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  • drill rod question

    When the drawing for model engine ask for drill rod. It is as it come or it had to be hardened. The wrist pin for example.

  • #2
    Small model engine?... I would say unhardened as your running low horsepower.
    Many wrist pins are hollow... if you stay with a solid one I would think you would be ok
    Walt

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    • #3
      Generally, a wrist pin is hardened, even on a model engine. Often, the size is such that a standard dowel pin can be used, and those are already hardened and "on size". They can be cut with an abrasive wheel; try to keep the uncut end cool while cutting.

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      • #4
        I would agree with jdunmyer. If drawings call for drill rod I would take it as I'm supposed to machine it out of a tool steel that can be hardened.....unless it was a something like instructables in which case i'd take it as needing something sort of round an shiny

        dowel pins are perfect for things like that
        in Toronto Ontario - where are you?

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        • #5
          If the wrist pin has a roller bearing on it, then hardening is an absolute must, if it's a bearing surface, such as a bushing or just aluminum or brass con rod, you would still benefit from hardening and having a high polish.

          I have rebuilt/repaired a lot of modern model airplane engines, both glow and gasoline, once the engines get down to a small enough size they are too small to have needle bearings on the crank and wrist pins, then they have bushings and require 15-20% lubrication.

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          • #6
            Was reminded of this thread today while working up the drawings on Doug Kelley's latest engine. He calls out drill rod in a number of places, though none of it needs to be hardened for this build. Most items in our construction articles represent what the author used, but there are often other choices that can be made.

            In the case of drill rod, many guys have a stock of it on hand and the size is consistent enough to use it as-is, so it tends to get called out a lot. If you feel the part should be hard, harden it, but be aware that when it says drill rod, it doesn't always mean it needs hardening.
            George
            Traverse City, MI

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            • #7
              Unhardened aka anealed drill rod is almost the same as 1020 steel. So why even go to the trouble to request it's use? Once hardened and tempered it's FAR superior.

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              • #8
                Another easily obtained quality material that most likely could be substituted would be a grade 8 screw. Except that is already hardened and tempered thus machining may be more difficult.

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                • #9
                  Grade 8 screws and bolts machine fairly well, especially with carbide. Usually the shanks are undersized, as most of them are made by thread rolling.
                  Kansas City area

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