need ideas for worm bearings

Dear ms:

How about a belt and pulley? Or simply changing the kind of motor?

David A. Smith

Worm gears are just flat _not_ low friction devices. Several passes of decent plastic spur gears could be more efficient and not necessarily very noisy.

If you _must_ use a worm gear for whatever reason, you can reduce the friction losses by burnishing the worm and wheel, e.g., running them for a few hours under a slight load with Molykote in oil. Remove the molykote when you're done, or it will keep on burnishing.

Ball bearings, except really cheap ones, don't get noisy unless they're overloaded. Maybe you're preloading them too much; try using a bearing spring instead of shims, and better quality bearings. Regular radial ball bearings are not really optimized for the thrust loads associated with worm gears. You could use larger radial bearings, or angular contact bearings of the same size.

There's _supposed_ to be backlash between the worm and the wheel; otherwise, they overheat. Selecting a large wheel and a small worm gives you less angular backlash for the same tooth clearance.

You can adjust the center distance, bringing the worm closer to the wheel, or you can displace the wheel along its axis (not kosher, but works for light loads) to reduce the backlash below the design value. Reducing the backlash in turn requires bearings with less runout and/or more running-in with the molykote.

At the level of runout you seem to be trying to achieve, you can't use clearance holes and setscrews or keys between gears and shafts; you have to press fit them and use pins or the like.

Also, position the worm at the bottom of the wheel, and run the worm submerged in oil, to reduce friction and carry away any heat generated.

That means the input shaft has to be sealed. Sealed bearings will do, but be sure you don't get the 'non- contact' 'seals', that let the oil leak out.

Or, you could preload the hell out of it and use a bigger motor.

-Mike-

impregnated). nylon and delrin bushings

You could try carbon impregnated PTFE, also molibdonem disulfide filled nylon might be worth a try if the nylon on it's own came close to working.

Thanks to all for the suggestions. The noise is not really the worm/gear meshing, it seems to be the worm rotation in the bushing or bearing rotation. Unfortunately, the design is too far along to change gear trains or change to a belt drive. Also, due to the large reduction ratio and the need to drive a right-angle shaft (due to space limitations), the worm gear drive really is best for the design as it is now. Unfortunately I was handed this design last week in the "11th hour" before commercial release and told to fix the noise/friction problem. If I'd had some input earlier on I could have tried different drive mechanisms. I'll continue experimentation. Thanks again for the input.

"ms" wrote in news: snipped-for-privacy@comcast.com:

Have you looked to a combination bearing? INA makes several variations of combination thrust/radial bearing in one package. You might want to look to something like a needle/thrust. The needle allows a smaller od package. If the shaft is of good material and proper hardness/finish, you can run without an inner race.