Belt drive question

[craigbic]

Is there any benefit to running belt drives from the stepper motors to the lead screws rather than a direct coupling? I have seen it done on a few machines and was wondering if it was worth incorporating into my machine while I'm still early in the building stage.

[craigbic]

Nobody has any input on belt driving the leadscrews versus direct coupling? Come on! This is a fantastic forum full of knowledgeable and experienced DIY CNC fanatics - somebody must have first hand experience or second hand experience or even an opinion!

[jhelmstetter]

Sorry,

I haven't seen any designs where a belt is used to drive a leadscrew unless you are talking about driving a second axis with the belt as in making a model D and using one stepper. I'm guessing it could be done.

I have seen a belt and pulley system connected between two stepper motors (one on each axis) to prevent gantry skew.

I guess my question is why would you want to do it? Usually you would use a belt and pulley system instead of a leadscrew system.

The drawback of a leadscrew system are backlash between the lead nut and screw, lead screw whip at high rpms and long screw lengths, and I'm sure there are more. There are also drawbacks to a belt system. You can encounter backlash between the pulleys and the belts (2 pulleys so two potential problem areas) and under heavy acceleration, the belt may stretch.

If you use a combination of belt/pulley and leadscrew, you are adding more potential problems with no real benefit.

But, if you want to try it out just to do it, why not? Experiement, have fun, learn and pass it on!

If you want to do something different on a RockCliff, try incorporating a rack and pinion system!

They are about on par with start up costs of a good lead screw system. (multi-start lead screw, lead nuts and couplers).

[craigbic]

Thanks for taking the time to reply Joe! Yeah, I was referring to driving the leadscrews not the gantry as in a D model. I can't for the life of me remember where I saw the photos of the machine. Doh! I was thinking that the use of a belt allows one to play with the lead screw speed via reduction. I di manage to find someone who is using chain to drive his lead screws - the noise must be awful! Checkout his machine at:

http://www.thebackshed.com/cnc/RouterA7.asp

I think I made the decision to go with direct coupling instead of belt drive but I still wanted to hear what other more experienced builders thought. I'll leave the rack and pinion drive to one of my future, more advanced builds! I setup my workshop and my partner started making the cuts in the MDF to start our modified 12 x 18-inch A model. I have started assembling the base and Y axis and have taken pictures so far to document. Will post them as soon as possible with more to follow as the build progresses. Thanks!