building bows-- the taper, degrees of precision?
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.....