setting backlash on your gear drive

This post was originally created by a user who rage quit and took his toys home with him. However, I find the information very useful and I think you will too, so I’ve restored it into a new thread. No regrets.


A member suggested I should create a thread for setting up backlash on gear drive so here goes.

Setting backlash in and of itself is a dubious term.

  • j is the backlash distance from a drawing perspective.
  • from an engineering perspective, the backlash is defined by the tooth profile and cannot be changed, ie j=backlash distance when points of pressure are in alignment.

Basically, the term ‘adjust your backlash’, is saying the center to center distance is incorrect and the points of pressure are out of alignment. Changing center to center distance doesn’t actually change the engineered backlash of the tooth profile. But it does change the “effective backlash distance” but not the engineered distance.

So adjust the center to center distance, so that the points of pressure align, do this by eye. Paper works, but is pretty imprecise and I do not suggest that method.

  • point of pressure is where ‘face’ and ‘flank’ meet at the ‘pitch point’ or ‘pitch circle’ … yes that tiny line not the face.


  • note the ‘pressure angle’ and ‘line of action’, see how the line passes through the ‘pitch point’, to the ‘bottom land’ of the opposite side of the tooth?

this angle provides the thickest support structure, any mis alignment weakens it

  • too close of center to center lowers the pressure angle and raises the line of action above the base of the bottom land, teeth break off
  • too great of center to center, will wear teeth and sharpen them. The the pressure angle is to great, and the line of action is actually scraping the teeth with each pass vs pushing

Excellent resource! It’s always hard to explain to people who don’t know much about gears

Now I have something to forward


You’ll be hearing from my lol’yers


Damon, Thank you for bringing this back.


Yeah as much of a manchild as he turned out to be, the departure of a lot of his posts was a major loss.

If you’re reading this @deckoz :fu::fu::fu::fu::fu:


maybe there’s something I can do about some of his other… um… fingered posts.

There was many :cry: before the breakdown he was one of the more helpful folk around. I was sad to see a lot of his posts disappear.

Bring them all back!

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I think it’s worth the effort. I’ll see what I can do.

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shaft of motors aren’t perfectly straight so its almost impossible to ajust perfectly , if i turn my motor i can feel a small play but if rotate fews degree i become tight a little , so i leave it like that, and see what gonna happen after the break-in

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I’d put that down to the gears themselves rather than the shafts.

I’ve never fitted a gear drive that was perfectly concentric. I always just adjust the backlash to the tightest point