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View Full Version : using chain for gantry movement?



CNC Darren
10-25-2004, 04:25 PM
A friend of mine saw my router table and wondered how hard it would be to build a biger one. We started kicking around a few ideas and with such a long table we were thinking of ways to get around using a long lead screw. I brought up timing belts and because I have seen them done before but they are kinda pricey. We both came up with the idea of using bicycle chain instead done the way I have seen most timing belts done, pully mounted on a shaft in the gantry and the belt mounted to the table. Could the same be done with inexpensive bike chain? Length is no problem as more can be linked on and there may be a little strech at first but the mount would be made adjustable to take up the slack. Were not looking for super accuracy but good enough for a wood router. so what do you guys think? would it work?

jeffery71
10-25-2004, 04:50 PM
Sounds like it would work.. I've heard others talk about doing it that way. I think I would prefer rack and pinion over chain though. My current table has rack and pinion.

Jeff

svenakela
10-25-2004, 05:27 PM
A chain has, even when tentioned, a very low accuracy. And beleive it or not, a chain comes with a remarkable power loss. Go with the cheapest Acme's and a homemade plastic nut, it will probably give a better price/quality ratio.

Cheers,
Sven

chuckknigh
10-25-2004, 06:30 PM
Actually, bicycle chain, when properly tensioned, maintained, lubricated, etc has a transfer efficiency of over 90%.

That's assuming a LOT, though.

There was a thread on DIY-CNC which dealt with chain vs belts vs racks vs screw drives, and the chain fared pretty well. But, because of other considerations like stretch and pinion wear, it was dismissed in favor of rack and pinion drives for long axes.

-- Chuck Knight

svenakela
10-25-2004, 07:36 PM
A chain with less power loss than 10% is far more expensive than a screw, believe me.

--Sven

CNC Darren
10-25-2004, 08:36 PM
Ok, so if we went with a rack and pinion what does everybody use for that?

chuckknigh
10-25-2004, 11:19 PM
A chain with less power loss than 10% is far more expensive than a screw, believe me.

You'll get no arguement from me, but there are *other* design considerations than just cost, when designing a machine.

It could be that, for someone, a chain is a proper engineering decision. It's always good to have options, and that's probably why he asked this question in the first place.

And, just for reference, I've seen a chain drive CNC router on the net...according to the web site it worked quite well, with great repeatability. Wish I'd saved the URL.

-- Chuck Knight

ynneb
10-25-2004, 11:32 PM
Go the chain, be adventurous. Ive considered it myself b4.
If it doesnt work let me know and ill give it a miss. :)

You must remember that many of the comments you will get in this forum are from purists who consider 1/10 th of a mm to be devistating.

If like you say, your just going to cut wood I recon it would be fine. But dont hit me if it doesnt work.

HuFlungDung
10-25-2004, 11:37 PM
Chains don't stretch, they wear and it looks like stretching.

A stationary chain is not going to stretch appreciably. A chain normally wears rapidly because it is flexing around the sprockets.

Whether a new piece of chain is "right on" the nominal pitch, I don't know. I also don't know if the mesh of a sprocket with a chain (especially in "rack mode") is free of periodic errors. That would mean slight speed up/slowdown or plain old backlash as each tooth engages the roller, if the mesh of the sprocket isn't well controlled.

sol
10-26-2004, 07:47 AM
Ok, so if we went with a rack and pinion what does everybody use for that?


http://cnczone.com/forums/showthread.php?t=6022&highlight=rack

Here is a good previous discussion of rack and pinion...FWIW I am using the older 14.5 and it seems okay, but then the machine is not being used all day every day. :)

CNC Darren
10-26-2004, 04:53 PM
well i tlakied to him today and it sounds like he is set on chain, with the design made so that if the chain doesnt work then we could make the swap to belts. The design that we have so far could even use rack and pinion with out to much work. I'll be sure to post and let everyone know how well it does. Thanks for all your replies

ynneb
10-26-2004, 09:41 PM
Originally posted by chuck in another thread.

More here http://users.adelphia.net/~northeastair/album/machine.html

http://users.adelphia.net/~northeastair/album/machine_images/cnc3.jpg

CNC Darren
10-26-2004, 10:51 PM
well I think thats close enough hes using chain to turn lead screws but I would thing there would be a whole lot of difference in using it to run the gantry since he would still see any wear or strech in the system.