Surfing School - Glassing - Fin Box Templates
Fin boxes are not difficult to install provided you use the correct equipment and the proper procedure is followed. When glassing, don't make any special effort in the box area. However, if a box is to be used, make sure you have left sufficient blank thickness in the tail section of the board for the box to fit.
To begin with, you need to make a box template. If using different size boxes, it's best to make a separate template for each size rather than one adjustable box (like I have). The following method of template making is probably not the most efficient, but it will help prevent you from making a mistake that could force you to start over.
Cut out a piece of 1/2 inch plywood 2 feet by 2 1/2 feet using a table saw to insure straight right angle cuts and parallel cuts are made. Place the box you are planning to install directly in the center of this plywood piece (make sure it is centered at each end) and draw its outline on the plywood with a pencil. Next, using your router with a small bit (1/4 - 1/2 inch), and a jig saw, cut out the marked area to about 1/8 inch beyond the pencil mark. The small bit works best in the corners.
The corners should be as close to square as possible. The cut might be difficult as there will be some precise hand work involved. Using the 1/2 inch plywood will help prevent serious over-cutting the corners, and using a small tooth blade in the saw will help reduce rough edges along the straight cut. Go slow for best results. The figure 01 shows about what your plywood will look like.
After the hole is cut, put a 1/2 inch cutting bit in the router. Place your pencil on the outer edge of the metal flange holding your router, and with the router off, move the router around the hole. This will draw a second line on the plywood at the edge of the flange. This line will be the edge of the top board pieces that will prevent router foam cutting larger than the intended hole. The router cutting bit should fit just at the edge of the cut plywood.
Using approximately 1/2 inch by 1/2 inch boards, cut first two pieces extending the longest distance of the plywood flange mark, then cut a piece for the top and the bottom. These pieces should then be both nailed (use short nails) and resined to the plywood as shown in Figure 02.
After you finish attaching the top pieces, cut the outside edge of the plywood to about 2 inches from the attached pieces. I use a bench saw and make straight cuts from the bottom. Be very careful you line things up right so you cut even distances on both sides and don't over cut.
When completed, glue a thin piece of rubber (I used wetsuit rubber) on the bottom of the template and you're almost finished. The final activity is to mark the top and bottom of the finbox hole exactly at the middle. This mark will be used to line up with the board stringer when cutting the board's finbox hole.