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building bows-- the taper, degrees of precision?

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  • Bernard Arnest
    Hi, With Bingham s plans, I m wondering about the taper... Full height on one side, 58 thousandths lower on the other. 1/16 is 62.5 thousandths, so it s a
    Message 1 of 1 , Mar 2, 2004
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      Hi,
      With Bingham's plans, I'm wondering about the taper... Full height
      on one side, 58 thousandths lower on the other. 1/16" is 62.5
      thousandths, so it's a taper of less than 1/16" across 2 1/2 feet of
      the tapered lamination strip. I could get two strips of plywood, then
      raise one of them up .058". Lay the now parallel piece on it, run it
      through the thickness sander, and voila, a taper. But after resawing
      pretty thin off of a 1" board, it has bowed (no pun intended). Wood
      just does that when it's cut, the thinner it is, the more internal
      stresses show themselves. So while when running it through parallel,
      the drum pushes it down and sands it evenly despite the bow, that
      won't be the case when it's sticking up at an angle in the taper jig.
      It won't be sanded to a perfect taper. Even if it's flat, there's
      the issue of making an adjustable length jig, and the force of the
      drum pushing it off of the jig, etc., etc. So I'm just concerned that
      even with the most exact tools out there, namely a precision thickness
      sander, it still won't be perfect.

      And then it won't be exactly 2" wide, either; in fact, it looks like
      this piece might fall just over 1/16" short. And the fiberglass is
      only approximately .009" thick, I'll try five layers on the front and
      5 on the back and see what it does; but one can never tell. Maybe a
      pocket of epoxy even under pressure will make it thicker in one spot.
      And depending on whether I use zebrawood, walnut, maple, or bamboo;
      and depending on whether I use E glass, S glass, or carbon fiber......

      What I'm really asking, is that would it be ok to carefully taper it
      by hand with a scraper and sanding block? As crude as that might
      sound, it might be more accurate than attempting a jig for the
      thickness sander, especially granted the slightly warped lamination
      strip. Given all of the inaccuracies there are, I have a feeling I'm
      going to have to just laminate it, drill the holes to match the riser,
      tiller it, and put it on the scale and see what it is. The worst it
      could be is underweight in which case I'll deal with it or if
      extremely so add another layer of fiberglass; and if it's overweight I
      can just sand some of the fiberglass off.... What do you suggest, is
      it ok to try to taper it by hand? My feeling is that others have made
      successful bows for centuries and millennia without digital calipers
      and thickness sanders, and even today there are so many other factors
      that I'm going to be making adjustments after lamination anyway; but
      I'm not sure.....

      thanks!
      -Bernard
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