Nov 30. Scarfing Plywood

Modern wooden drift boats are made from 16' long sheets of plywood. In the recent past, one could actually purchase plywood in that size, if you were near the manufacturer, say, on the Oregon coast, which was lucky because that's where drift boats typically were made. They were then called McKenzie Boats. I actually made the mistake of asking my local building supply guy whether I could get marine plywood in 16' sheets. He said that his supplier actually laughed out loud on the phone. Ok, I've scarfed plywood before. I can make a 16' sheet out of two 8' sheets. 

Last time I did this was 15 years ago and it was a laborious process involving a block plane and some serious muscle. (That scarf is still holding, BTW). But the plans I have are reasonably well detailed, including a 4-page pamphlet on how to scarf using a homemade skillsaw tool. I was skeptical, but a more thorough reading convinced me. 

Here's the tool. I made it quickly and easily using a chunk of ash I had laying around. It's designed to make a 7 degree edge cut. 

What really makes this technique work is the wooden straight edge clamped 3" down from the scarf on the plywood, on which rides the skillsaw tool, guaranteeing a perfect cut the entire length of the sheet. 

Her is a scarf cut on the edge of my plywood. This is half a scarf. The other piece of plywood is cut the same way and the two cuts are glued together overlapped. In this way you get a strong joint that is exactly the same thickness as the original material. 

One last word on the plywood. The plans call for Marine Grade Plywood due to the immense bending loads place on plywood used in drift boats. This is because marine plywood has no voids and will bend evenly without breaking. I wanted to see if it could be done with ACX grade plywood, which can have small voids. $150 in plywood instead of $300, too -- I'm cheap. We shall see. 

Glue up the scarfs tomorrow.