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pressing small disks into rings

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  • pressing small disks into rings

    Ok not exactly.

    I have these old model train kits, 1:120 or TT sclae. Models of the Baltimore and Ohio 0-4-0t Docksider.

    The wheels components were supplied (to me) unassembled. There's 2 axles, (steel) 1 brass gear, 2 zinc/zamac spoked centers, and 2 rims/tires of unknown material (they could be nickel silver, but possibly also zinc). All these need to be pressed together. Gear on 1 axle, axles on centers, centers into rims. I had thought the best way to press the centers into the rims was to freeze the centers and heat the tires in the toaster oven, then slip them together (I forgot to mention that on 1 side of the locomotive the rims need to be insulated from the center (hub), and small strips of something are supplied. The rims that take the strips seem to be machined oversize). Well maybe I didn't heat the rims hot enough, arounf 200 degrees for about 10 minutes. There didn't seem to be any expansion or contraction. Did I do something wrong?

    I suppose I could just press them on with my horrible Harbor Fright arbor press, but I'm chicken. I'd rather try to apply my earlier method, as I've heard it's supposed to work.

    Somebody help me.

  • #2
    200 degrees may not be enough. I think you can safely go up to 350 or so. Make sure there isn't any flashing or molding ridges getting in the way.

    Small parts will tend to adopt the temperature of the environment very quickly, so work fast.

    The parts could well be of the wrong sizes to be fitted together according to plan. This might be a good opportunity to get some experience in precision measuring with a caliper or micrometer. There is a class of fit that's appropriate according to the diameters of the parts, and the smaller the parts the closer the sizes must be for the proper press fit or heat shrink fit.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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    • #3
      +1 on what Darryl said.
      Rough rule of thumb for press/shrink fit is .001" of interference per inch of diameter.

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      • #4
        +2 on what Darryl said...
        Small parts will tend to adopt the temperature of the environment very quickly, so work fast.

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        • #5
          Originally posted by Hopper View Post
          +1 on what Darryl said.
          Rough rule of thumb for press/shrink fit is .001" of interference per inch of diameter.
          The "disk" would need to be .001" larger then the rims inner diameter, per inch of diameter, or .001" lower?

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          • #6
            The ID of the outer part would be smaller than the OD of the inner part.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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            • #7
              I guess that makes sense. Because as your diameters got larger, at some point you'd have some gap there. Maybe enough to swim through.

              Thanks though.

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