Scarfing

What to do when the plan calls for a 20 foot long piece of Sapele and you can only find a few measly 12 foot lengths? Well, you just make a longer piece, obviously.

Scarfing joins two (or more) shorter peices into a longer (or much longer) one by beveling two edges so they have a relatively huge surface area, then glueing and clamping them into effectively one piece of wood. Angle is everything in the scarf – for each inch of material thickness, we want 12 inches of material length for an optimal joint. It’s critical that both bevels are cut at the same angle so the finished piece will lie flat, and that we avoid any lows or highs in the cut surface that can cause the epoxy to cure unevenly (or worse, leave voids).

Fortunately, there’s an easy way to do all of this.

The scarf jig is a very simple tool to cut an even angle acros the two pieces. Simply take the thickness of the piece, multiply by twelve, and draw a line across the first piece of your scarf material. Align your second piece of scarf material with this line, and then draw a line on the second piece. Clamp it down real nice, and you’ve got yourself a scarf jig.

Get out your power plane and start working, because you’re remooving a lot of material when you’re working with these big pieces. After a few hours, it’s close enough to smooth that it’s time to switch to a hand joiner plane to even things out. Important note: you can use the plane base as a straight edge to check for levelness, and a flashlight to spot any highs or lows by the light that leaks through.

Once finished, the mating surfaces aretest fitted, and then epoxied. First a layer of unthickened epoxy is applied to soak into the endgrain, then a layer of epoxy thickened with colloidal silica for bond strength. Finally, a layer of clamps complete the setup.

 

Across the shop, work continues on fairing and matching the bedlogs and setting up the strongback for construction. There’s a lot of measuring, remeasuring, squaring, remeasuring, nudging, remeasuring… you get the idea. We want the strongback to be perfectly square and level so it can be used as a reference datum for the contruction of molds.

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