When forming bearing edges, the most important element that you must start with is an edge that is flat and true. This means when you put the shell on a flat surface the edge is touching that flat surface all the way around the shell. If you are not starting with a true edge, it makes forming a consistently shaped edge very difficult and in the end the drum will be difficult to tune.
Most people cut excellent bearing edges with a sanding table and a router table. The sanding table is simply a flat surface with sandpaper on it. A very effective sanding table can be made with melamine (particle board with a thin, hard plastic surface) or MDF (medium density fiberboard) covered with a sheet of countertop laminate.
Making sure this board is flat is the ultimate goal. If you attach straight-edged runners to the underside of the board, it will force the board to an acceptable level of flatness. Make the runners out of melamine or MDF also. They need to be wider than they are thick, so cut them to 3" wide on a table saw. The length will be determined by the size of the sanding table. Here is a suggested layout.
For the top of the table, we suggest using 120 grit or lower sandpaper. One method is to glue sheets to the table with spray adhesive. You can also purchase PSA (pressure sensitive adhesive) sandpaper rolls which are much easier to stick on and replace. They are available from Woodworker's Supply as well as other woodworking supply businesses.
Another sanding table option is to use a granite surface plate. This is basically a big slab of machined granite used for checking flatness. Some surface plates are very expensive, but for a reasonable price you can purchase a surface plate and stand from Grizzly Industrial. Go to www.grizzly.com or click here to go directly to the online catalog page.
Truing the Edge
Begin by rough cutting the bearing edge profile and leaving a smaller apex to sand. This is much easier than trying to sand flat the entire edge of the drum. Depending on how flat the edge is to begin with, you'll end up going back and forth between the sanding and router table a few times to finish up. In an ideal setup, you would have 2 sanding tables and 2 router tables. One sanding table would have a rough grit and the other a smoother grit for final sanding. For the router tables, one would be set up with your outer profile or countercut, and the other with your inner profile (usually a 45 or 30 degree angle bit).
Look at the graphic below. It is very difficult to obtain a flat bearing edge on a router table without leaving some amount of flat surface at the apex. If you try to cut a really sharp bearing edge as shown on the right, the point of reference for the surface of the router table is constantly getting cut away. If it is difficult for you to see if you have sanded the entire perimeter, use a pencil or some blue chalk to color the apex and sand until no marking is left.
Routing the Profile
We could argue all day over the "best" profile, the "right" place for the apex to be, and whether it should have a rounded or sharp apex. Experimentation is key here, and you need to find what works best for the sound you want to achieve. The shell type, hoop type, snare unit, and head type will contribute to the sound in conjuction with the bearing edge.
If you make your own router table, it is of course important that it be as flat as possible. You can follow the same guidelines for making a router table as you can for a sanding table. Melamine is very nice to use for router tables. Melamine is durable and smooth, and we suggest wiping on some Johnson's Paste Wax on the table occassionally to lower the friction. Simply wipe on a thin layer with a paper towel and wipe clean with a different paper towel. You will be amazed at the difference.
Commercial router tables are a good choice if you have the budget. They are well made and have features that can be used for other woodworking projects. The one below is a Benchdog router table. We have another table that we made ourselves that has a much bigger surface.
Here are some tips for getting good results:
Tape the outer surface of the shell to keep the bearing from marring the finish.
You don't really need a special bearing fixture on the top of the table if you've prepared your edge correctly and have a flat table. Don't rotate the shell like a steering wheel around the bit, but place your forearms on the top edge and move the entire shell in relation to the table and bit. This will keep even pressure on the router bearing all the way around the edge.
Notice in the above graphic that the apex has two corners. These corners need to be knocked down and rounded over by hand sanding after the machine work is done.
Seal the bearing edges using a clear sanding sealer (or vinyl sealer) and a foam brush. We cut a small notch in the brush to match the edge profile. Smooth out and finish the edge by applying Johnson's Paste Wax to 000 or 0000 steel wool then gently rubbing the edge. Be careful not to scratch the outer finish.
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