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Ed Claxton's old time

Marine Drafting Weights

© Frank Ford, 12/8/00; Photos by FF, 2000

On my most recent trip to Santa Cruz, I stopped in to visit Ed Claxton in his shop.
If you haven't seen or played one of Ed's fine guitars, you've missed a real treat.
He was in the midst of designing a new body shape when I walked in, and I must admit
he surprised me with this amazing old timer's technique for drawing perfect curves.

Ed had spend some time designing and building wooden boats, and had picked up some
interesting tricks of the trade. This is one of his favorites.

Now, he made these lead weights himself, using the "whale motif" of the
old time marine architect tool. He was quick to suggest that the shape is not significant
at all:

What *is* significant is the pointy rod sticking out of the end. The exact weight
is also not significant - these weights are fairly heavy, a pound or two each.

To get a perfect, regular curve, he simply sticks the weights on a thin strip of
perfectly clear white pine, bends it to the shape, and holds it in place with the
weights:

Ed says white pine is the most regular bending wood he's tried, but he stresses the
fact that almost any really clear grain wood will do nicely. The exact dimensions
of the wood aren't significant, although it must be consistent in thickness and width,
and bend easily to the curves desired. He has several thicknesses for different radius
curves.

Now, here's the really cool trick:

First after sketching the outline roughly, Ed lays the curve approximately where
he wants it, and holds the curve in place with the weights. Notice that the entire
weight is held about 1/8" off the paper by the rod, leaving only the tip of
the tail in contact with the paper.

Then, he goes around the curve, lifting and replacing each weight in turn:

Wow! Just like magic, the wood strip springs out or in just a teeny bit to smooth
out the curve. A couple of trips around the curve, and it comes out perfectly aligned.
For sure, this is a trick that works so well, it is really not possible to describe
adequately. You really should see it in action.

Working a section at a time, he gets each curve just right:

Total working time was almost nil.

Of course, it's no trick at all to draw a pencil line along this strip:

One thing for sure, before I try to draw out another body shape, I'll make some of
these little weights for myself!

"I teach CAD at Orange Coast College, and these devices
are classic drafting implements. Variations are used by everyone who has to design or build irregularly curved objects such as boats, planes, cars, or complex roofs. They go by various names depending on who's using them, but the ones I hear most are car-related: The wood strip used to "fair" (smooth) the curve = spline Weights used on spline = ducks Of course, roofers who lay out "eyebrow" shingled roofs just use a straight strip of plywood and a couple of nails, but boat and plane designers are much more elegant. Now the nerd in me had to research this (and you're closer to the CG community than I am), but the first person to mathematically describe what was going on in the '70's was Pierre Bezier of Renault - you know, of "Bezier curve" or "Bezier spline" fame. And the formula? A mathematical translation of curves and weights (AKA a spline and a set of ducks). Now that computers can create NURBS (Non-Uniform, Rational, B-Splines - whew!) students have no idea how people used to get smooth, free-flowing curves - curves virtually impossible to accurately get from French curves. But show them a spline and a set of ducks and it's like magic. Thanks for reminding me of these great practial tools." - - - Darrell Urbien |