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| Kyūzō from Seven Samurai by Akira Kurusawa |
I wish someone would give me a whole box of those sharpening guides and gizmos... so I could have the pleasure of dumping them overboard!
-- Dynamite Payson (as remembered)
Learning to Trust Myself
I'm one of those guys who spends an inordinate amount of time trying to find the easy way forward. Sometimes, this effort pays handsomely. Other times, I waste my effort in attempting to fix what ain't broke.
At present, we're building a boat in at least semi-traditional style. That is to say, it's plywood, but fastened and bedded -- rather than glued -- together. Mostly. The critical joinery must be carefully and correctly shaped without reliance on modern, gap-filling adhesives. This calls on skills which are rusty at best and at worst heretofore unacquired.
Two cases in point...
Rolling Bevels
Rolling bevels are a cut along an edge where the bevel is not constant, but rather rolls along a gradient between known angles. This kind of loosey-goosey process is terrifying to my ordered mind, and I have successfully eliminated them from TriloBoat construction.
We once were drafted into a professional effort to roll a bevel along a long, thick, expensive plank. One pro ran the plank through a bandsaw while another called out angles marked at intervals along the plank. The angle of cut was changed by angling the plate with a protractor/handle arrangement. Our job was to shift the handle "slowly" and "smoothly", transitioning between the angles being called out.
I mean, c'mon! I can call out numbers as they slide by me with one eye covered. But to make the correct transition? THAT is a pro job foisted upon us amateurs.
But now, we're faced with rolling bevels in our own build, on our own petard.
Back to first principles: We basically have two, parallel faces. A fair curve along one edge is known from the plans. We know the edge angle at several points along that curve and also that they are increasing -- slowly and smoothly -- at known points along its length. Hmm. So if we figure out (by a simple lofting) the offset each angle makes across the thickness of the piece and plot those points on their stations, we can draw a second fair curve on the second face. Plane the edge to meet the two curves and voila! The perfect curve, de-terrified.
Ply Scarfs
For various (probably trivial) reasons, we chose to scarf the ply sides together rather than use our usual butt-straps. Conditions dictated 8in scarfs for 3/4in plywood.
Now there are an endless number of jigs possible for this, but they take time, materials and brainpower likely exceeding the job itself (in our one-off case).
First we tried the method we used on SLACKTIDE... step each sheet back 8in, fix a 2x4 runner to our circular saw to bridge the 'steps' and, with the salient depth set to 3/4in, have at.
Having at means scoring along at about 1/8in intervals, knocking that thin wall out with the blade and, using intact steps to support the 2x4 and saw, side-sweeping the flat with the tangent of the blade.
This works, but is strenuous going. I took it in stride 16 years ago, but am huffing and a-puffing, now! Worse, unlike in SLACKTIDE, our present ply finished rough with this method.
Oh well, score the steps less frequently and use the planer to the depth they indicated. But, hmm... that turned out rough, too. What's more, I did 99% of the job with the planer by eye, then carefully removed the last smidgeon guided by the scoring.
Conclusion? Try it by eye as the sole means. Result? Better results in half the time with only a quarter the effort.
In short, I'd have save myself a lot of time and trouble, wear and tear if I'd trusted myself from the beginning. Sure, there's a learning curve, but no worse than more involved methods.
NOTE: We use LPU (Liquid PolyUrethane), a modern, gap-filling adhesive, for ply scarfs, so the matching planes don't have to be utterly perfect... just good enough.
*****
We d0 need to be clear on the principles and constraints involved. I'm not talking Blind-Man's Bluff, here. There is a certain amount of letting go and winging it, but that lies in our increasing control of our bodies first, and of our tools as extensions.
We have the luxury to inform ourselves from past masters and present. We have the luxury to practice on scrap. We can Assess, Address and Appraise.
So... ready, set, practice, go and get 'er did!
