Pinion gear; take 4; no juice

October 22nd, 2008 § 2 comments

I attempted to cut a pinion gear again, with no luck.

I’m using a 24 pitch 14.5o involute gear cutter on a Sherline gear cutting arbor. I want to cut a 12 tooth gear. I turn a 3/4″ round bar stock down to 37/64.

(Teeth + 2) / pitch = Outer Diameter
(12 + 2) / 24 = .5833 ~ 37/64

I then transfer the chuck to the rotary table. I lower the headstock so that the bottom of the gear cutter touches the blank. I then divide the cutter height by 2, and lower the headstock by that much:
Cutter width = 15/64, half = 1/8.

The radius of the blank is 19/64.

And somewhere I’m off by a 1/64 of an inch which blows the tooth geometry…

I much be sloppy somewhere and am just missing it.

§ 2 Responses to Pinion gear; take 4; no juice"

  • Enrique says:

    You use Teeth + 2 to get the outer diameter, do you want the outer diameter, the middle diameter or the inner diameter?

    You probably know what you want, I’m just using the Socratic method to help you find the answer:)

  • Louie says:

    Hello Enrique,
    The pitch calculated by the halfway point on the tooth. So a 24 pitch gear with 24 teeth will be 1 inch at its pitch diameter. In order to get the outer diameter, add two to the teeth.

    What I was missing was that I’m using a 14.5 degree gear tooth cutter. Turns out this pressure angle is out dated in favor of a 20 degree pressure angle. The reason – cutting pinions. After working on this a bit, it looks like the I was hitting two problems: 1) Center was off; I corrected this by finding the center on the lathe then transferring to the mill and lining up to the center point. Works within .001″. 2) With the pinion the depth of cut doesn’t include clearance, so you calculate the depth of the cut using the addendum and deddendum. I now have a usable pinion gear (not perfect, but usable)

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