Dettloff Music and Repair

This was a fun little project: this trumpet came to me missing a draw knob on its second slide, and we don’t have any spare ones that match the characteristic Getzen hexagonal knobs. I’ll make one! I started by looking at the knob on the 1st slide, taking some measurements, and doing some triangle math to figure out exactly how long each side needs to be.

I started with a round piece of brass stock, and filed it to the largest radius I’ll need when I create the hexagon. Then I set my calipers to the length of each side, and marked my six points around the circle. I filed each side into a flat, then sanded them.

I know there’s a more exact way I could do this, but I’m trying not to take too much time on it, and though the sides aren’t perfect, it’s looking pretty darn good. On the lathe, I used a scribing bit that had a more blunt tip (not blunt as in not sharp, blunt as in not pointy) to match the groove in the original as best as I could. With some small files and sandpaper, I add the curve to both the top of the piece and the underside of the groove.

The trickiest part of this was creating a radius on the bottom to match the radius of the tube I’m putting it on. Our half-round files are too large, the fully round files are too small. We have an accessory for a Dremel that matches the radius really well, but the Dremel was aggressive and doesn’t offer much feedback to help me stay centered on the part, so I ended up with a curve that was too flat anyway. I did some work with my half-round and rat tail jeweler’s files to try to get it as close as I can without taking away too much more height from the part (I’d lost a lot of height to the Dremel). It’s not bad! After soldering, the minor gaps where the radii didn’t align properly look even more minor, and this is a decent replica for an afternoon’s work. I’d love to take another crack at it someday to get it more exact.