Cracked Tone Ring

I'd initially noticed one of the bolt holes in the tone ring had been over tightened causing a piece of the pot metal edge to break off. At the time I decided to just leave it be but yesterday whilst I was using a little vice to try and straighten out each of the warped brackets as best I could I noticed the edge of another bolt hole was cracked. The crack extended from both sides of the hole and it needed addressing because if the instrument ever gets played the crack may rattle and even worse left unchecked may grow and render the instrument useless.

Normally you'd dissemble the head and weld the crack but I don't know how to weld and don't have access to a welder. I also didn't want to fully dissemble the head as I suspect the vellum might not survive removing and refitting the tone ring. Luckily these days there's some alternatives to welding. I popped to Halfords and returned with a pack of Plastic Padding Super Steel Epoxy Weld, a metal filled two component adhesive. The blurb said it could be used to replace lost metal and showed a propellor wth a blade missing so I figured it was probably up to repairing a crack in a pot metal tone ring. As it could replace missing metal I decided to fix the other broken bolt hole too.

To avoid blocking the bolt holes I inserted round skewers bound with cling film. Mixing up some epoxy I pushed it into the crack and built it up above and below to provide extra support. To repair the missing piece of metal I used masking tape to form a gantry which I then filled with the epoxy. It's meant to dry in five minutes according to the blurb but it didn't where I was rebuilding lost metal -possibly because of the thickness. After a half hour I removed the skewers, cling film and masking tape and filled back the excess epoxy. There were a few places I thought it should be thicker so I mixed a little more and positioned it with a skewer. Then I went swimming. Well who's going to sit about watching glue dry? Returning, better for some exercise, I got out a few files andonce again tidied up the epoxy.

The dried epoxy had a dark shiny surface but once filled became matt and matched pretty closely to the colour of the tone ring. I think the tone ring is most likely some sort of pot metal basically a cheap mix of metals but mostly zinc, melted at low heat. Looking at the edge of the head I could see the hex bolts had quite visibly been overtightened in the past. This has buckled the tone ring and quite likely contributed to bending the brackets.

The Tension Ring (top metal bit) was a bit grotty so I wiped it down with naptha on cotton wool as I went round removing and straightening the z brackets one at a time. I also gave the surface of the vellum a rub down with a soft rubber eraser although I'm not convinced it had any effect. As you can see in the above images below the vellum is a sirt of dry excess vellum which should've been trimmed back once fitted. Over the years it's hardened to the point it fels like plastic. It probably effects the sound on the instrument possibly acting as a dampener so  I tried trimming it back with a scalpel but it was far too hard to cut. I could probably do it with the Dremmel but didn't want to risk damaging the main disc of vellum so for now I'm leaving it in place.