £10-20 more you could get 140-160A and have decent duty cycle with less stress on welder.

Like Matt says 6013 rods but more important is ONLY buy decent quality IE: branded name BOC, MUREX etc none of this rubbish you see at Aldi or car boot sale etc and keep very dry.

Regards 6013 it's the AWS standard (American Welding society). Rods usually have prefix like E-6013 and it breaks down like this.!!
E= Suitable for MMA welding and flux coated
60= Minimum tensile strength in KSI(Kilo-pounds(force) square inch) IE 60Ksi = 60,000psi pounds(force) per square inch.
1= Suitability for welding positions . . . IE: 1= All positions 2= flat & horizontal positions
3= Flux coating type and suitable Current types IE: 3= High titania potassium (Rutile) AC or DC+ current.

See here for a good Arc tutorial and loads of info.
Arc Welding Tutorial (http://www.mig-welding.co.uk/arc-tutorial.htm)

I'll look at frame and come back to ya.!!. . . . Get ya hard hat on ready. . .Lol

JAZZCNC

07-08-2013, 02:52 PM

Ok I'm back with my wrecking ball . . Get ready.!!. . :hysterical:

So I see you've been paying attention with using the high sides and gantry sat on rails design which is great for twin screw machines but in this case it's actually hurting your design badly.?

Because your wanting to use single screw (with option to upgrade) this means having gantry cross brace but with those high sides it means having long gantry sides which are acting has levers. They will flex, twist and stress the bearings, they will also resonate like crazy, this all transfers back to the work or like Matt hinted at make the bloody thing dance around the room if bad.!!. . . Not good design for this way of doing it.!

Really because of your budget restrictions then your going to have accept a bit of compromise on design.? In this case it's flexibility regards cutting height and materials you'll be able to cut. The high sides with gantry on rail design works very well if you want strong rigidity and flexibility of lifting the bed but it just don't work for use with single screw.

So your going to need a way to keep Gantry sides short has possible but yet high enough to give clearance you'll need for cutting what you want to cut.? . . . . It's simple enough you can't have high clearance and high strength,it's always a compromise with this way of doing it.
So best thing is first decide the lowest clearance you can work with a build frame that allows gantry to be kept short and strong.!

There's several ways to build frame to allow this and I'm not going to try telling them all I'm just going to show the sort of thing I'd build for this Budget and upgrade has you can afford way of doing things. (It's just something I knocked up to show principle not finished design)

This gantry/frame design will be very strong and use's roughly 2.5 x 7.5mtr lengths of 80x40x3. It can easily be converted to twin ballscrews.
It's shown has desktop machine to keep cost's down but making it free standing would be simple enough just cost more.

Hope this helps and carry on it's perfectly do-able to build strong machine even on budget.

Oh one more thing or Tip with modelling.? . . Get accurate dimensions or better still Cad models for the things you plan to use, like ballscrews, motors etc has it's easy to think I'll use this or that like this and then it doesn't fit or interferers with something else.

CraftyGeek

07-08-2013, 04:03 PM

Thanks Jazz.
I have made a few changes since I posted that last image...the main one being the removal of the single leadscrew option. I've decided that I want to do a decent job of this, which means it'll take me longer to get it running - but the end result will be worth it...so dual leadscrews from the start - hopefully driven from a single motor.

I'm still very much tinkering with the overall dimensions - I have shrunk the z depth & reduced the overall height a bit as well.
I hope to have a bit more time to spend on it tomorrow to make some more changes, then i'll come back for another slap on the back of the head :-)

On the gantry you posted above - I assume that the spindle mounts between the *ahem* open legs?
Question...does the distance fore/aft that the spindle is mounted (relating to the x rail bearings) have any effect other than allowing the cutter to reach different areas of the table?

JoeHarris

07-08-2013, 08:43 PM

CraftyGeek

07-08-2013, 08:56 PM

I can recommend the Clarke Easi arc welders from machine mart... Mine has been great so far. Also just got an evolution rage 2 cut off saw for slicing up all the steel - again it's awesome but chucks little bits of swarf everywhere! Good luck with it - you're in good hands with Jazz he tells it how it is!!

I'm currently eyeing up a Ferm 160Amp job at the moment - looks like it should do the job nicely.

I got an Evolution Rage 3 last year...love it - it won't stop for anything!
Despite hooking it up to a decent dust/chip extractor it still chucks out crud everywhere :-p

JAZZCNC

07-08-2013, 09:28 PM

On the gantry you posted above - I assume that the spindle mounts between the *ahem* open legs?

Yes just slapped some bearing and front Z plate on to show see pic.

Question...does the distance fore/aft that the spindle is mounted (relating to the x rail bearings) have any effect other than allowing the cutter to reach different areas of the table?

Some would throw math's and moments of inertia etc shit like that at ya but in reality it's nothing to worry about really, so long has your not daft about it.
I just try to keep the overall weight balanced on the X bearings. Mostly It's just balancing act between losing or gaining cutting area.

CraftyGeek

08-08-2013, 09:02 AM

See here for a good Arc tutorial and loads of info.
Arc Welding Tutorial (http://www.mig-welding.co.uk/arc-tutorial.htm)l

Had time to have a quick look at that page this morning - that's a fantastic resource, Thanks!

CraftyGeek

10-08-2013, 07:26 AM

I'm looking for more local sources for materials. I have a good local steel yard 5 miles up the road that i've used several times before - so am happy to use them for the framework, but their aluminium stock is low, a bit battered & unreliable.

I've found that there's a branch of Blackburns Metals not too far from where I work - does anyone have any experience with them as a supplier for aluminium?...quality & prices ok?

JAZZCNC

10-08-2013, 10:08 AM

No experience with Blackburns but if you haven't got a milling machine to surface standard plate then who ever you use I recommend you buy ground flat plate for key areas like Z axis and bearing plates. . . . It's more money but worth the expense because standard plate is never flat, it may look flat but it's not.!! So for critical areas like Z axis and bearing plates where surfaces must be flat and parallel to each other they must be surfaced flat.
I have the capability to surface plate and still I buy ground plate for these areas has it saves me hassle and time and even careful milling can't match ground surface quality.

Even Round rail which is very tolerant of bearing/rail miss alignment will bind and stick if plate is slightly cupped, less than 1mm cup, bow or twist over 300mm bearing plate length will be enough to totally lock the bearings when fastened to plate. Normal rolled plate can have that much error and I've seen plenty folks fall foul of this and corrected several bearing plates for people because of this.

If you can't get it from Blackburns then I suggest aluminium ware house because they cut to size and you can order just slightly larger than you need for those areas. Your Looking for ECOCAST at AW it's here. Aluminium Plate - Cut to Order - Aluminium Supplier | Aluminium Stock | Aluminium Warehouse (http://www.aluminiumwarehouse.co.uk/cutting_calc.php)

PS: For rest of plates like motor mounts and even gantry sides etc then normal plate is fine, if you have decent metal scrap yard near by it's worth checking them out has often they have offcuts etc from industry and some can be large and quality, most just charge scrap value.

CraftyGeek

10-08-2013, 10:46 AM

Thanks Dean,

At the moment I was thinking more for the less important parts - motor mounts etc as it will make life a lot easier having a reliable local source that I can nip into to get the occasional piece without any postage costs.

I've seen AW mentioned in several build logs & have them bookmarked already when it comes to the important parts. It seems the narrowest width for the Ecocast is 100mm which may well make a design decision or 2 for me as well...although this could be an issue when it comes to mounting the Y rails on top/bottom of the gantry?

I assume that 5mm Ecocast will be ok for the rails to mount to?

Robin Hewitt

10-08-2013, 10:57 AM

CraftyGeek

10-08-2013, 11:41 AM

If however you plan ahead and weld plates bearing bolt holes to your bars you have a chance to straighten things up after everything has cooled down.

Hi Robin - could you elaborate on this bit a little...I'm not fully sure what you mean.

I'll be taking it slowly, small tacks to pin it together first - check it all, then go round again.

Robin Hewitt

10-08-2013, 11:48 AM

Easy to find out for yourself. Saw a piece of box section in half, weld it back together, see how straight it is.

JAZZCNC

10-08-2013, 12:02 PM

I think steel is an excellent idea, so is a stick welder, but I would still like to take this opportunity to screw up your whole design at the last moment because that is what I do best :pride:
.
When a weld cools it solidifies then shrinks. The shrinking bends everything out of shape with no possibility of correcting it. If you are a novice welder your welds are unlikely to be drop dead gorgeous and the effect is amplified.
.
Meaning you end up with a framework that is wildly out of square, it fills half the workshop, is tricky to get it out the door and take it up the dump.
.
If you are fiendishly clever you can try to pull everything square by welding in cross braces after the event and hold the thing in tension.
.
If however you plan ahead and weld plates bearing bolt holes to your bars you have a chance to straighten things up after everything has cooled down. A round file can move a bolt hole, an angle grinder can square up a face, packing can be tack welded in place.

Don't listen to him he's just like to blow the froth of peoples coffee . . .:hysterical:

He's partly correct about heat and cooling, shrinking but if done correctly like I said short welds spread around it can be minimised enough to be fine. The wildly out of square comment just means he's been doing it wrong. .:whistle:

The squareness of the frame isn't critical, yes it's got to be close but 1-3mm or so out won't hurt.! And if welded has mentioned it won't warp or twist anywhere near that amount.

It's the rails that matter and these MUST be square and parallel to each other and on the same plane.
To help your self with this on the Long axis, which I call X it pays not to weld the top rail but bolt it to flat plates. If there's any error then you can shim into plane and move parallel and square to each other very easily.

Then there are other little tricks for dealing with things like the top plates rails sit on arn't flat etc. Putting Epoxy putty between rail and plate creates a lovely surface and give enough time shim square etc and then when dry you have perfect surface and it's also helps dampen resonance.!!. . . . There I've give one of my tricks away. . Dam.:distress:

I do this all the time so believe me it's not difficult so don't let comments like "Victor" Robin "Meldrew" put you off welding because it's by far the Cheapest and strongest way to build a machine.

Edit: Better elaborate on the Epoxy comment.!! . . . You must put piece of cling film or thin plastic between top rail and putty other wise you'll stick the buggers together and never get them off. .:stupid: . . . .Oh and it's not expensive. 125g packs for £2 and it goes fair way has your only spreading thin, 2-3 tubes will do full machine.

CraftyGeek

10-08-2013, 12:04 PM

I understand that bit - its the 'weld plates bearing bolt holes to your bars you have a chance to straighten things up' bit that i'm not clear on the meaning of...

CraftyGeek

10-08-2013, 12:09 PM

To help your self with this on the Long axis, which I call X it pays not to weld the top rail but bolt it to flat plates. If there's any error then you can shim into plane and move parallel and square to each other very easily.

Like that....pinched ;-)

JAZZCNC

10-08-2013, 12:29 PM

Anyway back on track.!!

I assume that 5mm Ecocast will be ok for the rails to mount to?

Because using supported round rail then I wouldn't bother with Ecocast has the rail base will have more error than the steel. You only really needed plates between when fastening to Ali extrusion. If that's your plane then just buy normal Ali about 10mm.

If your meaning 5mm plate to sit on bearings then NO you'll need absolute minimum 10mm, 15-20mm is the norm.

r0bsk1

10-08-2013, 02:18 PM

JAZZCNC

10-08-2013, 03:16 PM

Try sellotape or brown packing take next time. It self releases.

Yep good idea, I just normally use plastic sheet because I generate shit loads of it at work and it's free. .:applouse: . . .. Well not free suppose because I've paid for it when bought the bloody stuff it was covering. .:highly_amused:

CraftyGeek

10-08-2013, 07:15 PM

Edit: Better elaborate on the Epoxy comment.!! . . . You must put piece of cling film or thin plastic between top rail and putty other wise you'll stick the buggers together and never get them off. .:stupid: . . . .Oh and it's not expensive. 125g packs for £2 and it goes fair way has your only spreading thin, 2-3 tubes will do full machine.

Is this a thick fast cure resin, medium/slow cure with additive/filler or some sort of putty that i've not come across before?

In other news - i've ordered a 160A Arc welder via an auction on ebay...will need to pay a visit to my steel yard shortly to get some scrap to practice on.
The steel yard also sells welding rod - i'm assuming that because they do fabrication themselves they'll be decent rods...they do a box of ~250 6013 3.2mm for about £28+VAT - does that sound ok?

JoeHarris

10-08-2013, 08:05 PM

I recommend this archaic video if you are learning to stick weld...
www.youtube.com/watch?v=zWdgEaXWDxQ

Robin Hewitt

10-08-2013, 10:08 PM

The wildly out of square comment just means he's been doing it wrong. .:whistle:

Jazz will now tell us how far out of square is acceptable and I will stand by to say "Told ya so!" when it all goes tits up :victorious:

You will require an angle grinder.

CraftyGeek

11-08-2013, 06:01 AM

You will require an angle grinder.

I've already got one with a supply of thick & thin discs ;-)

joneb

11-08-2013, 08:32 AM

You may be interested in my steel frame router Home Built GantryMill Improvements - YouTube (http://youtu.be/mWVltr98MOM) the cutting area is 600mm x axis and 350mm y and 100mm z. It is built with materials I had to hand hence the mixture of steel and aluminum.

I would like to echo Robins comments about distortion caused by welding, it can be a nightmare so you will need to be very careful, also it is easier to weld thicker material but harder to remove the distortion.

Home (http://www.john-bannister.co.uk)

CraftyGeek

11-08-2013, 03:40 PM

I recommend this archaic video if you are learning to stick weld...
MMA welding (welding institute) video guide - YouTube (http://www.youtube.com/watch?v=zWdgEaXWDxQ)

That's a great video - just watched it all the way through...i'll probably watch it again before having a go myself.

JoeHarris

11-08-2013, 05:57 PM

Only trouble is how easy "max" makes it look to get a perfect weld!! I was more than a little disappointed with my first couple of attempts!

JAZZCNC

11-08-2013, 09:38 PM

Jazz will now tell us how far out of square is acceptable and I will stand by to say "Told ya so!" when it all goes tits up :victorious:

If you look again you'll see I mention 1-3mm.!!. . . Now let me ask you this Robin.! . . How many Steel framed routers have you built.?

I'll say it again just to be clear.!!. . So long has the welds are kept Short 1"-2" Max and Don't weld in one spot moving around the frame you'll be fine. Even just welding several short bursts and having a break to prevent heat form travelling if your unsure will help. . . . Remember it's DIY so there's no Rush it doesn't have to be done in same day.!

Is this a thick fast cure resin, medium/slow cure with additive/filler or some sort of putty that i've not come across before?

It's a 2 part putty paste called Milliput, see here Milliput - The epoxy putty with a thousand uses in modelling, DIY and industry (http://www.milliput.com/)
Comes in sausage shaped cellophane wrappers. Easy to use just mix equal parts in your fingers just like mixing Play-doh. Then spread on Clean dry surface and sets like concrete in about 6-8hrs, packet says 3-4 but I've found it's longer and leave over night. Leaves a super flat surface it can be tapped, filled and ground just like steel.

Here's Where and how I use it. It's also why steel or frame distorting slightly is no big deal.!!

Most of the frames I build are a mix of welded and bolted like these pics below. ( Frame only here no Bed, it's adjustable) At the joints and where top rail sits on plates is where it's used.
When I'm all finished and welding up then I bolt frame together to get an idea of how far off things are.? Most the time they are hardly off at all and just a quick grind or tweak of mounting plates brings it near enough to call Ok.!! . . . Some times shims may be needed.
Remember the rails being parallel and on same plane are the important areas and because the top rail is Bolted we have complete control and adjustment of this. It also doesn't get welded so NO distortion happens, just choose the straightest unbent piece you can find. (We have ways around bent rails has well but won't get into that now.)

Now in most cases after shimming or grinding true and square I could leave it at this but I don't. I go one further and disassemble again this time rebuilding with Epoxy putty at each joint with cellophane between to prevent sticking together.
This gives me about 1hr to set the frame square and true, Doesn't matter if the welded frame isn't quite square or plates not perfectly flat etc because the putty is going to take up any slack. . . . . So long has the shims from first assemble are used then All that matters is that frame is SET square and uprights vertical Now because Putty's going to fill any discrepancy and when it's set solid over night you have perfectly flat and true surfaces. The shims can be removed or set left into Epoxy.
Now where not talking 5 -10mm thick epoxy pads here, there often just wafer thin just filling voids etc.
Drilling and pinning the joints with dowel pins helps make sure everything goes back in same place and makes assembly easier.

Again the main frame being 100% perfectly square isn't overly important, it's the top rails that matter.!! . . Can't stress this enough.

Now what can be more of a pain to deal with is Twist of welded sections from distortion but again depending on design etc this can be got round. Often it's just a case of forcing the twist out by twisting in opposite direction, if twist is happening then you can often see it has your welding so stop and twist it back. This is also why spreading the welds around is important.
The bed is the main area you need to keep an eye on distortion and even then again Epoxy can be your friend if really bad and with a bit of Brute force and epoxy if need be then the Bed can easily be sorted to within a knats cock. When spoil board is surfaced then it will be Cock On.!!

Now here's what the scare mongers, who probably have never built a steel framed machine are not saying.? . . . If at first you don't succeed just grind the bastard apart and re-weld or re-set that's one of the beauty's of steel is it's flexibility for having another crack at it.

Robin Hewitt

12-08-2013, 09:20 AM

Now let me ask you this Robin.! . . How many Steel framed routers have you built.?

Like this? None. Every router I have made has been job specific :topsy_turvy:

CraftyGeek

13-08-2013, 02:33 PM

Ok - design progress time.

I've been focusing on the frame/table so far - its now at a stage where i'm pretty happy with it & I think i've added everything that I meant to.

red = 60x60x4 box
blue = 50x50x3 box
green = 60x4 flat bar
orange = 50x4 flat bar

Rails are sat on 50x10 ally flat.

Ignore the floating guide leadscrew for now - its just there as a vague reference as to where i'm planning to put the leadscrews at the moment. Also ignore the holes going through the outside of the legs, they won't be there when I make it.

The frame has the ability to be adjusted for square in every direction. The cutting surface can be positioned in 5cm increments down the legs.
Both the lower surface & cutting surface will be covered in mdf added further bracing.

Hopefully this will mostly get nods of approval :uncomfortableness: so i can move on & start thinking about leadscrews, motor mounting & the gantry in more detail.

JAZZCNC

13-08-2013, 04:47 PM

Ok looking much better.!! . . . Take it you have decided not to weld.? If so Not saying this is bad thing if that's what your most comfortable with but will be a lot more work and maintenance. Mixture of both works best IME.

Only thing I see and question is DO YOU really need that much adjustabilty of the bed.? If not then I'd raise the lower frame and increase the triangulation. Will just help stiffen the frame a little.

Crack on.!!

CraftyGeek

13-08-2013, 05:13 PM

There are still welds in there - I think I need to see how I get on with the welding to see how accurate I am with it...then if I feel confident enough, i'll drop more of the bolts & weld instead (like the table surface). I do want to make it so that the whole frame can come apart into manageable sections for moving house etc in the future.

Regarding the height adjustment - I don't know is the short answer...I've seen that others do it & it might be useful for me at some stage - but I don't have any examples in mind. In reality I probably don't need that much. I'm also still playing with the overall dimensions a little - so i'll still be tweaking for a while.
The frame at the moment should be a decent height for me to work at - i'm conscious of making it too low & giving myself back issues (which I get from time to time)...more cross bracing can be added at a later date easily enough.

JoeHarris

13-08-2013, 06:40 PM

[QUOTE
Most of the frames I build are a mix of welded and bolted like these pics below. ( Frame only here no Bed, it's adjustable) [/QUOTE]

Jazz, do you mind explaining how the bed adjustment holes work on the frame pictured. It looks like you have another tapped plate or something inside the RHS? Cheers
joe

JAZZCNC

13-08-2013, 07:08 PM

Jazz, do you mind explaining how the bed adjustment holes work on the frame pictured. It looks like you have another tapped plate or something inside the RHS? Cheers
joe

Yes there's a 10mm thick plate with holes tapped it.The holes in legs are drilled oversize for clearance. The 10mm plate is tacked in place to hold.

The main bed frame is heavy so there's 4 lead screws (2 each side) to help lift up and down and roughly get into position. Then there's 8 angle plates(4 each side) fastened to bed frame with 2 holes in each so 16 Bolts total that bolt into uprights with 10mm tapped plates inside.
It's simple and easy thou to be honest it's not something you do very often has usually you'll settle on a position that allows 90% of what you want to do.!. . . . It's just nice having the flexibility to do oversize things when needed.

CraftyGeek

15-08-2013, 08:20 PM

Chaps - i'm dithering about with the gantry quite a bit...can't come up with an approach that i'm happy with yet.

I've been looking around at a lot of build threads on here & cnczone...I haven't seen a gantry design that seems to suit what i'm doing.

Firstly - do I need to be concerned about weight. ie, am I ok using steel box or is this something that I may regret later?

Secondly - Jazz, the mock up design that you posted earlier in this thread - the gantry on that has 2 lengths of steel box attaching to vertical end pieces. I assume this would have to be a weld - my concern here is alignment & the lack of adjustment. Is there another way of going about it?

I'm trying to keep the range of materials that need to be purchased down...i've been looking at using aluminium box with a vertical plate - but it starts upping the budget quite quickly.

I'll also drop in a note here that I also really like the simplicity of KingCreaky's gantry...cheaper than some options, but the ally rect box & front plate add up quite quickly.

Any thoughts?

kingcreaky

15-08-2013, 08:58 PM

Chaps - i'm dithering about with the gantry quite a bit...can't come up with an approach that i'm happy with yet.

chaps, im going to stick my neck out here, and before I even say anything Ive only made one machine... but what I do have in common with CraftyGeek is I am also DIY, so this was my gantry approach, slate it if you will, its not perfect but it was all done by hand with pillar drill hand punch and ruler.

949794989499950095019502

JAZZCNC

16-08-2013, 12:02 AM

Firstly - do I need to be concerned about weight. ie, am I ok using steel box or is this something that I may regret later?

No but within reason, weight is your friend when cutting has it allows deeper depths of cut, obviously there's a limit and it affects other areas of machine like motors, drives, screws etc if you go too heavy. Stay within 80Kg and you'll be ok with steppers.!!. . . Heavier than this and you'll be into servo territory.

Secondly - Jazz, the mock up design that you posted earlier in this thread - the gantry on that has 2 lengths of steel box attaching to vertical end pieces. I assume this would have to be a weld - my concern here is alignment & the lack of adjustment. Is there another way of going about it?

Doesn't really matter because all the adjustment is taken care of thru the rail mounting and were gantry sits on X axis bearings. . . The only requirement is that it's not twisted.

There are several ways to do different and I just drew this quickly to give an idea of easy and strong which go with single screw.
Really how you go about it depends on the job in hand, like in creakys case it was simple but would only really be suitable or woodwork type cutting any harder material like aluminium or if higher accuracy say for fine engraving, by that I mean in brass or Aluminium, PCB's etc where required then this is when weaknesses show thru quickly. . . . Resonance and vibration being the enemy has hollow aluminium box isn't stiff enough.! . . . It's also only works with twin screws and with single screw wouldn't be very good at all.!!

Your problem or complexity/weakness comes from using single screw.!!

JoeHarris

16-08-2013, 12:08 AM

Yes there's a 10mm thick plate with holes tapped it.The holes in legs are drilled oversize for clearance. The 10mm plate is tacked in place to hold.

The main bed frame is heavy so there's 4 lead screws (2 each side) to help lift up and down and roughly get into position. Then there's 8 angle plates(4 each side) fastened to bed frame with 2 holes in each so 16 Bolts total that bolt into uprights with 10mm tapped plates inside.
It's simple and easy thou to be honest it's not something you do very often has usually you'll settle on a position that allows 90% of what you want to do.!. . . . It's just nice having the flexibility to do oversize things when needed.

Cheers. What thread are those then? I think I read somewhere that you favour m5 due to number of threads but they look bigger? What do you tend to use for plated connections?

[reason I ask is my 4.2mm bit is knakered and I'm looking at replacing it with a taper bit as my chuck is not the best... If m5 is not the way to go I may not bother just now..

Joe

JoeHarris

16-08-2013, 12:14 AM

Your problem or complexity/weakness comes from using single screw.!!

Get onto old Chai he'll sort you out with an extra screw for a bargain price and you won't look back!

JAZZCNC

16-08-2013, 01:26 AM

Cheers. What thread are those then? I think I read somewhere that you favour m5 due to number of threads but they look bigger? What do you tend to use for plated connections?

[reason I ask is my 4.2mm bit is knakered and I'm looking at replacing it with a taper bit as my chuck is not the best... If m5 is not the way to go I may not bother just now..

Joe

They are M10 Joe. I only use M5 for linear rails where they tap direct to steel box. Most other stuff like Z axis then M6 or M8 depending on plate size.

Wouldn't use a taper drill for threads there not accurate enough really, Ok for general holes.

CraftyGeek

16-08-2013, 06:12 AM

On the x-axis I am going to use 2 leadscrews with a single motor.

Ok - i'll draw up a revamped steel gantry...I have a slightly revised approach in mind now...i'll be back with a design for you to tut at later :-p

JoeHarris

16-08-2013, 07:04 AM

They are M10 Joe. I only use M5 for linear rails where they tap direct to steel box. Most other stuff like Z axis then M6 or M8 depending on plate size.

Wouldn't use a taper drill for threads there not accurate enough really, Ok for general holes.

Thanks Jazz, What about where you are joining the various sections of the steel frame together? I am going to be tapping directly into 3mm wall steel for most of my connections...

CraftyGeek

16-08-2013, 10:31 AM

Ok - I have a gantry drawn up now that i'm feeling much happier about.

Weight as it stands currently is approx 28.5kg...obviously z-axis & spindle etc still need to go on.

Motor mount shown is rough & a guide only.
Leadscrew is guide only.

Teal parts: 75 x 50 x 3 steel box
Green parts: 60 x 5 steel flat bar
Bearing mounts: 15mm ecocast
Front vertical plate: 5mm aluminium plate
End braces: 15mm aluminium plate
Rails are mounted on 50 x 10 aluminium flat bar

Hopefully this is a decent blend of strength, precision/alignment & weight.:concern:

Bracing for impact...thoughts?

jcb121

16-08-2013, 02:13 PM

here's another idea for the ganrty, a bit more expensive solution though as the sides need to be machined/watercut.

9513
9514
9515

so 20mm alu plate reinforced with solid 25mm square bar. 20mm plate all around.

to attach the ballscrew nut, you'll need some sort of hanger or place the ballscrew on top of the linear rails and make it go through the gantry 20mm plate :D

saves material and very elegant .

all criticisms welcomed / encouraged!

what software are you using? it looks interesting.

CraftyGeek

16-08-2013, 02:40 PM

Interesting approach - but I think it'll work out a lot more more expensive than the current draft above. As it stands above its about £78 material cost...I can't see that aluminium version being in double figures.

CraftyGeek

17-08-2013, 08:55 PM

Bumpety bump for my gantry design above...any thoughts?

JAZZCNC

17-08-2013, 09:15 PM

Bumpety bump for my gantry design above...any thoughts?

Erm.!! . . . It's ok but there's not much holding or supporting that top rail piece. 5mm Ali has no strength in it so your gaining nothing from that really and the Steel plate doesn't add any strength.
The triangle piece on the X axis is about the only thing supporting it and that's not enough it will flex under cutting and transfer to finish quality.
At the very minimum I'd have 2 triangle pieces at each side, really i'd make the gantry sides wider and tie the end of both rails into sides has well as double triangles on each side.

On a plus note you could drop those pieces between the rails and steel has you can drill & tap the steel directly. You only really need those when using Alu profile.

Beef the holding of the cross rails and it will be ok.

JAZZCNC

17-08-2013, 09:29 PM

Thanks Jazz, What about where you are joining the various sections of the steel frame together? I am going to be tapping directly into 3mm wall steel for most of my connections...

Joe I've drilled holes just less than dia of M12 nuts so tight fit then knocked the nuts into holes just below surface with bolt in threads to protect then weld in place then grind welds flush.

Edit: That was for in middle of sections. At the ends were I could reach I just drilled M12 hole for bolt put nut on inside and welded from inside.

JoeHarris

17-08-2013, 10:28 PM

Joe I've drilled holes just less than dia of M12 nuts so tight fit then knocked the nuts into holes just below surface with bolt in threads to protect then weld in place then grind welds flush.

Edit: That was for in middle of sections. At the ends were I could reach I just drilled M12 hole for bolt put nut on inside and welded from inside.

Little more involved than I was Intending but I guess m6 with only 3threads engaged is a bit measly when I think about it! Are those bolts in your photos earlier on this thread m12 then? They look smaller somehow.

On the x axis RHS presumably you don't weld bolts in place - what do you do there? Hope you don't mind giving away all the trade secrets!!

Cheers
Joe

JAZZCNC

17-08-2013, 10:47 PM

Are those bolts in your photos earlier on this thread m12 then? They look smaller somehow.

On the x axis RHS presumably you don't weld bolts in place - what do you do there? Hope you don't mind giving away all the trade secrets!!

Cheers
Joe

Actually they could be M10, I've forgot now but I've still got one frame part built so can check.!!

To be honest Joe I could have saved loads of time and made things easier by just using large hole cutter creating access holes on out side of frame for access with a Socket and bolting together, I just think it looks neater. In your case it may be better to take this route and put rubber grommets in the access holes.

Regards top rails then yes I welded the middle nuts but could have easily done the same thing here. I wasn't concerned if the top rail distorted because I epoxy level the top rails anyway.

Swarfing

17-08-2013, 10:48 PM

JAZZCNC

17-08-2013, 10:54 PM

I've got M12 bolts in 3mm box steel holding bearing blocks in place and never moved?

You Lucky bugger it wouldn't work for me that's for sure it'd strip for sure guaranteed. .:disgust:

Swarfing

17-08-2013, 10:56 PM

Loctited in position and no real forces so fine for my application :whistle:

JAZZCNC

17-08-2013, 11:07 PM

Loctited in position and no real forces so fine for my application :whistle:

Should have known.!! . . . Parcel tape and chewing gum. .:joker:

Swarfing

17-08-2013, 11:18 PM

Jazz my ex misses is on the prowl in wakefield tonight so bang one of your 16mm ballnuts in for me and tell her the backlash is way toooooo sloppy will ya :triumphant:

JAZZCNC

17-08-2013, 11:27 PM

Jazz my ex misses is on the prowl in wakefield tonight so bang one of your 16mm ballnuts in for me and tell her the backlash is way toooooo sloppy will ya :triumphant:

Listen mate been there done all that (well not done her. . Lol) Honestly she's not even worth the words your typing.!!

Swarfing

17-08-2013, 11:32 PM

LOL! why do you think i left her for a CNC machine?

GEOFFREY

17-08-2013, 11:36 PM

Tighter ballnuts and no backlash? G.

Swarfing

17-08-2013, 11:39 PM

Thats the ticket Geoff :thumsup:

JoeHarris

18-08-2013, 07:13 AM

Should have known.!! . . . Parcel tape and chewing gum. .:joker:

Haha cheers guys! Trade secrets eh?!

CraftyGeek

18-08-2013, 09:26 AM

Ok - V2...

Inner end pieces are 15mm plate
Outer end plates are 20mm
bearing blocks also beefed to 20mm
Front plate is still 5mm - more to keep crap away from the leadscrew than perform a major structural role...although should help with twist & sideways flex.
Rear stell plate removed - although that was there more for a convenient flat mounting surface rather than anything majorly structural.

Still comes in under £100 - so that keeps me happy :rugby:

JAZZCNC

18-08-2013, 10:30 AM

Better but still no inner triangle brace.!! See pic of brace on my machine. It's only a small thing but does help stiffen and dampen vibration more than it looks.

Don't let Money run this Build too much because you could easily find you spoil it for not much more money.!! . . . Better waiting and saving up to do it right than skimp. It's a lot of work building a CNC machine and just small things that don't cost the earth can make a big difference.

CraftyGeek

18-08-2013, 10:39 AM

There is one inner brace already - 15mm plate & then 20mm outer on the end.

I'll look at doubling up that inner brace later.

I have to keep an eye on the cost as its already adding up to way more than I originally intended...& its going to take me months & months to sort out the finances for it - so yes, the budget is important. I appreciate that its not worth cutting some corners - but I can't shove a bottomless pit of funds at it.

JAZZCNC

18-08-2013, 11:05 AM

There is one inner brace already - 15mm plate & then 20mm outer on the end.

I'll look at doubling up that inner brace later.

Yep but the more towards the centre you can support it the better, bring that inner triangle inwards the gantry side does the same job so it's not needed there. On mine it's only built like that for ease of fitting it's piece on it's own that bolts on could have easily done it like suggested you do and would work just the same.

I have to keep an eye on the cost as its already adding up to way more than I originally intended...& its going to take me months & months to sort out the finances for it - so yes, the budget is important. I appreciate that its not worth cutting some corners - but I can't shove a bottomless pit of funds at it.

Yep completely agree and understand but just understand it's here at this point when building frame you can't afford to cut corners. If you have a weak structure you have a Weak machine and it will always be weak or hard to correct without major hassle and expense at later date.
I've seen this often where folks think I'll do it on cheap then upgrade later only to find out it's not that simple or easy and end up scrapping and starting again. . . . It's called learning the hard way, I'm just trying to help steer around that.!

CraftyGeek

19-08-2013, 06:11 PM

Right, the gantry is moving along nicely - i'm at the stage now where i'm starting to add the Z-axis. Its probably time to finalize rail/leadscrew choices before I go much further.

My thoughts have been
X - SB20 rail with 2x 1605 screw
Y - SB20 rail with 1605 screw
Z - SB16 rail with 1605 screw

I've seen mentions of clearance issues/fiddlyness when using SB16 with, I assume 1605 screws...should I just use SB20 for Z as well?
All axis will have a single Nema 23 motor & be driven by belts/pinions. Initial power setup will only be 24V - but I plan on upgrading this to at least 48V in the relatively near future.

Does this sound ok?...what about the Z axis setup?

JAZZCNC

19-08-2013, 06:32 PM

No don't use 5mm pitch for X & Y you want 10mm so RM1610. Use Rm1605 on Z axis.

Either rails will work but your correct the 16mm are lower so very close without machining the plates to allow clearance for ballnut.

Dump the 24V ASAP.

CraftyGeek

19-08-2013, 06:50 PM

That'll teach me for posting when i'm tired :-p
Brain said 1610, fingers typed 1605.

Ok - i'll go SB20 all round for simplicity sake.

24V will be upgraded - but it means upgrading the stepper driver boards as well...so it won't happen immediately, but as soon as its possible.

CraftyGeek

21-08-2013, 11:27 AM

As i'm getting further into the design now & tweaking parts sizes to make leadscrew bearing housing line up etc i'm wondering about methods of assembly & tweaking the fit of parts.
This is a 2 pronged question..

Firstly - I see many mentions of shimming parts to get accurate spacings & alignment....what is normally used for shimming?

Secondly - some of the parts that i'll be constructing have a length of steel box with an end cap plate that needs to be welded on.
On the design, i'm drawing this as a neat, flush fit like this:
9594

Given that i'll be completely new to welding (yes i'll be practicing first), the tutorial video that i've watched suggests fitting parts together like the next image so that the actual weld can fit between the box & plate.
9595
That obviously makes getting accurate positioning very tricky & i'm guessing a bit of a nightmare.

So I was wondering if something like this would be a better approach...grind out some notches on the end of the box section - sit the plate flat on the end, then tack weld into the gaps that were created by the grinding...this should help keep alignment more straightforward & accurate?
9596

If i'm missing something here please fill me in...or I could be missing something entirely :nightmare:

Clive S

21-08-2013, 01:31 PM

Could you not just make the green bit a bigger so that you can weld it from the other side to get your fillet weld ..Clive

CraftyGeek

21-08-2013, 03:53 PM

Some of the joints extend on 2 sides of the box already - I guess it might be easier to tweak the layout slightly so they all do that.

mekanik

21-08-2013, 04:31 PM

If you practice on some scrap bits with no gap between & try increasing the Amps so you get better penetration, or try a weld prep on both parts(ie 45deg chamfer)

Gytis

21-08-2013, 04:32 PM

So I was wondering if something like this would be a better approach...grind out some notches on the end of the box section - sit the plate flat on the end, then tack weld into the gaps that were created by the grinding...this should help keep alignment more straightforward & accurate?

what if you weld some wire on inside face and use them like a spacers?,
or just grind the end plate edges to get weld in

CraftyGeek

21-08-2013, 04:57 PM

Thanks chaps - adding a chamfer to the edges could be an option. I'm off work on Friday - I think i'll take a trip to the steel yard & see if I can get some scrap, then have a play with a few different approaches.

mekanik

21-08-2013, 05:05 PM

Just a pity you didn't have a TIG setup, all you do then is strike the arc wait to get your pool and advance the torch, it make a very clean weld.

mekanik

21-08-2013, 05:12 PM

If i were you i would try just putting a prep on the box section, leave the end caps with square edge, then when you lay down your weld you won't(hopefully) melt the outer edge of the blank and it will look a lot better, i am fortunate as i have TIG so can just fuse the two together.
Regards
Mike

JAZZCNC

21-08-2013, 05:15 PM

I wouldn't go running full welds round the edges if they are only for decoration and capping purposes. There will be a lot of heat generated for those welds and you want to keep heat to minimum.

Just chamfer the 4 corners and tack weld into place they will be more than stronger enough.

If you must fully weld then just chamfer the edges. If your on your own with no one to hold then buy some cheap magnet clamps to help.

Edit: Gytis . . if your still reading this then go check your email ASAP please.!!

CraftyGeek

22-08-2013, 08:05 AM

Thanks Jazz - that kind of backs up my first thought.

Another quick Q on the welding front - how much cleaning do you do before welding new mild steel?
I've been searching & keep seeing hugely conflicting opinions - just a quick wire brush & then good to go?

JAZZCNC

22-08-2013, 06:01 PM

Another quick Q on the welding front - how much cleaning do you do before welding new mild steel?
I've been searching & keep seeing hugely conflicting opinions - just a quick wire brush & then good to go?

Well with stick welder then not critical has other forms like Mig-tig etc but still the better you clean the easier it will be to strike up and get good weld.
Just a quick whip over grind or flat wheel is enough just to remove any rust spots etc.

CraftyGeek

23-08-2013, 04:51 PM

So it turns out that welding is quite tricky to master...who'd a thunk?...more practice & video watching required!

At least pillar drill tests with 10mm steel went smoothly - very happy drilling the stuff, but need some new taps.

JAZZCNC

23-08-2013, 05:53 PM

So it turns out that welding is quite tricky to master...who'd a thunk?...more practice & video watching required

Keep trying and it will click and don't get too stressed if your welds don't match those you see on the videos. Even pigeon shity looking will hold more than you realise. Weld 2 pieces together and then try to break the joint you'll be surprised how much effort it takes even with crap looking welds.!!

CraftyGeek

23-08-2013, 06:04 PM

Keep trying and it will click and don't get too stressed if your welds don't match those you see on the videos.

I'm not stressing over it at all - i'll get it...not convinced i've got the current setting nailed yet. Welding lines & dots on a flat surface are coming out nicely - 'T' joins are a bit of a mess but solid. I think i've only used 3 rods so far...another 10 & I might get the hang of it.
Overall though, I like it - very relaxing to do.

JoeHarris

27-08-2013, 03:11 PM

I'm not stressing over it at all - i'll get it...not convinced i've got the current setting nailed yet. Welding lines & dots on a flat surface are coming out nicely - 'T' joins are a bit of a mess but solid. I think i've only used 3 rods so far...another 10 & I might get the hang of it.
Overall though, I like it - very relaxing to do.

Relaxing until you blow your nose after burning a few rods and realise you are coating your insides with filth!

JoeHarris

27-08-2013, 03:17 PM

CraftyGeek

27-08-2013, 03:31 PM

If you can get over the annoying accent there is a guy on YouTube called chucke2009 I think who does some handy trouble shooting videos on stick welding. I found them useful anyhow. Practice is key though I think...

I found his trouble shooting vid at the weekend - that has helped me loads...need to have another quick go, I think I should be sorted after the next practice.
For anyone needing welding help have a look at this...
How To Weld: Stick Weld Troubleshooting - YouTube (http://www.youtube.com/watch?v=akvv4ApYMVE)

I've got a fan set up blowing 'most' of the black crap away from my nose - still got a bit of filth working its way through :-p

Progress report...
Design is still progressing, well on the way now - I should have a more advanced version to show soon.
As the design for the main base frame is finalized, I've bought the steel for the sides & rear brace so at least I can start making some progress on the build. First pieces were cut & drilled over the weekend.

CraftyGeek

28-08-2013, 03:13 PM

Ok - design progress time:welcoming:

The overall machine...base frame is mostly the same as before except for a few minor tweaks - I'll probably add more cross bracing when its built if I feel it needs it (there's plenty of room)
9799

Moving on to the gantry - i've lost count of how many times i've altered the way this fits together...i'm now pretty happy with it - there's nothing offending me there now:peach:
The upper & lower front plates are 5mm aluminium...all other plates/braces are either 15mm or 20mm (ecocast where appropriate).
9796

Back of the gantry is also skinned with 5mm aluminium - 2 sections to allow easier removal around the Y-axis motor mount block. I did try to fit the motor inside the gantry, but there just wasn't quite enough space...by the time limit/home switches are in place I really don't think it'd fit.
9797

Back of the gantry with the rear plates removed for a peek internally. There are a couple of 5mm aluminium plates at either end on the rear of the front faces to help tie them in at the sides (they will bolt to the back of the vertical piece between the main gantry side braces).
The main gantry frame as such is now 75 x 50 x 3 steel box (top, bottom & vertical side blocks)
9798

Z-axis - 20mm plate with rails & leadscrew mounted on the back.
9801

An attempt at a cutaway to show how the whole of the gantry/Y/Z fits together - its tight in there, but everything has at least 2mm clearance except for the Z anti-backlash nut housing which only has 1mm clearance on the back of the Z plate.
9800

X-axis:
2x 1610 leadscrew (1400mm thread length)
SB20 rails - 1500mm
linear bearing spacing - 200mm (outer faces)

Y-axis:
1610 leadscrew (800mm thread length)
SB20 rails - 900mm
linear bearing spacing - 170mm (outer faces)

Z-axis:
1605 leadscrew (350mm thread length)
SB20 rails - 400mm
linear bearing spacing - 170mm (outer faces)

X-axis movement is roughly 1200mm - a smidge under what I was originally aiming for, but acceptable
Y-axis movement is roughly 750mm - a little more than I was aiming for, happy :cool:
Z-axis movement is roughly 180mm - could probably tweak this to gain another 10-20mm.

How does all this look/sound? :suspicion:

Looking for some sort of approval (hopefully :-p) before covering all the parts in holes etc

JAZZCNC

28-08-2013, 03:44 PM

Looking for some sort of approval (hopefully :-p) before covering all the parts in holes etc

Couple things I see and sure I mentioned this one before.? The Rear plate on the Y axis.? . . . It's not required and adds very little strength and actually can cause you problems with binding the bearings if not perfectly flat and edges of mating plates perfectly 90deg. . . . Drop it and save some money and weight.!!

Next is the Z axis motor arrangement.!! Why have you got the motor fastened to the front plate and sticking out the front.?
It looks to me like you have enough length to the Y axis front plate to mount ball-screw on this and fasten motor other way round. Your rails look shorter than the movement range your ball-screw will allow.
If so and it's longer than your Y axis front plate then just do away with the bottom bearing and shorten screw provided it gives enough screw range to use all rail length. On a short Z axis screw you can easily get away with this and it also makes aligning screw/nut that bit easier.!!

Other way is to have longer Y axis front plate and do it this way, both work.!! . . . Either way Your better off with screw and motor has I've described because it will allow higher acceleration from the Z axis which helps if your planning on 2.5/3D work.!!. . . .No point making the motor/drive work harder than needed.!!

Rest looks ok except that I'm not too keen on the low base frame due to large adjustable bed range.!!. . . .Do you really need that much adjustable range because it's compromising the strength quite a bit.?

CraftyGeek

28-08-2013, 04:04 PM

Y-axis rear plate...partly to help keep crap out of the leadscrew etc Thought it would add some extra sideways/diagonal rigidity...can easily drop it.

Z motor - probably didn't think it through quite correctly...with that arrangement, the y axis front plate is considerable shorter than it would need to be to have the leadscrew & motor attached.
The rail lengths are pretty much spot on compared to the screw length - maybe i've got the Z axis linear bearings spaced further apart than needed? (170mm outer face to outer face along the axis). I'll look at swapping the leadscrew & motor to the Y front plate.

Base frame - do you mean raise the lower shelf/surface, or reduce the overall height?
I don't really want to lose much overall height if possible as it will be at a good height for me to work with it at...rather than being low down on the floor like my last mdf machine which was a major pain in the back.
I don't necessarily need all that adjustment - I could raise the lower surface & add more cross bracing to the outer frame?

JAZZCNC

28-08-2013, 06:05 PM

Z motor - probably didn't think it through quite correctly...with that arrangement, the y axis front plate is considerable shorter than it would need to be to have the leadscrew & motor attached.
The rail lengths are pretty much spot on compared to the screw length - maybe i've got the Z axis linear bearings spaced further apart than needed? (170mm outer face to outer face along the axis). I'll look at swapping the leadscrew & motor to the Y front plate.

With 350mm Thread length and only 400mm rails then you have loads of excess thread. You only need enough thread for required travel + ballnut length +10mm or so spare.
RM1605 nuts are approx 50mm in length so for 180mm travel then 250mm thread length is plenty.!

Base frame - do you mean raise the lower shelf/surface, or reduce the overall height?

Yes raise it and widen bracing to match. You don't want to rely on bed frame to form main frame strength, obviously it will add strength but better is main frame is strong enough without.!

CraftyGeek

28-08-2013, 06:15 PM

Yep - sorry, I had another look at the Z-axis screw....I did shorten it earlier - but it looks like I lost that set of changes & didn't think/notice when I was copying the sizes down above.

Have started revising the layout - its fitting together nicer with the z-axis sorted the right way round :-p

I'll do some more tweaking tomorrow - should have a fully revised version then :glee:

CraftyGeek

29-08-2013, 12:56 PM

I've been fiddling with it again :rugby:

Beefed up the diagonal cross bracing on the main frame - all diagonal cross braces are now welded at one end & bolted at the other.
Also rasied the lower surface/shelf - removed the very bottom height adjustment position so it could come up a little further.

I've done a fair amount of tweaking to the gantry & z-axis.
The knock on effect of extending the y-axis front plate to mount the Z motor meant that the z-axis wasn't giving me an optimal range of movement. I had to shorten the height of the gantry (between y rail mounting surfaces) from 200mm to 175mm in order to sort it out - everything is now peachy with a good range of movement & 2mm+ clearances all round. :peach:
Making these tweaks along with removing the rear panel looks to have saved a decent amount of weight from the gantry as a whole :cool:

Am I safe to start peppering the parts with holes & adding pinions etc ?

Edit: Just spotted that the Z rails could now be longer than needed as well...or the bearings might need moving lower.

CraftyGeek

29-08-2013, 01:10 PM

Here's the tweaked Z-axis...ball nut lowered to allow more clearance at the top of the axis & Z rails are now 350mm instead of 400mm.

9902

D-man

29-08-2013, 07:24 PM

CraftyGeek

29-08-2013, 08:40 PM

Personally with you just starting to weld I would urge you to chamfer the two parts to create a 'V'.

Welding can be a tedious venture and without, lots of practise it can take some time to master. So I would not have a gap as you mentioned in image two (I think) as filling gaps with weld is another learning process.

Thanks - think i've got it covered now....been practising a bit on scrap. I'm now at the point where I'm happy to start some of the basic less important pieces to get a bit more experience before getting stuck into anything tricky.

mart154

29-08-2013, 09:20 PM

As I understand you are not too far from me. If you like, I could come and give you some welding tips / help over the weekend.

CraftyGeek

30-08-2013, 09:14 AM

As I understand you are not too far from me. If you like, I could come and give you some welding tips / help over the weekend.

Thanks for the offer - no i'm not far from you. To be honest, I think i'm ok now - after watching more videos over the weekend & working out what I thought I was doing wrong...I tried again very quickly last night - the result is a presentable weld that i'm happy with. If I get find that I run into problems, I may well take you up on that offer - but for now, I think i'm ok :fat:

CraftyGeek

02-09-2013, 10:17 AM

Right given the lack of negative comments on the last revision of my design, i'm starting to move on to the next stage which brings me onto another set of questions...

Gear ratios & microstepping.

After reading around, it seems that the general consensus is that less microsteps are better ie, either use full steps or at most, half steps.
My understanding is that the accuracy of the stepper motor gets lower when the number of microsteps is increased...I think this also has an effect on the torque?

Couple this with the gear ratio from the stepper to the leadscrew makes the choices a little open ended as far as I can tell.
The general flat answer for the ratio that I seem to see is to use 2:1.

I'm only thinking about the X & Y axis at the moment which are both going to use 1610 screws. Belts/pulleys will be 5mm HTD 15mm wide.
Full step geared 2:1 gives a resolution of 0.1mm
Half step geared 2:1 gives 0.05mm
Full step geared 1:1 also gives 0.05mm

0.1mm sounds quite a coarse resolution to me - 0.05mm sounds more like it. So why gear 2:1 & use half step when the same resolution can be had with full steps & 1:1?

or perhaps go for a somewhere inbetween like 1.4:1 (eg 28/20) full stepped = 0.07mm ??

Am I missing something here?

JAZZCNC

02-09-2013, 02:45 PM

After reading around, it seems that the general consensus is that less microsteps are better ie, either use full steps or at most, half steps.
My understanding is that the accuracy of the stepper motor gets lower when the number of microsteps is increased...I think this also has an effect on the torque?

Am I missing something here?

Erm. . . !! You've been the wrong places then.? First you'll struggle to find drives that allow Full step and most start at half.

This is for a good reason. Don't think of MS in terms of increasing resolution but more in-terms of smoothing the motors action.
Full step gives rough action in comparison it's also common for resonance to be a issue if run at full step.
Main reason why you'll see folks run at full step is because they are chasing speed and have slow parallel port so struggle with pulse's needed for higher MS and higher speeds. They are often running low voltage has well.!!

Your PC parallel port will most likely be bottle neck for higher speeds with higher MS. So again you'll probably select the best MS to suit your PP motor/drive combo.! . . . . . If your using Mach3 and you want very Smooth motors and Higher speeds the invest in a Motion control card Like the SS it's well worth the money.

Personally I wouldn't run under 1/4 (800ms) and prefer to run nearer 2000MS which gives much smoother motor performance.
Often your PC and drives coupled with how much machine resonates will mostly determine the best MS to suit for machine.
Every machine tends to have it's own resonance which can affect how the motors/drives perform so you'll probably end up playing with differant settings that suit your machine best.? . . . BUT. . . I can tell you with great confidence you won't run them at Full step or very likely 1/2 has the motor performance will be rough in comparison to higher MS with possible resonance issues to boot with 1/4 or 1/8 being more likely your best option.

Regards the ratio then 2:1 will double torque and resolution of 10mm pitch screw so you won't have any issues here if you do this. It will half the speed thou.!!
If your mainly cutting woods.plastics etc then I suggest running 1:1 for the speed. If your cutting mainly Ali then I'd suggest 5mm pitch and 1:1.

If you want a balance of both then 2:1 would be ok but really not required with 10mm pitch screws if using 3Nm motors with enough voltage (60-70Vdc).