Whichever type of construction is used to make the shell, the bearing edges are crucial to the sound, projection and tuning of the drum. Modern bearing edges are usually routed to an almost sharp point, typically cut to a 45 degree angle on the inside of the shell, while the outer cut will also be 45 degrees or rounded over so that the head transfers vibration to the shell when it’s tightened over the edge.
The inner cut will usually be deeper than the outer cut, thus maximizing the diameter of the drum. The fact the bearing edge is sharp means the attack and projection of the head are increased. This has not always been the case. Vintage drums often have much more rounded edges so that considerably more of the head is in contact with the shell. This gives a warmer, less attacking sound and theoretically imparts more of the character of the shell. Other shells have different routed angles. Gretsch toms, for example, have 30-degree inner edges for a warmer sound, while Gretsch snare drums have 60-degree edges for attack. Specialist manufacturers Pork Pie Percussion use a 60-degree inner cut with a rounded-over outer edge to achieve maximum vibration of the shell.
Spaun drums have an equal 45-degree cut both inside and outside, rising to a central, sharp epeak’. Spaun say this means the edge makes contact with the flat part of the head rather than the rounded collar, improving tuning and head resonance. Another way of ensuring the bearing edge contacts the flat of the head and not the collar is to make the shell slightly undersized. So although a shell may have a nominal diameter of, say, 12”, in fact the shell is slightly less than that.
The Premier Series shells, for example, are all 3mm undersized. This way a gap is opened up between the standard sized metal rim and the shell so that when the standard sized head is fitted it cannot be cramped between shell and metal rim. A sort of bridge is created which should aid the free resonance of the head n and shell. There’s always an opposing philosophy, though, and I remember once reading a handout from the Slingerland company claiming that the fact that its vintage Radio King shells were tight against the hoops was one factor in the unique sound of these sought after old drums. Whatever the shell size, the bearing edge must be perfectly true all round so that the head can be tensioned evenly, achieving the same pitch at each tension point.
This is one of the most crucial aspects of shell construction. Any slight dip or irregularity in the bearing edge will result in a dead spot in the head, which will have to be accommodated in tuning. This distorts the head and messes with the overtones. If you have a problem drum in your kit, which is always infuriatingly difficult to tune, then it might be worth inspecting the bearing edges for irregularities.
Note, however, that the bottom edge of your snare drum is an exception. It should have two slight dips n one on each side n where the snares are attached to the shell. These dips are known as snare beds and their purpose is to help the snares lie flat, reducing snare buzz. On old drums the beds may be quite pronounced while on modern drums they are more likely to be very gradual depressions spanning several inches.
They may only be noticeable on careful inspection. Since resonant snare heads are very thing they mould easily to the slight dip. You will, though, have to give the tension rods on each side an extra tweak to smooth out the wrinkles.