Today I attempted to realign the 3rd valve slide on a Laskey-Pinc gold-plated trumpet. In addition to the slide being out of alignment the 3rd slide stop screw, which is threaded through the brace on that slide, was really tight and wasn't threading in at a right angle to the slide. It was slightly askew.
I found that the problem with the alignment was on the outer slide. The span between upper and lower tubes was not parallel, being about .005" wider at the ends of the tubes than at the brace that holds the slide in alignment. As I expected, the upper tube (which is an outer slide - the lower tube is an inner slide) was bent upward right at the brace. I expended a great deal of energy carefully trying different approaches to bend that slide back into alignment and make it parallel with the bottom tube, but after about an hour of trying it hadn't budged at all, even with a jig a put together that used a trombone handslide mandrel and a table leg for leverage. At that point I had to take a step back and consider this: If all the pressure I had exerted on the slide hadn't moved it one iota, then I was clearly going about things in the wrong way. Something had to have forced it out of alignment, but if the slides were that tough then it couldn't have been some conventional damage like a bump or a twisting of the slide. Something more complex and far stronger was at play.
It was at that point I began to reconsider the slide stop screw. The threads through the brace were really messy and looked chewed up. This in comparison to everything else on the instrument, which appeared to have been carefully machined, aligned, and assembled. It is a handmade trumpet, after all. It then occured to me that the stop screw threading through the brace at a skewed angle couldn't have been part of the original design, and it was likely that the screw had been cross-threaded by some mistake at some point. I called the customer to see if he could shed any light on the matter and, sure enough, he told me that he'd recently had the instrument apart for cleaning. While reassembling it he started to have trouble getting that screw to thread into the brace, so he repeatedly ran it forward and backed it out incrementally, in exactly the same way one would cut threads with a tap. That explanation made perfect sense, and it suddenly occurred to me why everything was going wrong.
When he was having trouble threading that screw, it was because he had started to crossthread it. Normally a crossthreaded screw will only turn a few rotations or less before completely binding up, but because the screw is made of steel, which is much harder than the brass in the brace, he was able to actually recut the threads in the post at an angle by being patient and running it in and out like a tap. Unfortunately the screw, having no reliefs in it like a tap, didn't just cut material out of the threads and clear it away. It displaced some metal, too, and in the tight confines of that brace stuck between two tubes, that metal went up and out, effectively making the brace taller by a practically microscopic amount. That was enough, though, to cause the brace to push the tubes farther apart, forcing the upper tube to bend slightly upward right where it is soldered to the brace. That was why my prior attempts to straighten the upper tube had failed - because the amount of force required to bend a piece of tubing in the exact spot where it's soldered to a rigid and substantial brace is massive. Somehow, though, that little steel screw had managed to put just that amount of force on the slide and cause the alignment issue.
With that little bit of detective work done, I was able to plan a new strategy. I called the manufacturer and actually got to talk with Ron Pinc, who makes all the slides, and checked the correct thread pitch for that screw (it's 4-40). Then I recut the threads in the brace (after running out to the store to buy a new 4-40 tap, as I discovered ours to be broken) and on the screw. With the screw working properly again, I moved on to bending the tubes back into alignment. Remembering that I saw an amusing infographic a few days ago about tourniquets and how they can be used to apply and maintain incredible amounts of pressure, I rigged up a tourniquet around the slide tubes right at the brace point, and literally pulled the upper tube back down toward the lower tube. Success! With just a couple of tries I was able to straighten the upper tube and realign the slide. A few more tweaks to align it to the slide tubes on the instrument are needed tomorrow, and things will be back in working order.
It may seem mundane, and even I didn't think such a small job would merit so much writing, but I was excited to do some real diagnostic detective work and discover how the damage had been done to that instrument in the first place. If you can figure what caused something not to work, you can almost invariably figure out a way to make it work again. Through patience and a methodical approach, I was able to just that, and it felt pretty great.
UPDATE: I also learned that you can't wipe excess solder from a solder joint on gold plate, because the solder will just go EVERYWHERE.
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