Timings Pulleys and belts

[mocnc]

ok, I am getting the feeling that ppl like the Timings Pulleys and belt system due to the very little backlash. So is this better then a worm gear/gear system? I am designing a 4th axis system for my cnc. I was thinking about getting a small rotary table but they seem to be kinda expensive. I have seen ppl convert a sherline rotary table to be used as a 4th axis. Once again cost is an issue here for me, they sell for around $150+ american. Living in canada makes it a little more out of reach due to the shipping/exchange. I am trying to make one that uses a 3 or 4 chuck head stock, with a 3 or 4 chuck tail stock. Simular to the ones used on lathes but only at a smaller scale. I want to be able to cut pool cues with my cnc and also be able to do some inlaying/carving on the cues. So hence thats why I would like a 4 axis with a stepper motor attached. Any ideas?? Where is a good place to get timing pulleys/belts for our diy cnc? How about worm gears/gears. I have heard about a company called boston gears, are they any good? Does anyone have they web site address for it, or for anything that could help me my designing?

[HuFlungDung]

/me resists urge to curse and flame

You might want to check this thread started by you on this topic a few days ago
Links to worm gears for 4th axis

Also, keep in mind that direct-driving an indexing head with belt and pulley is going to result in a loss of precision at the work piece. Also, a worm gear system tends to have better self-locking characteristics that help prevent your cutters from getting a tooth on the work, and taking it for a "surprise spin"

[ViperTX]

Well heck....if you want cheap...then buy a lathe headstock/spindle and attach a 3 jaw chuck with the same type of clamping mechanism as a Nova chuck (used in wood turning)....drive the lathe spindle using one of the back gears.

2nd option...buy a used wood turning lathe....like a jet Mini or something small like that and adapt the drive.

3rd more costly option....bench centers....

[chuckknigh]

I've been thinking -- always dangerous for me. :-)

I ran across this site a while back...
http://www.scrollerwheel.com

It describes a bearing/gearing system which utilizes ONLY rolling friction, so it's virtually friction free. A chuck mounted on a central output shaft could be fed from one of the planetary rollers, and ANY gearing ratio could be implemented. Just vary the size of the input/output rollers accordingly.

It looks quite simple to build. In fact, I just got back from Fry's. I've got some copper wire and some heat shrink tubing...guess what I'll be doing in my occasional free time? Making bearing assemblies to play with!

-- Chuck Knight

[chuckknigh]

This shows a picture/rendering of one of their scroller assemblies. Seems like it'd be relatively immune to contamination, too, unlike anything that requires grease!

-- Chuck Knight

[Al_The_Man]

I wonder how that compares to the rolling-ring type of drive,which has been around for a few decades. it seems it might be along those lines. Nice to see an invention coming from this side of the border though .
Al

[chuckknigh]

Well, I've gathered some parts, and given a little free time, will be building a few of these bearing assemblies. Might even try a few with various gearing ratios.

Just need to figure out how to shrink the heat-shrink tubing that I'll be using for belts...I don't have a heat gun, and I'm not sure my blow-dryer puts out enough hot air to activate it. My bachelor's is in political science, but even *I* don't put out enough hot air to shrink it! :-)

-- Chuck Knight