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  • schrink fitting

    can someone explain a bit more about schrink fitting pieces in what cases can this be used? I know in others its frowned upon. I know very little about it but it seems to be capable of carrying a heavy load so why is it not used more regularily? can you schrink fit between different metals say brass and mild steel etc? Alistair
    Please excuse my typing as I have a form of parkinsons disease

  • #2
    Alistair, there may be "rules" for when to use a shrink fit...I just don't kow of them . Unlimited situations, so some judgement is needed. We use a lot of press fits & shrink fits. Some parts won't stand up to a ehavy press, or much heat, so other methods are used. Press fits are limited to maybe .0005" per inch of diameter (VERY generally!). Often though the parts can't be gotten INTO a press for assembly. Plus there is always a chance of galling , which can put a real damper on your assembly process. Shrink fits can take a heavy load, but again the parts have to be able to withstand the pressure. I worked at a place that built rock crushers. Some of the parts had .06" or more interference. As you can imagine those machines take a tremendous beating.. The place I'm at now shrinks a lot of bearings onto shafts, etc. Bearing heaters made for that purpose make the process go smooth. Hardened sleeves assembled on rolls use the same method. If your part can take 400* heat, and you have a controlled way to heat the part, a shrink fit often works well, noting that when you want to disassemble, the parts will NOT come apart without a fight. Brass and mild steel...no problem...it works for iron "tires" on wooden wheels to Shrink fits are used, but applications that require it are limited...other methods are jsut easier/cheaper,etc. Maybe not too common for the HSM due to lack of equipment, where the only resort is fire or the kitchen sove All that being said, I'm pretty impressed with Loctite®. I've made lots of extension taps where a regular tap is somehow attached into a hole in the end of the proper length piece of round stock. We used to braze the tap in...or use set screws if there was room for them. Now it's loctite for taps up to 1/2"...very quick, easy, and removeable.

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    • #3
      I've sort-of used shrink fits on a few occasions, but not very seriously. For nearly everything I do, Loctite 609 is so much easier.

      For some things though, it would be hard to do anything other than a shrink fit -- like the shrink links on a steam engine flywheel.
      ----------
      Try to make a living, not a killing. -- Utah Phillips
      Don't believe everything you know. -- Bumper sticker
      Everybody is ignorant, only on different subjects. -- Will Rogers
      There are lots of people who mistake their imagination for their memory. - Josh Billings
      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
      Don't own anything you have to feed or paint. - Hood River Blackie

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      • #4
        Big andd little shrinks

        Alistair

        I have used shrink fits for the ring gear on an automobile flywheel as well as some tractor flywheels. To remove the ring add some heat with a rosebud torch being somewhat careful to heat the ring and not the flywheel.
        On four banger tractor engines the flywheel tends to stop the same place each time, thus the starter would always engage on the same teeth causing wear. We would heat and rotate or if really bad heat and flip so as to get "new" teeth. In this case the shrink interference was built in, so no arithmetic to do.
        I build small model flywheels from aluminum and shrink on a bronze or steel rim. In this case the load is light so I run about half a thousand per inch of diameter. heat the rim on a very flat fire brick and store the wheel in the freezer. When ready just drop the two together. The firebrick tends to keep the rim hot while I fiddle with the wheel.
        Biggest I have done is 18 inches in diameter and the smallest is about 3 inches.

        Pete

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        • #5
          Shrink fit is often used where chemicals won't hold up. One I have done is steel valve seats in an aluminum aircraft engine head. They drop right into a properly heated head, but once the temps equalize they're stuck. These are also easy to remove by heating the head and quick-cooling the seat.

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          • #6
            big-dipper, I am sure you ment to type in .006" not .06". The place I work part time builds asphalt plants and parts for them. We use a shrink fit of up to .006", most the time just .004". That is with a shaft of up to 5"dia. and the roller is a solid piece of steel as big as 26"dia x 12" or more wide. We heat the roller to a blue to straw color and then drop the shaft in the hole. We can get the holes .010"-.020" oversize but I doubt we could ever get it large enough to put a .060" oversize shaft in the hole. I don't think it would get that large if it got white hot.
            It's only ink and paper

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            • #7
              I have done quite a bit of shrink fitting of parts.

              Crank plates onto crankshafts, crank pins in crank plates. One item was a collar on a horizontal milling arbor. That one was much cheaper than turning off all the material that I would otherwise have had to.

              I have a small butane torch that I find very handy for small parts. It really doesn't take that much for a useful shrink, between heating the ring and cooling the shaft with ice or in the 'fridge freezer.. But some calculation is good to be sure you will actually have an interference when cold.... very embarassing if the parts slide apart after all that trouble!

              The arbor was tricky, since the ring had to slip 10" over the shaft and then go against a small shoulder. A little sweating as it went down..... but it worked out OK. That was a 7/8 arbor and I recall a couple thou interference was all it took, or at any rate took all teh expansion I had available without really getting it hot. (I'd have to calculate it again to be sure). That ring isn't coming off!

              Different types of metal can be shrunk, but you want to be careful if the assembly will get hot or cold. Different metals expand differently. Aluminum may expand right off a shaft, for instance, if hot enough.....
              1601

              Keep eye on ball.
              Hashim Khan

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              • #8
                Carld, these parts were pretty big 2, 3, 4 or more feet in diameter. The 1/16" shrink would be about the same as .006 on a 5" diameter. It could take the beter part of a day to finish turn the taper of the "cone" on the big lathe where ya got to ride the carraige

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                • #9
                  Thanks Guys so far good help and advice Alistair
                  Please excuse my typing as I have a form of parkinsons disease

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                  • #10
                    I use a shrink fit on the money in my wallet any time I might be near old iron.

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