Re: Helical gears

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Posted by BillS on November 11, 2005 at 21:38:36:

In Reply to: Re: Helical gears posted by frank on November 11, 2005 at 06:35:46:

Well, it may not be as strange as it sounds. I ran a job on a CNC lathe that did a 3 lead worm thread, which was bad about breaking carbide inserts - I had no center for outboard support.

Direction and hand of lead is everything when chasing threads on any lathe. You want to set up so that rotation and hand of thread will assure that the cutting pressure pushes the tool away from the flank being cut. The wrong combination is like climb cutting, which pulls the tool into the flank.

Ideally you would go to depth cutting only on the root and the "good" flank. But with a gear tooth profile you're going to have to cut both the "good" and the "bad" flank, where you will have to do climb cutting.

And the profile - how would you ever grind the endmill to the correct involute form? Theoretically I suppose it could be done, but...

Also, I don't think the positioning of the start of each cut (lead or tooth)is going to be accurate enough on a CNC lathe to keep the tooth-to-tooth error small. I think you would be lucky to get 1 or 2 tenths accuracy tooth-to-tooth.

Okay Frank, I'm convinced. Baaad idea.

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