Re: Backlash
 

You can make a pocket in your gears on a lathe, and tolerances to .001 or better should be easy with just a little care. .001 interference in aluminum is a pretty tight fit, .0005 for a 1.5" OD bearing would be plenty. You can fiddle this a bit with sandpaper or a file.

For clearance between teeth, you must be sure there is no negative clearance (too close together). The higher the speed, the closer the tolerance, the harder the material, the closer they can be. For moderate speeds (1000 RPM-ish) in aluminum, .0005-.002 is fine, be sure to run the gears in for several hours with light lubrication, in both directions and light load.

When making intermittent cuts (like turning hex to round) don't use carbide bits, regular tool steel will manage that better. Carbide tends to shatter, especially the ones with the little triangular inserts.

An arbor press is convenient, but not required. The reason to avoid using a hammer is the shock loads being transmitted. Better use a vice or some clamps with metal blocks than a hammer, but if unavoidable, go slowly with the hammer.

Cheap bearings are OK for low speeds (600 RPM-ish) and sloppy tolerances. ABEC bearings are great for higher speeds (10,000 RPM) and longevity, as well as tighter tolerances. I buy bearings on eBay all the time, but if you have a bunch of useable bearings, use them.

Old trick if the pockets are accidentally a loose fit: Make a plug for the hole from scrap metal, then drill three (or more) evenly-spaced 1/8" or so holes in the edge of the bearing pocket, with the holes protruding maybe 0.010 into the pocket (and hole plug). Fill the 1/8" holes with metal rod, file them down on the inside a little bit to get your press fit.

Don

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I believe the only bit we have ever used for our lathe is a carbide. There must be some tool steel ones laying around somewhere...

That is a pretty nifty trick about the hole plugging! Never would have thought of that.

Our mill has a digital readout that goes to .0005 (with the last digit being either 5 or 0). Now that is 25 times what I estimated the tolerance to be (I believe the digital readout is a Bausch and laumb). I will have to find out the actual tolerance next time I go to our workshop.

thanks, Vivek

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If you want an alternative to flanged bearings you can make your own support for the bearing out of button head screws. Here is a picture of how I do it. http://www.chiefdelphi.com/media/photos/16362.

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With steel, I would say that would be fine, but with aluminum it would wear out fast. Another idea... what about brass bushings.

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We have typically used a 0.08 mm increase in gear center distance with our custom-made geartrains. My guess is that this is on the high side compared to some others who make their own boxes, but these are typically wire-edm'd gears whose surface finish is a little rough before run-in. Our gears are not very wide either.

We run them in at no load (i.e., not driving the chassis around, but just running the wheel while it is off the ground) for an hour or so. We have been using the same tube of Amsoil grease (apparently its "racin' grease" :)) for several years now....

If I was using purchased, nicely finished, wider gears, I think something in the 0.05 mm range would be my choice for the amount that the center distance is increased.

The looser distances like I am suggesting here make the boxes easier to assemble and get low geartrain friction, in my opinion.

Ken

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In my opinion, Ken is THE expert on this subject.

I recommend everyone interested in high-efficiency gearboxes takes a close look at the practices he recommends. (You'll also find any other tid-bits of advice you can get out of him to be HUGELY beneficial.)

"Ain't nothing that rings like a Huskie..."

-John

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So if I were to put two gears right next to each other, I would put a distance of .002" between them or .004"? .002"=~.05 mm

thanks, Vivek

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That sounds like a pretty good idea. Would you recommend threading the aluminum itself or doing a through bolt? It seems like just threading the aluminum should be plenty strong.

thanks, Vivek

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I can't imagine that you'd have any problem with just threading the aluminum, if the button-head screws are just for holding the bearings in. Furthermore, it could be difficult to do through bolts unless you are using insanely small gears (smaller gear diameter than outside bearing diameter)

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.002"
Ken is referrring to the center to center distance.

<edit>Baker recommends the same in this blast from the past... http://www.chiefdelphi.com/forums/sh...0&postcount=11 </edit>

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I thread the aluminum and use #10-24 button head screws. Center of tapped hole is (radius of bearing plus 1/8") from center of bearing.

I have built all my gearboxes at nominal center to center for the gears. I also run for 5-10 minutes with the wheels off the ground for break in without lube, than lube with lubriplate and run on the ground.

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Yup. Mark has it right, as usual :)