belt driven CNC table? (I have pictures)

[rcbamm]

Originally Posted by martinw Dear Kipper, Thanks for that. I do not wish to sound ungrateful, but the belt stretch stuff could still be an issue. I'm pre-judging it, sorry. Will take a peek really shortly. Thanks again.. Best wishes Martin

I thought about the belt stretching.... but then, I'm only gonna be cutting mostly foam and balsa wood. once I get my table working properly and precise then I will try out some hardwood for firewalls and landing gear plates etc.. but if I can start cutting foam and balsa wood I will be a happy man

[ger21]

Originally Posted by Kipper If anyone wants to express an opinion (I've been wrong before lol) and I'm actually on topic for once Attached is a rack type system that seems "awfully good" Very generous .zip file size allowed! admin.

Make sure you're sitting down when you get the price.

[ger21]

Originally Posted by rcbamm I thought about the belt stretching.... but then, I'm only gonna be cutting mostly foam and balsa wood. once I get my table working properly and precise then I will try out some hardwood for firewalls and landing gear plates etc.. but if I can start cutting foam and balsa wood I will be a happy man

Check out www.sdp-si.com for a lot of good belt info.

If you take a look at the threads from Joe's design router, they're all using or switching to 1/2-8 2 start acme. Best performance for the price, and easier to implement than a belt drive.

Just a guess, but I'd say at least 90%-95% of the homebuilt routers here use acme screws with great results.

With a belt drive, you'll likely need a gear reduction which adds to the complexity.

[rcbamm]

this is what I have in mind for right now....

package: CNC 3 axis Stepper motor Drive system http://cgi.ebay.com/CNC-3-axis-Stepp...QQcmdZViewItem


belt: about 20ft of the 3/8" WIDE 0.20XL open ended timing belt.

Pully for stepper motor: 15 teeth 1/4" bor .2p http://cgi.ebay.com/CNC-Timing-pulle...QQcmdZViewItem


reduction pully: i would probably get three of these and put them side by side for reduction then the other one for the belt drive. the third one would be for the return pully on the end of the router table. 30 Teeth 1/4" bore timing pully. http://cgi.ebay.com/CNC-Timing-Pulle...QQcmdZViewItem

and probably a 60 tooth kevlar timing belt for the reduction. http://cgi.ebay.com/CNC-TIMING-BELT-...QQcmdZViewItem


I add this all up two times so I can have every thing for the Y rail aswell.


how does this look?


-Dan

[harryn]

Hi - I am in the "studying / planning " stage of a belt drive setup as well.

I did a search of the forums, and someone (sorry, cannot remember who to credit) pointed to these guys.

http://www.brecoflex.com/?CATID=1&SC...T10&codeName=M

After a lot of reading of there site, it seems that the belt company recommends
- The AT style tooth
- I picked the -10 series (for powerful tooth strength)
- Steel reinforced for minimizing stretch
- They also have a special tolerance tooth shape for reduced backlash applications (3 actually, 1 std, 1 better, 1 best)
- The tighter tolerance belt teeth also match better tolerance pulleys

Interestingly, they claim that the steel reinforced versions do not need stretch compensation, just "pre-tension".

Belts are in every size you can imagine, up to 6 in wide.

I have not yet priced them out, so that part is still open for sticker shock, but my initial thinking is to use 100mm (4 in wide) so that the the belt can take up some of the (likely) slop / vibration in the system. Some of this is of course wishful thinking.

[martinw]

Originally Posted by rcbamm I thought about the belt stretching.... but then, I'm only gonna be cutting mostly foam and balsa wood. once I get my table working properly and precise then I will try out some hardwood for firewalls and landing gear plates etc.. but if I can start cutting foam and balsa wood I will be a happy man

Dear rcbamm,

I didn't wish to pour cold water on the entire idea of belt drives. Far better men than me have had good results.

If you take a peek into the guts of $70 ink-jet printer, you will see a tiny belt driving the print head. The print head sprays stuff with incredible accuracy.

Good luck,

Best wishes,

Martin

Martin

[randyf1965]

harryn,

Any pricing from http://www.brecoflex.com/?CATID=1&SC...T10&codeName=M ???

I want to do a belt drive is 3/8" wide enough for the y axis? MIne is 65" wide so I was looking at 3/4"

[harryn]

Hi - I have not asked for pricing yet.

The belt drive site has a calculation setup for belt selection - I have not run the numbers yet. I think it has more to do with how much force you need than Y dimension.

I made an guess (based on comments in threads by others) that the gantry would have a mass approx 50 Kg / 100 lbs, and be driven by at least a size 23 motor, or in my case, more likely a size 34 - so approx 400 - 500 oz - in of torque. Only logic is that is what other people seem to be using.

I am toying with using a really wide belt (2 x for each axis) so that the belt tends to help stabilize things, at least that is the idea - so I am thinking 3 or 4 inches wide. Probably way overkill, and the idea might die once budget reality starts to hit.

[studysession]

I did a belt drive system:
http://www.cnczone.com/forums/showthread.php?t=39813

It doesn't look like much but it works.

[vline5]

With only a hundred pound gantry I don't think you would need a 2in wide belt if your driving it on both sides of the gantry. check out the specs on the belts. they handle more than it appears.

[sonicwonder2000]

Just a note: you can cut looped belts to create an open belt. I am currently in the midst of building a belt drive system myself. My understanding is that the belts stretch and rebound only at very high accelerations. Keep your acceleration down, and you can still rapid at high speeds (300 ipm+).

[ger21]

Originally Posted by sonicwonder2000 Keep your acceleration down, and you can still rapid at high speeds (300 ipm+).

Except that in most cases, faster acceleration is preferable to faster rapids.