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View Full Version : Best place to buy parts for a cheap first CNC.



Boscoe
16-07-2013, 04:01 PM
So I am looking to build a CNC machine designed for cutting wood and aluminium. I haven't fully decided but I think I want a cutting area of about 750mm x 500mm. I don't have any access to any milling machines currently and so would like to buy a Z axis kit to make sure it's good. I'm only a real budget because I'm a student and so probably have around 750 to spend over around 6 months so this will be a gradual long term project. I plan to use supported rail and timing belts for cost, if it's worth it I will go with screws. I've been looking around and ebay seems to be the cheapest place to buy this sort of stuff (I need everything) however I think I will put an advert in the wanted section to see if anyone has anything second hand.

I'm an electronic engineer and very skillful with my hands and designing mechanical objects so a challenge is not scary!

Thanks
Boscoe.

Jonathan
16-07-2013, 07:13 PM
You wont cut aluminium using timing belts and no screws, it's simply not stiff enough. 750 is probably just about enough to make the machine with ballscrews, but not if you have to pay people to make parts.

martin54
16-07-2013, 07:15 PM
Welcome to the forum, have a read through some of the build logs to get you started, you may well find you need to look at building it over a longer time period so you can save more money for the project.

Boscoe
16-07-2013, 07:16 PM
You wont cut aluminium using timing belts and no screws, it's simply not stiff enough. 750 is probably just about enough to make the machine with ballscrews, but not if you have to pay people to make parts.

Not even if I use wide belts?

Boscoe
16-07-2013, 07:17 PM
Is ebay the best place to get cheap items? Is the quality of the items acceptable?

Jonathan
16-07-2013, 07:20 PM
Not even if I use wide belts?

Maybe, but I expect you'd end up paying more for the belts then the ballscrews. In addition you'd need to gear the motor down substantially to get enough resolution.


Is ebay the best place to get cheap items? Is the quality of the items acceptable?

Often it is, but there's also AliExpress.com - Online Shopping for Electronics, Fashion, Home & Garden, Toys & Sports, Automobiles from China. (http://www.aliexpress.com). Quality of the ballscrews I've had from eBay has been perfectly adequate.

Boscoe
16-07-2013, 07:37 PM
Maybe, but I expect you'd end up paying more for the belts then the ballscrews. In addition you'd need to gear the motor down substantially to get enough resolution.



Often it is, but there's also AliExpress.com - Online Shopping for Electronics, Fashion, Home & Garden, Toys & Sports, Automobiles from China. (http://www.aliexpress.com). Quality of the ballscrews I've had from eBay has been perfectly adequate.

Wow it's a lot cheaper on there. Is there something I should look out for?

birchy
16-07-2013, 07:53 PM
I've just bought ballscrews and ballnuts from Chai on eBay (http://www.ebay.co.uk/sch/linearmotionbearings2008/m.html). Very cheap, very fast delivery (3 days from China) AND they'll machine the ballscrews for you to a high standard for next to nothing. You're looking at about 150 for 3 ballscrews, ballnuts, bearing blocks and machining, including shipping. Bargain!

JAZZCNC
16-07-2013, 11:00 PM
very fast delivery (3 days from China)

Wow Birchy think you have the record there at 3 days delivery, thought Chai getting stuff to me in 4 days was a record..:applouse:


Not even if I use wide belts?

Yes they will cut aluminium ok see this machine I built for a guy using 15mm Belts and alu profile scrounged. It's cut every thing from Alu to PCB's. It went to Ireland so not seen it since left my hands but it's still going strong I believe and without any issues other than the initial setup and settling down.
New Machine Build Belt Driven extrusion framed wee beasty!! (http://www.cnczone.com/forums/cnc_wood_router_project_log/108333-belt_driven_extrusion_framed_wee_beasty.html)

That said Jonathans spot-on It's actually cheaper and far easier to buy Ballscrews from chia. We had the stuff or got it cheap but if building again it would have screws has by time you bought bearing,housing, belt, pulleys etc they will cost more.
By far the best and quickest for someone new is buying screws and BK/BF bearings pre-machined from Chai. It's basicly makes it a simple bolt on affair.

By far the easist hole to fall down is the Electrics, it's also the most important to get right.
DONT buy the cheap ALL-IN-ONE TB chip based boards you see on Ebay they are bad news.
Like wise be careful of some of the kits which sell motors, drives, BOB(breakout board), PSU etc.!! Often the motors and drives are ok but the PSU is under sized and the BOB rubbish quality.
PSU size or more importantly Voltage makes a big difference to performance you'll get from a stepper and often they'll sell drives which are rated at 50v and can run comfortably at 46-48 along with motors which can take much higher voltage than that but supply a 36V PSU.
Not much difference you'd think but to a stepper it can mean upto 1/4 less usable speed/torque than 48V would give. Poor quality BOB can give you night mares and many wasted hours chasing problems.

Regards linear rails then you can also get these from Chai has well. Don't be tempted to buy unsupported rails you'll only regret it.

Best advise is don't buy anything until you 100% know it's what you need and will do the Job. Ask if not sure.!!
Also while it's inspiring and tempting to see motors spinning on bench Don't buy electrics until you need to fit them on machine, they only have 1 year warranty and can fail in use so you want them last of all.
Same goes with spindle, it won't be needed until your ready to cut which could be weeks at best and most likely months.

Good luck.

Web Goblin
17-07-2013, 07:19 AM
I wouldnt recommend belts. I remember once working on a plasma machine with twin X axis belt drives. 50mm wide reinforced belts. Major pain to get the machine square and keep it that way.