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Home Tech - Drum Building Cutting Bearing Edges
Cutting Bearing Edges

Bearing edges:

Cutting bearing edges is not an impossibly complex operation but there is enough equipment and set-up required that some builders defer to letting suppliers cut the edges. However, once you've constructed an edge-cutting set-up, you can then not only cut new shells but also re-cut old drums which have crappy bearing edges.

 

The secret to cutting a decent bearing edge is to use a router with a 45 degree chamfer bit. You want to get one that has a small ball bearing that rides on the wood below the cutter. The idea here is that the ball bearing serves as a guide to the cutter so that just so much wood is cut away.

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There are two types of set-ups that work well. One is a router mounted in a large area table. It works very well for smaller drums, but a bass drum can require a pretty large surface to stabilize it as you cut. Therefore, I opted for a set-up where the router moves and the shell is stationary. What I did was get a long piece of plexiglas about 1/2" thick by about 6 inches wide and long enough to more than span the largest bass drum I want to cut a bearing edge on. I mounted the router (which in my case was just a small hand-held unit used for trimming formica installations) on one end of the plexiglas "board". You use plexiglass rather than wood so you can see what you are doing. Install the cutter and that's the whole tool! Since the cutter ball bearing rides against the surface of the shell, you adjust the amount of wood you are taking off by raising or lowering the router in it's holder. The lower you push the cutter down, the more wood you take off. I'd suggest starting with just tiny cuts to get the feel of things and then slowly adjust the depth until you are taking just the right amount of wood off the shell.

The trick that makes this thing work is that you have to be *very* careful never to cut all the plies in the shell. There should always be one single play left that is un cut and acts as the guide that holds up the cutter on the "board". If you cut too much you may get a "step" in the edge as the cutter will lower itself as it finishes the cut. If the original cut on the shell has a "step" in it, that also will cause trouble when cutting a bearing edge. Luckily, if you do get some tiny steps, they are easy to sand out by hand.

There are two common styles of bearing edges. One is just a straight 45 degree cut with the low side on the center of the drum. This makes a bearing edge which is truly 45 degrees. VERY sharp!  This has the most sustain and harmonics, but has the disadvantage that the head doesn't center so well as can be tricky to tune.   So some people opt for a 90 degree edge. In this edge you cut a 45 degree edge as above slightly more than half way through the shell and then move the cutter to the OUTSIDE of the shell and chamfer the edge on the outside as well. This edge will also sound great and will be easy to tune and change heads because the actual edge is a smaller diameter than the single cut bearing edge. The outside chamfer tends to center the head making tuning easy.





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