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Thread: Heat Treat Distortion 8620

  1. #1
    Join Date
    Sep 2004

    Default Heat Treat Distortion 8620

    I am making a Hypoid gear set. I have the teeth cut at a Gear Shop (not too many could even do them) Now the pinion shaft is 1.680 diameter . I was thinking leave it oversize .020 for heat treat distortion and finish turn dia with a ? cermet insert or whatever after heat treat. This shaft also has a thread on it. I was going to cut the thread to size and then finish turn bearing shaft diameters afterwards,. What you think guys is this proper way to do this ? I made the mistake of finish boring the inside bore knob on of the two gear blanks (8 inch diameter) prior to heat treating. I will have to see if the inside bore is oval or out of round grew or shrunk (i hope shrunk) and then either its OK or i will have to machine oversize to clean up and get hard chromed and ground. Thought this post might help others know bout perhaps leaving .020 on inside bores of heat treated parts so you can machine to size after the heat Treaters done with them. I wish i had of known Thanx Mike

  2. #2
    Join Date
    Dec 2004
    where the Snake swallows the Salmon


    I've never worked with 8620, but I used to make a few small dies with drill rod. The critical ID's ALWAYS shrank after heat treating. Furthermore, they might continue to shrink over a period of days.

    I dealt with the shrinkage by honing the ID.

    I still make many small bushings out of drill rod. The OD shrinks 0.0005" - 0.001" on a 1/4" bushing, however, it's not critical for that application.

    Not sure how I would handle your part. Can 8620 be machined with normal tooling after heat treating ? Or is grinding required ?

  3. #3
    Join Date
    Jan 2003
    On the Oil Coast,USA


    Your good on the oversize,should be able to finish machine the 8620 after heat treat and draw down.

    The bores,well they will shrink,but most likely the volumetric shrinkage will offset it.Worst case would be an egg shaped bore which is possible.
    I just need one more tool,just one!

  4. #4
    Join Date
    Jan 2010
    somewhere in downstate chicago-tax-us-to-death

    Default moving 8620!

    I have a bearing race of 8620 which is heat treated to 60-62 Rc. It needs to be line lapped and is undersized by .003". I have not been able to even mark the surface so far. Am told my lap pressure is not high enough. Point is, this material is hard to move after HT. So I think would need cermet or exotic tooling to work after HT. I will see this aft-noon whether or not I can move .003" out of the bore.

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