Monday, June10, 2002 - Scarfing the Dash Bulkhead: Today I started making the dash bulkhead. The bulkheads are the interior "walls" of the boat. Besides dividing the boat into sections, the bulkheads combined with the planking are what give the boat most of it's strength. This bulkhead is going to be a little over 6 1/2 feet wide and 4 1/2 feet tall. In addition, the plans call for the grain in the bulkhead to run vertically. What this means is that I will not be able to use one 4 X 8 sheet of plywood, but instead must join two pieces of 4 X 8 pieces of plywood together to get a piece big enough to cut out bulkhead. In order to do this properly the two pieces must be beveled, overlapped, and glued together. That's called scarfing.
The first part of scarfing is figuring out how wide to make the bevel. I use a ratio of 12:1. The plywood is 3/4 of an inch thick, so the bevel is 9 inches across.
Here I have set the plywood on horses and am marking a 9 inch line off along the 8 ft. side.
The next step is to start beveling the plywood. When I'm working with 1/4 inch wood (4mm) I always use a low angle hand plane. For anything larger I use my Bosch 3272A Electric Planer. The trick to using this plane is to start by setting the plane to cut at 1/32 of an inch. As the bevel gets closer and closer to the bottom of the leading edge of the board, I reduce the cut down to 1/64 of an inch. The reason for this is that as the plywood gets thinner it is prone to shattering. When I get about 1/8 of an inch away from the bottom of the leading edge I stop and use my Craftsman 1 HP 3 inch Belt Sander. Notice in the pictures below that I have rigged the exhaust on both of these tools with plastic tubing and hooked them up to a Rigid 6.0 HP Shop Vac. The shop vac gets most of the dust.
My planer and vacuum attachment.
Making the scarf.
Checking the scarf to make sure that the bevel is even. This is very important because the glued surfaces should match as evenly as posible.
Sanding the bevel - the edge is getting paper thin.
The bevel about 90% complete. If you get it just right, all the veneers will be evenly space and the top line will be partially sanded off. (Before gluing I redraw the line to facilitate the glueing process.) It's OK if the edge of the bevel has a few chips out of it.
I use this Jet Air Filtration System to eliminate some of the dust in my shop. I opted for this system instead of a single stage dust collector system because my shop is relatively small and I like to roll my tools outside for really messy jobs.
I can usually scarf two 1/4 inch boards together during one session, but setting up and beveling a 3/4 inch board takes a little more time. With the Florida heat building in the morning, I decide to retreat at about 11:00 am!!!