New Machine Build- Brett's Desktop 3-Axis

[brettneale]

Hey all, first post here but I've been reading up on a heap of stuff (I'm really enjoying all the updates on Widgitmaster's machines lately!). Anyways, I've been bitten by the bug and have decided to build a small 3-axis desktop mill. I recently graduated from uni last year as a MechEng, so I'm always designing stuff and this seemed like a perfect project for me!

Anyways, first the design. Being a desktop mill, I was after something compact with a similar size to Widgetmaster's Midi router. It'll be great for PCBs and small parts for some racing simulator parts I plan on machining. The size was also dependent on what size linear rails I could source on eBay, and I tried to maximise the cutting area available for any given rail. In the end, total cutting area is at:

370mm X-Axis Travel
215mm Y-Axis Travel
73mm Z-Axis Travel

The whole thing will be 10mm thick aluminium plate except the Z-Axis block and the router clamps which are a bit thicker. All axes have THK linear rails - SR20 on the X, RSR12 on the Y and SR15 on the Z. They were all under AU$100 delivered per pair, so I'm quite happy with those buys...

Other stuff I've sourced so far include:
- Kelinginc 40V 6.6A power supply
- Kelinginc breakout board
- 1/2"-10 1-start ACME leadscrews and Widgitmaster delrin nuts
- 1/4" shaft couplers (guys in Australia - Jaycar have em for a decent price)
- Bearings for the leadscrews

I've also got the 25-series 8020 extrusions for the table in the mail. The spindle will be a Ozito plunge router, interchangeable for a Dremel when I get around to buying one. All the machining will be done by a friend-of-a-friend who's developed some fishing reel thing that I'll do the technical drawings for in return (I'm employed as an engineer and mechanical drafter at the moment).

One thing that has bitten me though is the stepper motors. I bought 3 steppers first up before I'd done my research (bad idea) and they're going to be too small I think (they're only 56 oz-in). Also, I got reamed by Australia Post who decided my package looked good to their subcontractor delivering it and I lost my 3x 2A stepper drivers I bought on eBay... So anyways, I'm thinking of forking out and buying 3x 260 oz-in steppers and 3x stepper drivers from Probotix, which would set me back about AU$280 by the time it's shipped here. Hopefully I can get some sort of reimbursement out of Australia Post for my $100 worth of stepper drivers argh! Anyone have any cheaper/better options for a machine as small as this one?

Anyways, I've got a few CAD pics of each axis and the assembly. The Z-Axis has since been refined and the spindle has been added since I took these shots.

[Kipper]

Hi Brett, I think you'll need some more carriages (trucks?) nice drawings though

[brettneale]

Originally Posted by Kipper Hi Brett, I think you'll need some more carriages (trucks?) nice drawings though

Yeah I tried to get the right THK rails for the job, which I reckon I've done. The thing won't be very big or heavy, and the X rails are way over the top of what is needed. Having less trucks has allowed more travel for the same rail length, which is what I was after. I've checked out the specs in terms of force and moment ratings and these rails are definitely up to the job!

[brettneale]

Well turns out my stepper drivers were found today, so all I need now is motors. Would 200 oz-in be suitable for a machine this big? I'm not after production-like rapids or cutting speeds...

[Kipper]

200 ounce inch = 1.4 newton meter, I see no reason why not! And if you're using nema23 motors you can upgrade those at a later date to get those rapids if they elude you. What ballscrews allthread etc are you using?

[twistedfuse]

Brett,

Nice design. I agree with kipper tho, but only for the main axis. I have seen a few commercial machines at the sydney expo. I did notice that a few did have only one to carry the gantry but these were mainly pcb manufacture machines. So if you are planning to do anything more i would add a secondtruck either side to help with the moments about these gantry, beause you will see the chatter in fine detail. Really nice design and nice compact size. I too am building a small machine as my next build and building around what i can get. Ballscrews are hard, what will you use?
Daniel

[twistedfuse]

Well It must beone of those nights. Just re-read everything and answered alot of the questions. The x axis rails at SR20 should sustain most of the chatter if it is medium to high preloaded from what i can see. AS for the z axis is it possible to find out where you got your small rails at such a good price.(EBAY?).

I'd also like to hear how the leadscrews with widgitmasters nuts work. I want to install ballscrews but see it better to try with leadscrews first and then re-fit ballscrews later. Guess its time to start scouting ebay for deals. lol.

Keep up the great work, will be following your build. Hopefully we might be able to help each other.

Daniel

[twistedfuse]

Sorry forgot one last thing. If you havent already try and steer clear of the joiners from jaycar. I bought them and found them to be more hassle than worth. There is slight backlash to start and the middle rubber coupler wears out really fast. Would be good idea if you do to CAD/CAM the middle joiner and make another one from HDPE/Delrin which might help and stop alot of the problems i had. I ended up getting some help from a regular lifesaver on these forums and they were proper lovejoy connectors. Try for these if you can.

Daniel

[brettneale]

Kipper:
I've got 1/2"-10 1-start ACME screws with delrin nuts, so I don't think the torque will be a problem. Thanks for confirming 200 oz-in motors as something workable!

Daniel:
I scored all the rails from eBay, but had to look in the US for the SR's for the X and Z. The SR20's are a really beefy rail and I'm sure they'll take the moments fine. With eBay it's all about waiting until the right rail comes along with the right length, the right type, and most importantly the right price! A sniper app like JBidWatcher would be really useful if you want to avoid bidding wars. And I managed to get heaps of stuff cheaper from the US even after postage since the conversion rate is so good at the moment.

Thanks for the heads-up about the Jaycar couplings. I know they're a bit cheap, but they're accessible and would be fine to get the machine up and running. Any idea where my best bet would be to get some Lovejoys?

[twistedfuse]

Brett,

The rails sound great and will have to look into that program for bidding. Would help greatly especially since i just lost a bid overnight on a perfect ballscrew mainly because it was finished at 3am last night. Even tho it asks for your max bid i hold off a bit before hand. Ah well many more to come im sure. As for rails im only after some short small rails for a z axis. I obtained some old stock a while back and they are 25mm rails. They will be perfect for my next 2 machines. I have just started my blog on my second and wont be long till the 3rd.

Where did you get your ACME screw? Did you get them from widgit too? As for the lovejoy couplers. Surprisingly they arent much dearer than the ones from Jaycar. I dont want to drop names about who got them for me but if you browe my first machine build im sure you can find out who and talk to them about where he got them. I think they were $17 each. You might need a lathe to bore them out tho if you want a custom size bore. There are some helical bellow type couplers on ebay but the loveloys would be much better with the flexi coupling.

http://www.industrialbearingsupplies.com.au

These guys have them but i dont know prices. Also there was a company in sydney that i saw once that had them and can only guess that tea transmissions and NSK would probably have them too, but not sure about price, im sure they might be a little dearer.

Daniel

[brettneale]

Thanks again Daniel! I'll have to look into them.

As for the ACME screws, I got them on US eBay. There's a store on there called Precision CNC Router who have 2 types of screw in a few lengths, machined on the ends for 5/8" bearings and a 1/4" part for the coupler. However I'll be machining those down a bit more so I can put locknuts on the bearings and to get them the right length. They were quite cheap too, they combine shipping and do custom orders too (they sell them with Delrin nuts, but you can request they ship without them).

[brettneale]

It looks as though my machining deal may fall through, and this thing is taking forever! Since I have no machine shop at home, I'm thinking of building this in 16 or 20mm MDF just to get it going, then change bits to ally as I go. It may not be the stiffest or most elegant way of doing it, but I've spent enough on this so far and it'd be great to get it going and iron out all the bugs (which I'm sure there will be plenty!). I'll also order the Probotix steppers next week which should hopefully complete my electronics (may need to solder up some simple current limiters...).

Might do some FEA this weekend and see what the MDF will do for me.