Adjusting Z-axis knee backlash (bevel gear)

berga · Apr 22, 2019

Hi all,

I reassembled my knee after a painting project. Interestingly, the Z-axis hand crank now makes a grinding noise typical of overly-tight backlash adjustment. The two bevel gears are very obviously too tight.

How is this adjusted? I tried loosening the set screw on the upper bevel gear, but it appears to be slid all the way outwards. Truthfully I don't understand how the entire assembly is constrained; the bearing seems to "float" in the casting. I also tried smacking the entire shaft outwards with a rubber mallet, to no avail. Any other suggestions?

wheels17 · Apr 22, 2019

I just had to replace a pair of missing bevel gears in a shaper based on one broken, incomplete gear section.
The Boston Gear catalog at https://www.bostongear.com/-/media/Files/Literature/Brand/boston-gear/catalogs/p-1930-bg.ashx was very helpful. Miter and bevel gears start on page 71 of that .pdf.

Both gears need to be equidistant from the shaft intersection at the proper dimension for the particular gear. Both will probably need to be adjusted for the best performance. If you count the number of teeth and the diameter, you can probably find a standard gear in their catalog that will match, and the catalog lists the proper center distance. That's how I found the proper gears for my shaper.

berga · Apr 24, 2019

Hi wheels,

You were correct. I actually had "overtightened" the upper bevel gear, causing its mesh to be too far away from the axis of its mating gear. So essentially there was too much backlash, which is just as noisy as too little. Thanks for the tip.

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Adjusting Z-axis knee backlash (bevel gear)

berga

Aluminum

wheels17

Stainless

berga

Aluminum

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