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Originally Posted by sanddrag
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.
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The criticality of the reduction in the height of the addendum is dependent on the relationship between the internal gear and the pinion. If the pinion is small in relation to the internal gear (e.g. 10 tooth pinion, 60 tooth internal gear), then then reduction to the addendum can be small (but there still needs to be some). But if the gears are close in the number of teeth, then the potential for interference is significant unless the addendum is reduced. There is a specific formula for this that is based on the separation between the two base circles and the height of the addendum, but I don't remember it right now. If I can find it, I will let you know.
With regard to cutting the internal gear with your theoretical cutting machine, yes this would work. However, as this theoretical cutting machine has the ability to cut the part with a kerf of zero dimension, the resulting gear would be a perfect involute with no backlash. This may not be a desirable situation, as zero backlash setups can lead to rapid wear of the tooth surfaces.
-dave