oversize tapped holes for heat treat
Posted 03 July 2012 - 06:25 AM
Posted 03 July 2012 - 07:49 AM
finish dowel holes after HT especially if location needs to be held.
Posted 03 July 2012 - 07:59 AM
How the parts are heat treated will effect this to a point but here is a common rule;
A2 will move .0002/in in heat treat. S7 will be close to that. S7 does not move as much in heat treat.
For dowel pin holes, a .0002 U/S is a press fit. A 3/8" dowel pin is .3752". I run a .3752 to a .3755 reamer before heat treat. Dowels are still tight in that range, but not too tight.
For small thin parts stay on the tighter side.
Also it helps if you are doing this day after day to keep some barrel hones and lapping compound in the shop just in case.
Tapping, I just use a a loose tolerance tap. Don't use a tight tolerance tap, or a worn out one. You can go to a .001 O/S tap if the holes are deep. That helps a lot but not always needed.
Posted 03 July 2012 - 08:10 AM
I prefer a much more controllable situation, O/S taps, final size and location after HT
Posted 03 July 2012 - 05:40 PM
Anyone else notice that much movement or did my heat treat place suck? It was a place called special research in madison heights michigan, bet it isn't there still.
Posted 04 July 2012 - 06:56 AM
I've had about the same results in A2.. it doesn't move a whole lot in heat treat.