Posted by BillS on September 06, 2007 at 00:06:02:
In Reply to: Straight vs helical gashes on hobbing cutters posted by Dimebag on September 03, 2007 at 13:11:01:
Ya know, I've never thought about that -
It seems that, at a small lead angle, the helical gash hob would present a negative rake top angle on one flank and a positive rake top on the other side- Just looking at it from a cutting tool standpoint. If true, then the positive rake would require more cutting force? And, some have a built-in negative rake from top to bottom by the gash being ground at an angle to the ideal radial. I know that grinding at an angle to the radial changes the rack form pressure angle. Seems like the helical gash would also change PA unless the normal pressure angle is compensated when the hob is made.
Maybe someone will enlighten us about when it's best to use helical gash hobs versus straight gash?
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