"Harold & Susan Vordos" wrote in message
...

"Terry Coombs" wrote in message
...

I just got to wondering about internal stresses in 4140 round stock .
I'm making a part for an oilless compressor , and have it roughed a bit
oversize . I know that some steels and other metals develop internal
stress from forming operations , and need a few hours to let the stresses
equalize before finishing machining so the finished part doesn't distort
. Got to wondering if 4140 is one of them .
--
Snag


It is generally accepted that all parts have stress, the result of the
manufacturing procedure, as you alluded. Hot rolled materials tend to
have much less.

Good shop practice dictates that one roughs parts, leaving sufficient
material for finish machining, with total cleanup. The less material
remaining, the better, as the piece will more closely represent the
finished object, and the small amount of material removed in the process
should make very little difference in movement of the part. I expect
that unless you have a very critical dimension, less than .0002"
tolerance, you should be fine.

Nice job. I spend a lot of my time trying to have folks understand that
roughing is a very important part of machining. Some don't pay attention
(until they have the pleasure of reviewing the resulting scrap, anyway).

Time can be a factor, but the roughing should release much of the stress.
If you have doubts, allow the part to age a day.

Harold

I backed off the chuck jaws a tad before I came in , rechucked it after a
couple of hours . After recentering it I found about .002 runout on the last
area I'd machined same setup . Looks like it might have had a bit of
stress . I'll finish it up today .
--
Snag