Posted by BillS on September 26, 2009 at 09:45:55:
In Reply to: Re: barber colman #12 gear hobber questions posted by Jim Pollock on September 24, 2009 at 21:23:25:
There is always some distortion in dimensions after heat treating, whether due to relieving stresses due to machining/work hardening, or carburizing. Sometimes the bore expands when it is a large bore, and shrinks when it is a small bore.
I gotta say that .018 is a lot, but may be that large due to being 62Rc and .030 deep. Back in the old days, we would carburize .010-.020 deep and 60Rc max. And I would think that OD growth is proportional to size.
There are many folks here that are knowledgeable in heat treatment and distortion of the kind you are seeing
( the "Surface damage on hard cut gears" thread below is an interesting example).
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