Fix for Drifting Bell?

[bobroden]

Is there a standard “cure” for when a bell unit doesn’t want to stay tightly in place in relation to the slide?

I’ve had a number of horns on which the bell wants to drift downward, toward my feet, when the horn is held in playing position. Sometimes this happens no matter how tightly I screw down the connector between the two units.

It has happened on newer horns as well as older.

The best I’ve been able to do is push the slide and bell units together as tightly as I can before tightening the connector. So I’m just wondering if there is a conventional fix for this problem that perhaps I’m not aware of. Maybe plumber's thread-sealing tape or something?

I have to believe this is a common problem, right?

[Burgerbob]

The threads don't really matter here- the tapers should keep the horn together by themselves. The threads are just for safety.

I recently had John Sandhagen cut down a thread on my Edwards dual bore slide, so that it would go in just a BIT farther and not flop over. It fixed the problem.

[OneTon]

Yes. Common problem. Most often a common fix.

[JohnL]

As Burgerbob said, the threads are secondary - there should be enough friction in the joint to hold even without tightening the nut at all (older "friction-fit" trombones don't have tenon nuts).

The first thing to try is to thoroughly clean the mating tapers. Oil or other "stuff" can cause the joint to slip.

[ithinknot]

If the tenon bottoms out before the taper grabs, then the end of the tenon gets filed down until it stops getting in the way.

This works several times, but there's only so much scope until the receiver end starts bottoming out on the threads. At this point either a thread needs to leave, or the receiver needs trimming. If the retaining flange for the bell nut is a soft soldered ring then it can be moved back and the exposed excess be filed flush, but if it's brazed or machined from solid stock then things get trickier.

This is all assuming the tapers still basically match and nothing's been significantly distorted or unevenly worn.

[PaulT]

Don't jam the slide tenon straight in. Twist/turn/rotate it in.

To begin, insert the slide tenon into the bell so that the two form a 180 angle (straight angle. the two are typically at a 90 degree angle when in playing position). Then, while exerting a slight amount of pressure, twist/turn/rotate the slide into a 90 degree playing position. The tenon joint will tighten up as if it is being screwed in (the taper will do the work).

You will very likely discover that by starting at 180 degrees (flat) the tenon will tighten up well before the preferred 90 degrees is reached. No problem, start again with a lesser angle. Through practice, you will discover the best starting point and just how much twist and applied pressure it takes for each horn to reach a tight, snug, and holding fit. (for example, it might well be 120 degrees instead of 180).

When taking the horn apart, don't pull, just twist/rotate the slide the other way (in effect, un-screwing the tenon joint).

If you are holding the horn with mouthpiece towards you and the bell away, the first twist/rotate to tighten will be counterclockwise (right to left). To loosen the tenon's hold, twist the slide clockwise, left to right.

You will get the hang of how much twist and how much pressure in no time.

Do not jam/push. Twist/turn/rotate the tenon in while applying slight pressure.

[bobroden]

Thank to all of you all the excellent advice. I just tried PaulT's method and it worked well. I'm sure this is a common issue, so I hope this brief thread finds its way to everyone who could use the info.

[Rob1662]

I had Rath fit their tenon and clamp to Kanstul 1662, cured the dreaded problem once and for all.

[Posaunus]

Don't jam the slide tenon straight in. Twist/turn/rotate it in.
... ...

Excellent suggestions, Paul. I think I have been doing this instinctively for years, with great results.

Does this technique work with your "slide kazoo?"

[bobroden]

I had Rath fit their tenon and clamp to Kanstul 1662, cured the dreaded problem once and for all.

Nice! The Rath system is definitely a huge improvement on this issue.

[baileyman]

My Bachs all snug up with the slightest rotation. It seems if more rotation is needed there must be something on the surfaces acting as a lubricant. Or else there is an error in the taper. These tapers reliably hold machine tools together, so a trombone should be no problem.

[gbedinger]

I played a Yamaha 822 for 10 years…I have the greatest respect for them, but while attempting to tighten the bell section to the slide, I would get a drift right off the bat. Knowing that, I would make a similar “snug” rotation (as has already been described) and the problem was solved.

I did attribute it to the weight of the bell section and lack of torque I was able to give to the screw clamp (owing to the second valve lever) but it was not a factor once I figured out the sequence.