HP 46/81 idler gear

[Duane Hess]

Reviewed various posts in the archive. Sure I didn't see all of them.

You are correct the gear is modulo 0.4 and 68/17 teeth. Don't know about the pressure angle, but any gears you order (I've fabricated several from individual gears) always seem to be 20 degrees. Circular pitch means nothing to me. Know nothing from gears, but I take it module and teeth count defines all kinds of stuff, like total outside circular diameter, some diameter near bottom of teeth (reference) (circular pitch?), circular pitch, diametrical pitch and a whole bunch of terms I have absolutely no understanding of.

Put used gears under a USB microscope I have, angles of the thrust surface vary greatly from 23-28 degrees. I assume that's wear, as the edges were always rounded. I don't know beans about gears, but any Google research I've done on all kinds of old 70's products, 20 degree thrust angles seems to be a standard.

You know, it never dawned on me until now why I haven't tried viewing gears from devices I know that have had little use. i.e. a Canon unit I purchased new and other stuff. Guess I'm dumb.

The teeth face width and hub width are the same. The overall thickness of the gear is 7mm. Thickness of the 68 teeth gear is 3mm. As you can guess the thickness of the 17 tooth gear extends 4mm from the side of the 68 toother.

The bore is 3.0mm. I've fabricated a number of gears, all were 3.0mm; fit well, no wobble and no binding. 3mm corresponds with posts/notes I've had with other users. There was a 3.0mm bore fluted brass ferrule which took a 3.2 bore gear. But that ferrule doesn't seem to be available anymore. It was quite handy.