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Re: Parting Dust question

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  • Gary Lekvold
    Hi Rick, Maybe I shouldn t have used the term, proper rapping , maybe I should have said, the way I was taught to do rapping . I ll give it a shot here, but
    Message 1 of 31 , Jan 5, 2008
      Hi Rick,
      Maybe I shouldn't have used the term, "proper rapping", maybe I
      should have said, the way I was taught to do rapping". I'll give it
      a shot here, but before anyone jumps all over me, this method has
      worked great for me for years, if you have a better way, than by all
      means keep doing it your way. First off, I bandsawed several
      patterns out of 1/2" and 3/4" stock for the rappers, cast them out of
      aluminum, and then cleaned them up They are about ten inches long
      with an opening at each end, very similar to an open end wrench. I
      have one that is about 1/4" opening and several more up to about 1"
      opening. Frequently I will have a small hole in the top of a
      pattern, for a woodscrew to draw it out of the sand. When the mold
      is all rammed up, and the cope is lifted off, I simply poke a scribe,
      or awl into that hole, or just tap it into the wood if there isn't
      already a hole. Hold the awl or scribe tightly to the pattern in a
      vertical position and place the open end of the rapper on each side
      of the awl right next to the pattern. Then just move the rapper
      rapidly from side to side so that both inside surfaces of the rapper
      are rapidly knocking against both sides of the awl. I do this from
      lef to right on the pattern and then switch and do it from top to
      bottom of the pattern. Basically you are just vibrating the pattern
      a miniscule amount from left to right and then top to bottom. What
      this does is to compress the sand a tiny amount AWAY from the pattern
      all around the pattern. You end up with a hole in the sand which is
      very slightly bigger than the outer dimension of the pattern, hence,
      the pattern will now just slip out. Here is a simple example which
      might help. Just extend your index finger on one hand and push it
      into a table top, then extend your index finger and middle finger on
      your other hand and slip the two of them on both sides of the first
      finger. Then just move the second hand rapidly from side to side,
      and you will see that they will basically vibrate the first index
      finger from side to side. This is all a hell of a lot easier to do
      than to describe. I figure the average person will have to practice
      it for about two minutes and you will have it down pat. I believe
      that this actually aids in giving you a slightly finer finsh on the
      sides of the mold too. Once again, this is how I was taught about
      forty years ago and it works great for me. There are some subtleties
      and fine points involved but they will become self evident to you
      once you try it. Hope this helps some.

      -- In hobbicast@yahoogroups.com, rgsparber@... wrote:
      > Gary,
      > Can you say more about how to do "proper rapping"? I'm fairly
      confident that
      > I'm not doing it right.
      > Thanks,
      > Rick Sparber
      > rgsparber@...
      > web site: http://rick.sparber.org
      > In a message dated 1/5/2008 10:25:48 A.M. US Mountain Standard
      > lekvoldgl@... writes:
      > and proper rapping will allow the pattern to just slide out as if I
      had used
      > 5 degrees of draft.
      > **************Start the year off right. Easy ways to stay in
      > http://body.aol.com/fitness/winter-exercise?
    • Stone Tool
      An excellent and most informative thread........ I m getting lots of good out of it........ Howard
      Message 31 of 31 , Jan 8, 2008
        An excellent and most informative thread........ I'm getting lots of
        good out of it........


        On Tue, 2008-01-08 at 05:54 +0000, Gary Lekvold wrote:
        > Hi Rick,
        > I never dreamed this thread would grow the way it has, but that is a
        > good thing, if it helps someone. A couple of points re: my initial
        > description. I said I rap left and right and then up and down. What I
        > should have said was, I rap in the X axis and then in the Y axis. In
        > many cases I rap all around in a circular motion. Once in a great
        > while I find it useful to rap very lightly in the Z axis, but not
        > often. What David said about gently wrapping while pulling up on the
        > draw screw is very important. It is also important to realize that you
        > only want to enlarge the cavity by a few thousandths of an inch. We
        > are not talkiing about fractions of an inch here. these are some of
        > the subtleties and fine points I was referring to at first. Just an
        > add-on thought. I bought the casting book by Ammen, at about the same
        > time I bought his plating book. I have never in my life seen how-to
        > books so full of gross mistakes and misinformation. I will not be
        > buying any more of his books.
        > Gary
        > --- In hobbicast@yahoogroups.com, rgsparber@... wrote:
        > >
        > > John,
        > >
        > > Thanks for the additional wisdom. I will have a lot of new
        > techniques to try
        > > on my next casting session.
        > >
        > > Rick
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