How to make gears mesh properly.

[Andy Baker]

Good question. Keeping tight tolerances on center-distance spacing when designing gearboxes is a good thing to do. In your case, it is OK to specify 1.500" distance if the fabricator keeps a tolerance of +/- 0.001".

Another way to dimension it would be to call out 4 places, at 1.5000". Traditionally, the tolerance for this dimension would be +/- 0.0005".

I know that there are other engineers who say to add 0.002-0.003" to the center distance. That will work also, as it is a more conservative way to design. It will add a bit of backlash (not sure how much).

It really depends on the level of quality and tolerance your fabricator can handle. If they are very good, go with a four-place tolerance. If they are just OK, then add a few thousanths for backlash.

Good luck,
Andy B.