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Shrinking bores with heat

Discussion in 'Shop Talk' started by skyking1, Nov 28, 2020.

  1. John C.

    John C. Senior Member

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    The collar is to keep the pin from turning in the boss. It usually doesn’t touch the OD of the pin. Heating the boss will make the steel expand making the hole in the center get bigger, not smaller. The steel used for the house frame has been mild steel in all my experiences. I’ve never seen bushings work in a boom foot. They usually crack and break in pieces when someone starts to impact load the boom.
     
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  2. Theweldor

    Theweldor Senior Member

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    The general rule of thumb is to have as much support at the bosses to equal the diameter of the pin. So if you have a 3" pin you should have 3" of support for it at each end. "From a machinists point of view" The lovely engineers always try to cheat that a bit.
    They are keeping tracked of cost. Those two machines the way I did them the boss when cooled shrunk onto the pins.
    However you are correct that boss with the bolt its only purpose is to keep the pin from spinning.
     
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  3. skyking1

    skyking1 Senior Member

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    fingers crossed. I have a couple of pairs of bushings waiting for this to come apart. I'd tear into it now, but I *might* need it on the next job, a really muddy mess where it might be handy to reach bedding in to the mini.
     
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  4. Theweldor

    Theweldor Senior Member

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    I know how that goes. You can't always fix it at the most optimum time. Everybody has to have a hamburger.
     
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  5. skyking1

    skyking1 Senior Member

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    I confirmed with a second manager at a different Pape equipment facility on the heating thing. He said it was good for a maximum of .020~.025
    No quenching, not a ton of heat. We'll see if I even get to try it, when the new pin comes in.
     
  6. ETER

    ETER Well-Known Member

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  7. ETER

    ETER Well-Known Member

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    Just did some stick, bucket pin and bush work on a 490D a couple of weeks ago for a fella and we measured .068" vertically between the boom and house... since it is a low use machine, we will measure it again in a year or so and see what the indicator reads.
    If it is significantly worse, we will weld, bore, repin and bush then.
    Regards, Bob
     
  8. ETER

    ETER Well-Known Member

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    Also, meant to add above that I agree with most said regarding the pin bosses and such... not so sure a .020-.025 bore reduction is achievable regardless of technique/method by heating.
    Regards, Bob
     
  9. Jonas302

    Jonas302 Senior Member

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  10. skyking1

    skyking1 Senior Member

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    I'll set up some tooling to measure it if i try it.
     
  11. bigrich954rr

    bigrich954rr Well-Known Member

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    yea that's the bolt i used one at work seems to be doing good
     
  12. terex herder

    terex herder Senior Member

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    Heating will work, if done properly. To put a fine point on it, you are using heat to cause localized upsetting. Its a similar process to welding distortion.

    What happens is you heat a small section of metal. The metal wants to expand, but it can't because it is restrained by the cold metal surrounding it. But the forces of expansion are stronger than the strength of the metal, so the metal compresses itself. Now when the metal cools, it pulls the surrounding metal in, making the bore smaller or a beam bend.

    Lincoln Welding has many old videos on Utube. One on welding distortion illustrated this by putting a steel bar endwise in a vise. Tighten the vise so it holds the bar. Now heat the bar in the middle. When the bar cools, it will fall out of the vise.

    If you wish to know more about the subject, look up flame straightening.
     
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  13. Tugger2

    Tugger2 Senior Member

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    I have done a fair bit of repair on bores like that over the years. As said above theres no fix like building up and boring .Machine frames are generally mild steel/50000yield material so they accept buildup well . Pin bosses like that are always out of round once you measure them properly. In my days of line boring we always built up by hand . Now days with a bore welder its pretty quick with the right guy on it. If your going with a new pin id be line boring while its apart. We made a lot of pins ,mainly stick to bucket when built thumbs as OEM didnt supply long enough pins. 4340HTSR and then induction hardened always worked well. Always used OEM bushings wherever possible , or Torrington bearing races where we couldnt size a bushing.
    Any shrink fix you might accomplish will work loose pretty quick and maybe be worse.
     
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