Hole size after heat treat?
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    Default Hole size after heat treat?

    Press fitting a 0.200" pin in some S7 parts.

    Will the hole close or open during heat treat? During tempering specs says the material grows 0.1%. I've searched the forum and elsewhere and both answers are given.

    What say ye?

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    I would plan for the hole to grow in size.

    Probably use a .1985/.199 reamer, Checking for fitment with a gage pin in a test piece.

    Then, hone the holes with a split lap post H.T.

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    Quote Originally Posted by Thunderjet View Post
    I would plan for the hole to grow in size.

    Probably use a .1985/.199 reamer, Checking for fitment with a gage pin in a test piece.

    Then, hone the holes with a split lap post H.T.


    See post 11: 4140 heat treat hole shrinkage

    I would think the hole would grow also, are these guys wrong? They seem pretty sure that it shrinks.

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    My experience is that holes with lots of meat around, always shrink...
    What's your application Terry? If the holes do grow, can you retain pins with Loctite 603 or does it have to be a press fit?

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    Quote Originally Posted by barbter View Post
    My experience is that holes with lots of meat around, always shrink...
    What's your application Terry? If the holes do grow, can you retain pins with Loctite 603 or does it have to be a press fit?
    It's for a small U-joint, major diameter is 0.375". Need a good press, 1/2 thou or so, had a pin spit out with only a couple tenths press.











    One vote for grow, one for shrink...

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    There are heat treatment charts that show material size change for various alloys. the movement depends upon the tempering temperature.

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    Do a test piece.

    Use Loctite green with primer.

    That small cross section will not tolerate much of a press fit, I'm not surprised that you broke one.

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    Leave it small and carbide ream after ht ?

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    Quote Originally Posted by Steven-Canada View Post
    Leave it small and carbide ream after ht ?

    Not a bad idea, but even reaming isn't that "close".

    Was hoping to hit the hole size pretty close to 0.200" after heat treat and have minimal lapping to get to size.

    I can check the hole with pin gauges and then finish the pin to + 1/2 thou checking with a tenths mic.

    But to make the hole big or small initially? Or just make it a thou or so small only to have it close up more and have a helva lot of lapping to do (and it's inherent issues ie: barrel/hourglass shape etc.)
    Last edited by Terry Keeley; 10-05-2020 at 10:33 AM.

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    Quote Originally Posted by Terry Keeley View Post
    Press fitting a 0.200" pin in some S7 parts.

    Will the hole close or open during heat treat? During tempering specs says the material grows 0.1%. I've searched the forum and elsewhere and both answers are given.

    What say ye?
    The answer is yes. It will grow or shrink...depending. Several factors here.

    Focusing on just the hole, think about its circumference. The material grows during quench and that means the circumference gets larger hence the hole gets bigger. Works every time if the material around it also grows.

    Since the entire part never quenches exactly at the same microsecond, some places will quench sooner, think solidify, before other sections make the same transformation. Bad thing and good things can happen because of this.

    Now go back to thinking about the hole. Suppose everything around it quenches first. Now comes the hole’s turn. The physics of the microstructure transformation forces the material to grow. It just has to. It can’t grow outward as everything around it is already solid. Only one place left. Grow into the hole. The hole gets smaller.
    So it can grow and get smaller...depending

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    Quote Originally Posted by Terry Keeley View Post
    Press fitting a 0.200" pin in some S7 parts.

    Will the hole close or open during heat treat? During tempering specs says the material grows 0.1%. I've searched the forum and elsewhere and both answers are given.

    What say ye?
    Volume increases very slightly, if everything (HT) was good you'd likely not measure any difference in a small hole somewhere. The 1% bulge# is incorrect for S-7, Bethlehem & Carpenter pin the growth at .001” and .0005” respectively per inch of section using exactly the same chemistry. Vasco also had a (quallied) 5 alloy S-7 that's similar and is silent about any change in size (docs).

    Attaching Carpenter, and will try to attach Bethlehem in another post with larger pic sizes… The first page shows size change by temper graph and the stuff actually shrinks at the right temper range.

    Good luck,
    Matt
    Attached Thumbnails Attached Thumbnails carpenter_s7a.jpg   carpenter_s7b.jpg   carpenter_s7c.jpg   carpenter_s7d.jpg  

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    Quote Originally Posted by Matt_Maguire View Post
    Attaching Carpenter, and will try to attach Bethlehem in another post with larger pic sizes… The first page shows size change by temper graph and the stuff actually shrinks at the right temper range.
    Now gonna try attaching Bethlehem in larger size 'cause you can't make sense of them at 100kbits.
    Attached Thumbnails Attached Thumbnails bethlehembearcat_s7a.jpg   bethlehembearcat_s7b.jpg   bethlehembearcat_s7c.jpg   bethlehembearcat_s7d.jpg  

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    The material grows in all directions in heat treat in my experience. This means holes get smaller and outside get bigger. I have seen holes get larger so no 100% rule.
    Test parts are the only way to know and the heat run of the stock certainly changes this compensation.
    If you make lots of parts stock heat runs are kept separate due to this problem. New batch and things work differently.
    Bob

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    Thanks for the info Matt, the 0.1% I quoted was from Interlloy: http://www.interlloy.com.au/our-prod...el/?output=pdf

    Latrobe says it should be less tho at the 400F tempering temperature I'm using: https://fordtoolsteels.com/wp-conten.../10/LSS_S7.pdf

    My toolmaker buddy also says the hole will shrink slightly, although we're talking tenths here. I bored the hole to a tight fit on a 0.200" - gauge pin so we'll see tomorrow where it ends up.

    Got to use my new Wohlhaupter boring head tonight, what a treat after years with the Criterion!
    Last edited by Terry Keeley; 10-05-2020 at 09:50 AM.

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    so to summarize: if overheated before quenching it will shrink. depending on tempering temp. it will first shink and then grow. yes?

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    Quote Originally Posted by Terry Keeley View Post
    See post 11: 4140 heat treat hole shrinkage

    I would think the hole would grow also, are these guys wrong? They seem pretty sure that it shrinks.
    imo, 4140 heat treating is a crap shoot. S7 (most tool steels I think) should be much more stable, but been out of heat treating for a long time now. Have access to a hone? Should be easy enough to lap/hone a thou or so. Or loctite or bearing seal of some sorts if it opens up.

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    Sounds like you need a Sunnen hone. They aren't too expensive used. It won't take long to do the part. And you will enjoy the Sunnen for the rest of your life.

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    Hi Terry:
    The consensus is you don't know and can't know...no matter what you do there are potential confounding variables and you don't know which way they will fall for each part in each batch.
    The only safe way forward sadly, is to make the hole undersize and then hard mill it, bore it, ream it, wire it, jig grind it, lap it...whatever you have to do to get your tenths sized hole after HT.
    All must accept this reality or take a chance on having to scrap some.

    It's a simple part, and scrapping some is a perfectly viable plan if that is your least troublesome way forward.
    So make a few, bore the holes to various sizes, harden them and see which one gives you the best outcome.
    Make them all like the best one, knowing you'll pitch a few or have to rework a few or both.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Quote Originally Posted by implmex View Post
    So make a few, bore the holes to various sizes, harden them and see which one gives you the best outcome.
    Unfortunately, that doesn't always work.

    8620 is very predictable. I once did a fairly large batch of parts, all the same material, same batch of steel, all machined at once, didn't need them all at the same time for assembly so sent them to heat treat in two groups. First group the bores shrank as they are supposed to, second group the damn bores grew several thousandths. Bores in 8620 never grow, but they managed to do it.

    The only truly reliable way is to make them small then hone to size.

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    Good morning Emanuel:
    The point I was trying to make concurs exactly with the one you just reinforced...You DON'T know. you CAN'T know but you have to take a chance and pick a strategy.
    The choices are:
    1) Be safe and make them deliberately undersize and do a second operation OR...
    2) Make some in a range of sizes, pick the best one, make them all like that and PRAY, knowing you will likely have to pitch a few and lap a few.

    Your risk tolerance determines which option you pick
    We are actually in full agreement here.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining


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