Zero backlash gears

[vadeem]

http://www.orientalmotor.com/in_motion/october_2004.htm

This page shows some zero backlash gearing for stepper motors. Can we use any of this to our advantage?

[Gerald_D]

Thanks for that link vadeem, it cleared up the mystery of the "Taper Hob" gear for me.

Sure, you can use it, but I don't know if there will be a significant advantage compared to the cost. The MechMate style machine doesn't particularly have a backlash problem, so I don't think you need to look for a cure.

[Greg Waggy]

CNCZone has a thread dedicated to this topic.

http://www.cnczone.com/forums/showthread.php?t=20527

[Gerald_D]

Greg, that CNCzone discussion is purely on backlash for screw driven axes. Backlash on low-cost screws is a big problem and a reason for a MechMate to use spring-loaded rack & pinion instead. A MechMate with pinions direct on the motor shaft has zero backlash. Period.

The folk using the standard gearboxes from Oriental Motor, also with spring-loaded rack & pinions, are not complaining of backlash either. But I have no personal experience of it. That is something that I still want to try for myself - my gut feel is that it will be fine.

[Greg Waggy]

It uses the same prencipal, spring loading on the threads. Your's is a lot more simple if in fact there is zero backlash. With what I have in mind for building, I'll be using both ACME rod and rack and pinion systems, so I need all the input I can get.

[Sheldon Dingwall]

I haven't measured it, but there's a lot more play in my gearboxes now than when they were new.

[Mike Richards]

The gearbox offering from Oriental Motor is only available on some of their $$$ motors. The motor/driver/gearbox combination cost more than $2,200 when I last checked. After-market gearboxes with basically the same specs can be found at www.baysidemotion.com (http://www.baysidemotion.com). Their gearboxes are in the $700 to $1,000 range.

Ballscrews with double nuts usually can be adjusted to near-zero backlash. Since typical ball-screws aready have a 5:1 ratio, doubling or tripling the ratio can be done with a belt-drive gearbox. By the way, a 5:1 ball screw would require 10,000 steps from a Gecko driver to move one inch. On a non-geared rack/pinion machine using a 1-inch pitch diameter spur gear (20-tooth, 20-pitch), it only takes about 636.94 steps to move one inch, meaning that resolution on a non-geared r/p is 0.00157 inches while resolution on the 5:1 ball screw would be 0.0001 inches - or 15.7 X better than the r/p. (Be aware that there are many other factors that make ball-screws less atractive on a CNC-router. A rack/pinion system is relatively accurate, robust, simple to maintain and inexpensive to build. I haven't found the need to improve the resolution when cutting wood products - that start warping the second after I take them off the Shopbot.)