Yet another tenon problem

[RichC]

The slide on my old King DG doesn't fully tighten to the bell, though it is not bottoming out at the tenon. Easily fixed with a bit of paper but curious as to the reason. Is the taper off?

20230614_134453.jpg

[Doug Elliott]

I don't specifically know the structure of that but it could be bottoming out against something at the other end.

[Burgerbob]

Worn out. Seems to happen to those a lot.

[RichC]

I don't specifically know the structure of that but it could be bottoming out against something at the other end.

Thanks, Doug, but it's not hitting anything. There is a 'ridge' further up but the male part (of the slide) dosen't go that far up.

Worn out. Seems to happen to those a lot.

Aidan...probably, but I would have thought that either the slide would bottom out or there would be a groove worn inside the female part. This almost seems like the end of the male part isn't tapered the same as the inside of the tenon.

[Burgerbob]

Aidan...probably, but I would have thought that either the slide would bottom out or there would be a groove worn inside the female part. This almost seems like the end of the male part isn't tapered the same as the inside of the tenon.

I've had this same problem with a 6B or 7B. There was no bottoming out, but they didn't stay tight.

[RichC]

Aidan...probably, but I would have thought that either the slide would bottom out or there would be a groove worn inside the female part. This almost seems like the end of the male part isn't tapered the same as the inside of the tenon.

I've had this same problem with a 6B or 7B. There was no bottoming out, but they didn't stay tight.

How did you resolve the issue (assuming you did)? And, don’t say you sold the horn!

[ithinknot]

Kings have very thin walls at the end of the taper compared to other designs, which can be squashed inwards slightly over the years (or get out of round) in effect making the tenon more tapered than the receiver. That's how it can still stop the correct distance from the threads, but wobble internally. It's also very possible that the tapers never matched perfectly to begin with, and over the years it's become enough of a problem to be a problem...

The paper shim will probably be fine forever, or there's that copper anti-slug tape if paper gets annoying. The adhesive might not be great for the metal long term, but at least the copper shouldn't electrolytically misbehave, unlike aluminum foil tape.

[RichC]

It's also very possible that the tapers never matched perfectly to begin with, and over the years it's become enough of a problem to be a problem...

That's what I was wondering.

or there's that copper anti-slug tape if paper gets annoying. The adhesive might not be great for the metal long term, but at least the copper shouldn't electrolytically misbehave, unlike aluminum foil tape.

I wasn't familiar with that, but looking at it, might be useful. Thanks!

[CharlieB]

To satisfy your curiosity.............
Coat the tenon generously with black Magic Marker. Assemble the tapers and twist a bit.
Disassemble and study the wear pattern.
(Don't be surprised if the thin layer of marker ink is enough to tighten up the taper.)

[Doug Elliott]

I did that on a gig recently. The Sharpie ink was just enough to keep it from slipping.

[RichC]

Couldn't really see a pattern. But, it did work to tighten! Just have to add a sharpie to my gig bag.

[CharlieB]

No news is good news.You've proven that the tapers are parallel, and that there is no mechanical obstruction.
Don't tell anyone about the Magic Marker.
That's a trombonist's trade secret.

Seriously, what happens is after some trombones have been assembled a few hundred times, the surfaces of the tapers become glazed and lose their friction. The Marker (or the paper) temporarily restores the friction. If the marker becomes too much of a PITA, you might try breaking the glaze on the female taper with some emery cloth. In the picture, it looks like maybe the male taper has already been done.

[RichC]

In the picture, it looks like maybe the male taper has already been done.

Good eye! That’s the second thing I tried - after cleaning both surfaces, thinking that oil from the valve may have dripped down.

Thanks for the insight.

[CharlieB]

The only suspect left is the oil.
It likes to avoid surface cleaning by hiding in the pores of the metal.
The Magic Marker is alcohol based, so it cuts through the oil.