Timing belt or rack and pinion?

[nzben]

Am designing a table at the moment and been thinking fairly seriously about using a timing belt to drive the x/y axis. I see a few people on here have had reasonable success with chain. I just thought the steel reinforced belt may be a better choice in a dusty environment. They do have a small amount of stretch but run pretty much backlash free, with little friction and very quiet. Not to mention much cheaper than a rack, and not the weight of a chain so wouldn't require as much tension. I'm considering making my table a hybrid with a laser head as well as plasma as I have a couple of 80W lasers floating around and would make it a much more usable machine. Would be nice for the machine to have a certain amount of accuracy for use with the laser.
Would appreciate greatly any input

[jcc3inc]

Sir,

I notice that you are from NZ; so my comments may not fit too well for you. In business, we used gear rack from Standard Steel Specialties,

www.stdsteel.com/gear.html

Pricing for 1/2" x 1/2" x 6 feet length was $23.20 each in quantities of (2) pcs. in Feb., 2006. That was 20 DP, 20 degree Pressure Angle, a stock item they say. We used 24 DP on our machines. As for pinions here in the USA, there are Boston Gear, Martin Gear and Sprocket and others. We had our pinions made for us, and had them nitride hardened as ours was a commercial application.

If you do pursue R & P, there are some suggestions I might have in order to make it a good application. I am at jccinc-at-owc-dot-net

Regards,
Jack C.

[nzben]

Yah - unfortunately being in NZ has those drawbacks from time to time, I priced a rack up at $80 per metre - and I need 8!!! however the place I got the price from is known to be expensive. Although I wasn't thinking of belt drive as a cheap alternative, it's fast and precise, quiet (and cheap!)

Because I was thinking of attaching a laser head also I figured that a belt would have more accuracy than R&P ie - zero and fully repeatable backlash anywhere along the axis, (pretty much all the laser engraving/cutting machines on the market are belt driven) Also has the advantage of mounting the y axis motor to the frame rather than the gantry so you can reduce gantry mass and improve acceleration times.

[MonoNeuron]

Hi NZBEN,
I am nearly 3/4 of the way through my plasma build ( 3m X 4m ) and used 1/2" 0.200 pitch fiberglass reinforced belts for my table but had way too much stretch in them for them to be useful (about 1-2 mm when stopping the head when jogging.) My gantry is way too damn heavy for them weighing in at around 35 - 40 kilos. If you go the belt path then I would suggest 1" wide steel belted. I still love belt drive but I will have to completely redesign my table to use them which I won't do just yet.
I purchased some 1/2 " industrial chain at $1.98 per foot (Reynolds) and tried that but the cogging effect of the sprockets is a bit worrying for me. I will try larger sprockets and see how they go as the small ones do cog too much and a larger diameter I think would be much better. It's about 1/10 th the price of tooth belts but looks promising but probably not much good for your laser system.
Hope your build goes well.
Rich.

[Big John T]

Originally Posted by nzben Am designing a table at the moment and been thinking fairly seriously about using a timing belt to drive the x/y axis. I see a few people on here have had reasonable success with chain. I just thought the steel reinforced belt may be a better choice in a dusty environment. They do have a small amount of stretch but run pretty much backlash free, with little friction and very quiet. Not to mention much cheaper than a rack, and not the weight of a chain so wouldn't require as much tension. I'm considering making my table a hybrid with a laser head as well as plasma as I have a couple of 80W lasers floating around and would make it a much more usable machine. Would be nice for the machine to have a certain amount of accuracy for use with the laser. Would appreciate greatly any input

I just finished my plasma a few months ago and use XL and L belts. The XL are too small and need to be replaced. I used Kevlar cord L belt for the X axis and it works great. Weight and friction play into the choice of belts. I used an under the bearing over the pulley and back under the bearing routing with fixed on each end. The ends are adjustable for tension and racking for the Y axis. As you tension the belts your gear ratio changes ever so slightly as you still have the same number of teeth per revolution's on your sprocket. Checked with a dial indicator I needed to change the calculated steps per inch from 4000 to 3996... not much to worry about but there. IF you can keep the rolling weight down and the movement smooth then belts work great.

John