Issue with warped shell and how to solve it.

As you might have read earlier on the article about fixing a crack on the floortom, it looks like the shell is quite out of round. Well, it really is, about 6 mm (1/4") on the resonant side and 3,5 mm on the batter side.

I'm not too concerned about how a slightly out of round shell might sound bad or not, but rather about the head not fitting evenly and properly.

Here's what I did to reshape it without damaging it any further.

The idea is to secure the shell in shape by using perfectly round plywood rings, attached using the lugs mounting holes. To make fitting easier and to avoid having too much effect on vibration, the ring won't touch the shell, except at the mounting holes, through small beech dowels.

 

It seems to work, the diameter looks more consistent (about 2 mm variation). I can live with that, even though I was expecting less. Maybe I should design a more accurate / fine tunable construction.

Turning a shiny piece of plywood pipe into a musical instrument.

Like the title of the post suggests it, this one's about truing and routing the bearing edges to their final shape.

While doing it, I really felt like I was finally working on a musical instrument. I don't know, looking at the edges getting nice, smooth and flat, and thinking about the head resting evenly made me feel like the whole restoring process was even more worth it.

Here's how the bearing edges looked like when I got the drums. They had been recut, since SONOR drums from that era had round bearing edges, but the job was poorly done.

I started off by checking the height of the shell using a template, based on the lugs drill holes. I actually took the smallest height and removed 3 mm both sides. After sanding, edges should be flat and parallel, assuming the drill holes are perfectly aligned. Which is the case. C'mon it's German engineering.

The idea is to sand off just enough material to be able to route fresh bearing edges.

Afterwards, I built a router / sanding table with birch plywood leftovers (from my uncle's carpentry company).

As you can see on the picture, I'm using a 24"x18" phonic plus shell as a reference for checking trueness. By the way, the shell will be part of a next project that I - of course -  haven't planned yet.

The white marks help me sanding flat until enough material is removed.

This is a - discarded - large piece of sandpaper from a wide belt sander. Very convenient.

The re-cutting steps

1. Existing bearing edge
2. Edge flattened on the sanding table, 2 1/2 plies wide
3. Outside round out to 1/4th of the 2nd ply
4. Inside 45° to 1/4th of the 2nd ply
5. Careful finishing by hand, leaving a little less than 1/2 ply of head contact.

Outer roundover, using a 1/4" radius bit.

Still a tiny bit to go to get to 1/4th of the second ply

The inside 45 was done with a chamfer bit, working with very small height increments (0.25 mm) to ensure the cut doesn't go too far.

Finishing by hand, with P150, P240 and then some polishing with scotch brite

Always very complicated to take a good picture of the bearing edge, but it gives you an idea how nice it is now.