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Originally Posted by dlavery
So your idea of "if I took a spur gear and (analogously) put in in a bucket of plaster, and then the plaster hardened and I pulled the spur gear out, would I have an internal gear of correct dimension/shape?" is theoretically correct. In actual fabrication, the addendum of the internal tooth is slightly shortened to prevent interference and reduce the need for undercutting on small pinions.
-dave
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Thanks dave. After six weeks of hard thinking, my brain is too tired to understand the first paragraph of your post, but I am almost understanding this part. I have a couple more questions about the theoretical vs. actual profile. Specifically, how critical is the shortening of the addendum of the internal tooth?
Say I have a large sheet of steel, say 1/4" thick. I put this sheet in a theoretical machine (like a wire EDM, or a watrerjet, or a laser) that can cut with absolutely no radius whatsoever. I cut the profile of a standard (external) involute gear. Remember, this fancy theoretical machine has no dimension whatsoever to the cutting tool (laser, water, etc.)
If I took small piece that falls out of the sheet when done, I would most definitely have a nice external gear.
Now here's my question, if I discarded this small piece that falls out, would the sheet have a nice internal gear ? If so, would this internal gear be suitable for use in something like a small planetary, not unlike the AndyMark?
Would the gears eventually "wear in" or would they not mesh at all to begin with?
If this procedure would work on this fancy theoretical machine, would it work on an actual machine?
Thanks for your help.