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Re: [hobbicast] Shrinkage

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  • greg_taylor@pullmanind.com
    sentto-1941855-220-962805669-greg_taylor=pullmanind.com@RETURNS.ONELIST.COM on 07/05/2000 10:04:05 AM Please respond to hobbicast@egroups.com To:
    Message 1 of 8 , Jul 5, 2000
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      sentto-1941855-220-962805669-greg_taylor=pullmanind.com@...
      on 07/05/2000 10:04:05 AM

      Please respond to hobbicast@egroups.com

      To: <hobbicast@egroups.com>
      cc:

      Subject: Re: [hobbicast] Shrinkage


      First, here's what the books say regarding shrinkage: Aluminum small
      castings 5/32" per foot and 1/8" per foot for large castings. The reason
      for the difference is that you pour large/thick castings at lower
      temperatures. With less heat in the melt, you have less expansion of the
      metal and therefore less shrinkage in the casting. Brasses and bronzes
      shrink 3/16" per foot.

      Now, since you like me, probably don't have an expensive shrink rule, try
      my
      method using decimal fractions rather than common fractions. (3/16) .1875"
      divided by (1') 12" =s .015xx. For example, the length of your casting is
      to be 7 1/2". Multiply 7.5 x .015 and add the result to 7.5 to get the
      length of your pattern. 7.5 + .113 =s 7.6125". Round off to something you
      can read on your decimal rule and you are ready to make your pattern.

      You may want to provide a bit for finish work. I use .02 for shrinkage if
      I'm going to do some light sanding and polishing. And I use .03 for a bit
      of machining.

      Best, Jerry

      PS I've been off line for several weeks--fell off the roof, and dinged my
      back. It still hurts some but getting better.


      Custom Castings by Twaddell
      foundryman@...
      http://members.igateway.net/~jtwad/



      Hi Jerry,
      Thank you for posting this more-detailed information for the group to
      "digest." I believe that I am understanding all you're saying now! As for
      the valve covers I emailed you about casting for me, I would actually have
      to make my pattern 22.22" long to obtain a final 22.00" with the
      0.125"/12.00" shrinkage factor for the large casting ?! I am assuming that
      these valve covers would be considered a LARGE casting due to their final
      size of 22.00X5.00X3.50X0.25thick ... am I correct, or would this still be
      a SMALL casting?

      Thanks in advance! Thanks for the help!

      Sincerely,
      Greg Taylor :)
      Editor Guy/Web Master - Great Lakes Classic AMC Club
      http://www.turboforce.com - AMC & Stude Turbo Racing
      http://www.turboboost.com - AMC Turbo Power
      http://members.xoom.com/glcac - Great Lakes Classic AMC Club
    • Buchanan, James (Jim)
      All: I normally design my part and patterns using Autocad. I scale the part using the shrinkage factor. Then I print the part using a laser printer at 1 to
      Message 2 of 8 , Jul 5, 2000
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        All:

        I normally design my part and patterns using Autocad. I scale the part
        using the shrinkage factor. Then I print the part using a laser printer
        at 1 to 1. I either glue the print out to the wood pattern material and
        proceed to cut it out. In some cases I use a divider to pick dimensions
        from the full size prints and transfer them to the pattern. A good
        laser printer should be within 1/300" (0.0033") and that's close enough
        for what I do.

        --
        James Buchanan
        Lexington, Kentucky (The Blue Grass State) USA
        Two Truck Climax Locomotive Operator & Builder
      • Foundryman
        Great on you guys!! Good posts on shrinkage--way beyond my simplistic approach to shrinkage. A shrink rule would be the easy way to go if they didn t cost so
        Message 3 of 8 , Jul 5, 2000
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          Great on you guys!! Good posts on shrinkage--way beyond my simplistic
          approach to shrinkage. A shrink rule would be the easy way to go if they
          didn't cost so much for my limited use. I want one! After rereading my
          post, I realize that I didn't mention the expansion for rapping out the
          pattern. As most of my patterns have plenty of draft, 5 degrees, I seldom
          have to rap to remove the pattern, but a great reminder for me and all.
          Also, I didn't mention my method for grinding a pattern's draft to square or
          whatever. As most of my patternwork is decorative, I use the TLAR
          method--that looks about right!
          Great comments to my post and thanks as I've learned from them.

          Best, Jerry


          Custom Castings by Twaddell

          foundryman@...

          http://members.igateway.net/~jtwad/
        • DTollenaar@AOL.COM
          Jerry, Was it the fall, or the sudden stop with Terra Ferma that caustd your discomfort. Thanks for the info on Aluminum shrinkage. I ve been told to figure
          Message 4 of 8 , Jul 5, 2000
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            Jerry,

            Was it the fall, or the sudden stop with Terra Ferma that caustd your
            discomfort. Thanks for the info on Aluminum shrinkage. I've been told to
            figure .125 to the foot before, so this confirm's it. Most of the casting I
            will do will be Model Engine crankcases, back plates, cylinder head's, etc.
            These are in the range of 1.5" wide by 3" tall and long. I'll plan on
            .030/.050 max. over size for the pattern. May even back off to .010/.015 for
            really small parts. Next comes the question of the pour temprature. I have
            an electronic theromo. intended for heat treating that has a range to 2500
            deg. F. I guess it could be used. The probe is about 12 to 18 inches long,
            so could be hand held if I ware asbestous gloves. I know, they are a health
            haz., but I had them in the USAF many years ago, before all the OSHA BS.
            According to the Gov., we cant do anything without risk. Oh well, life is a
            B_ _ _ _ _, and then you die.

            Thanks for the info, and please get well soon, I cant wait for you to
            complete the book.

            Dirk T.
          • Ronald Thibault
            ... Jerry; My sympathies on your fall. I m just about to get off crutches myself, after falling off my roof and breaking a hip, about 2 1/2 months ago. Ron
            Message 5 of 8 , Jul 7, 2000
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              At 09:04 AM 7/5/00 -0500, you wrote:
              >PS I've been off line for several weeks--fell off the roof, and dinged my
              >back. It still hurts some but getting better.

              Jerry;
              My sympathies on your fall. I'm just about to get off crutches
              myself, after falling off my roof and breaking a hip, about 2 1/2 months ago.

              Ron Thibault
              North Augusta, SC USA
              Builder Miinie #2
              Captain R/C Combat Ship USS Arizona
              http://pages.prodigy.net/thibaultr/
            • Ronald Thibault
              ... Most of the newer Injets will also print to this resolution. I have an old wide carriage dot matrix printer that also has this good a resolution. I use
              Message 6 of 8 , Jul 7, 2000
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                At 04:19 PM 7/5/00 -0400, you wrote:
                >All:
                >
                >I normally design my part and patterns using Autocad. I scale the part
                >using the shrinkage factor. Then I print the part using a laser printer
                >at 1 to 1. I either glue the print out to the wood pattern material and
                >proceed to cut it out. In some cases I use a divider to pick dimensions
                >from the full size prints and transfer them to the pattern. A good
                >laser printer should be within 1/300" (0.0033") and that's close enough
                >for what I do.

                Most of the newer Injets will also print to this resolution. I
                have an old wide carriage dot matrix printer that also has this good a
                resolution. I use it for printing drawings that are too big for the injet
                printer (~ 12" wide by as long as the fan fold paper is).


                Ron Thibault
                North Augusta, SC USA
                Builder Miinie #2
                Captain R/C Combat Ship USS Arizona
                http://pages.prodigy.net/thibaultr/
              • Foundryman
                Ron, What is this about military types falling off roofs? I m a retired USAF pilot. My back problems started in 75 when I crash landed a T-Bird on Maui.
                Message 7 of 8 , Jul 7, 2000
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                  Ron, What is this about military types falling off roofs? I'm a retired
                  USAF pilot. My back problems started in '75 when I crash landed a T-Bird on
                  Maui. My Dr. decided today to send me in for a bone scan to see if I have a
                  new fracture or two to add to those from the crash. Hope you are about to
                  get off your crutches and that your hip is on the mend.

                  Best, Jerry

                  Custom Castings by Twaddell

                  foundryman@...

                  http://members.igateway.net/~jtwad/
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