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Strip Planking 01: Cutting Forms for Strip-Built Kayaks [video]
The first step to assuring your boat comes out right is to assure you have accurate forms. You could buy a kit with pre-cut forms made on a CNC machine, but if you want to do it all yourself, cutting the forms from the paper patterns provided in the plans is not hard.
The patterns in the kayak plans from Guillemot Kayaks are all full-size and drawn out in full. This means you can just glue the plans to your forms material and cut out around the lines. Cut out each individual pattern leaving about 1/2" around the outside. I typically use Medium Density Fiberboard (MDF) for the forms because it is dimensionally stable, doesn't have any interior voids and holds a staple pretty well. It is a little heavy, which for a large boat can make the set-up strongback with all the forms may be heavy, but if this is a concern, you can cut holes in the forms to make them lighter.
In this case I bought 2 foot by 4 foot pieces of MDF from the local big-box homecenter. This size is easier to handle than a full 4x8 sheet. It is lighter and fits in the back of most cars. It costs a couple dollars more than the equivalent amount of material in a full sheet, but the convenience may be worth it.
I lay out all the patterns on the MDF seeking an efficient arrangement that uses as little material as possible. I start with the patterns up-side-down so I can spray them immediately after I find my arrangement. I use a spray adheasive such as 3M Super 77, spraying a mist over the back of the patterns, then lifting the patterns and spraying the MDF. Align the patterns back in place, then start by sticking down one edge, holding up the other while you wipe your hand from the stuck-down end to the lifted-end. This way you won't get wrinkles in the pattern.
Next, roughly cut out each form as shown in the video. This makes the pieces easier to handle when you go to make the accurate cut. Just hack the pieces out, don't worry too much about the outline, just cut into the actual form.
With a bandsaw, cut around the outline. I cut in a clockwise manner, with the form to the right of the blade and the scrap going to the left. Cut right up to the line, leaving the line to pass just to the right of the blade. I generally try to make this my finished cut. If you are having trouble keeping close to the line, you can sand down to the line later with a table mounted belt or disk sander.
On tight rounded corners, you may find the blade wandering away from the line. Back up the forms slightly and cut back on the line.
On sharp corners such as hard chines, cut straight past the corner, then come back and cut on the new direction.
With an internal strongback for a kayak, you need a hole cut through each form. It is important that this hole is accurate. I accomplish this in a couple steps. First I drill holes at each corner, just inside the line. Then I saw out the bulk of the material, leaving about 1/16" to 1/8" from the line. Then using an accurately cut template, I use a template-following router bit and a router table to make the final accurate hole.