Reply by William Shelley

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Posted on Making your own finger-jointed stock?

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William Shelley

609 posts in 2350 days

#1 posted 08-03-2017 09:29 PM

Thanks all. I realize it’s a bunch of extra labor and that the return might not be great. In my case, I’m willing to trade time to avoid buying more lumber, and unless I’m totally mistaken, built-up stock is more dimensionally stable than solid pieces of the same species. The application for this is pretty much just picture frames, so not load bearing, not subject to wear and tear, and not subject to exterior or undesirable environmental conditions.

I know that the glue-up needs to be done well because uneven clamping pressure can give you a curved or ‘v’ shaped board, so I’ve got some ideas to solve that. The other issue to overcome is that, either the finger-joint end needs to be perfectly 90 degrees to the reference edge, or else the sum of the end-angles of the two boards needs to add-up to exactly 180 degrees.

I enjoy designing and building machines and jigs as much or maybe more than I enjoy actually producing end-user items. My idea here is to use a dedicated router with a finger-joint bit installed that will travel along one axis perpendicular to a fence that extends left and right (and is dead straight), and allow me to cut the ends of the boards to be joined at exactly the same/opposite angles. Board A would be placed on the left, and it’s right-end would be cut, and board B would be placed on the right, and it’s left-end would be cut. As long as the fence that they both register against is perfectly straight, then it won’t matter if the angle of the router’s travel axis vs the fence is not 90 degrees.

For clamping, I’d probably make a flat L-shaped reference surface and use some of my spare pneumatic cylinders mounted at a 45 to 60 degree angle, with a swiveling rubber pad on the end. The cylinders would push down, and away, and force the boards together, but also push the face against the reference surfaces, so the result should be a pretty damn straight board after glue-up.

One thing I’m not sure on is what type of glue to use that will reduce telegraphing of the glue line through the paint.

I know that Urea-Formaldehyde glue would probably do this but it has to be mixed up and is toxic to work with, so something in a bottle would be preferable.

-- Woodworking from an engineer's perspective

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