Posted by BillS on March 30, 2015 at 16:16:25:
In Reply to: Re: Flat spot when hobbing spur gears posted by Dimebag on March 30, 2015 at 04:25:02:
Does it seem to happen for about half of the setups, or for all setups?
Is it more pronounced for small number of teeth (as you said for pinions), but not in all setups?
Is the flat spot on the same tooth flank always, or does it appear to move from one flank to the other from one setup to another?
I'm wondering if centering a hob tooth to centerline of workpiece might have an affect. If yes, then the flat would remain in position on tooth flank as hob table moves.
We tend to look at hob as continuously generating the tooth, which can a good assumption when many hob teeth enter and exit the tooth space. But for small number of teeth and a coarse pitch hob with only a few gashes, maybe this is not a continuously generating process.
Also the tooth chip is is removed as the workpiece rotates through a small but discrete angle.
Anyway, I'm trying to visualize how a hob tooth could make different tooth flank features as it rolls into and then out of a tooth space, and possibly could be more symmetrical if a hob tooth is perfectly centered on a tooth space at full depth of cut?
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