Rotor Bumpers Dried out and Cracking

[Fireinthebones]

On my Bass Bone the rotor Bumpers are all ripping I might order new ones but I am just genuinely curious was there something I should have done to prevent this from happening. ie. some sort of moisturizer on the bumpers. ( I bath my trombone every other month or so)

[Bonearzt]

Nothing really will prolong their life and they are cheap enough to just replace occasionally.

[tbonesullivan]

What kind of rubber is being used for the bumpers? Most modern rubbers are pretty impervious to chemical degradation.

[boneagain]

You say you are ordering new ones.
Are you fully versed in adjusting new bumpers?

[Fireinthebones]

You say you are ordering new ones.
Are you fully versed in adjusting new bumpers?

My Instructor will

[timothy42b]

You say you are ordering new ones.
Are you fully versed in adjusting new bumpers?

It wouldn't hurt to do a little tutorial on that.

Some time ago you showed photos you took with an endoscope on correct alignment.

[Fireinthebones]

What kind of rubber is being used for the bumpers? Most modern rubbers are pretty impervious to chemical degradation.

I believe they are just stock Bach Bumpers but they might have been replaced sometime

[boneagain]

This is the link to the thread (mentioned by Tim above) with photos of what the bumpers are supposed to achieve:
https://trombonechat.com/viewtopic.php?p=189479#p189479

and here's a link about the tricky business of getting alignment:
https://trombonechat.com/viewtopic.php?f=13&t=27035

You will see the term "witness marks" in the second link. The should be TWO sets under the threaded cap of your valve. One set indicates when the valve bearing has been set into its "reference" position in the valve shell. If this is not dead on the other mark is meaningless.

The second set of marks cross the bearing surfaces between the rotor axle and the actual bearing hole. IF the first set of marks is correct, then a SINGLE mark on the bearing hole should line up in TWO positions: valve open, and valve closed.

The diameter of the valve axis is relatively small. It is EASY to make those marks a few degrees off and not be easy to notice.

That is where a borescope comes in. I had EXCELLENT alignments from techs before borescopes were generally available. I get that alignment much more easily now. And my favorite tech (at over 90 years old) makes regular use of one.

The reason is simple leverage. The visibility of misalignment increases proportionally to the diameter of the place of measurement. If the valve axle diameter is 1/4" and the valve diameter is 1", then it will be four times easier to see a misalignment at the outer circumference of the valve.

As noted in the second thread, most of the corrections are done by shaving the bumper.

Other things to keep in mind that I don't recall from the thread:

1) bumpers may "settle in." This was VERY true in the good ol' cork days. Depending on the synthetic it can still be true. If you cut JUST right on the first pass and the bumpers settle in, you'll need to put in new ones after they settle. I've seen a couple shop tricks that avoid this, but lack the skill to do those tricks.

2) bumpers DO harden. They have to be, to some degree, compliant. Compliance usually implies some kind of volatility. That being said, I have some very old neoprene and buna seals that still work fine. But some rubbers will suck up your valve oil and find interesting and unpleasant ways to decompose. The stuff from the music supply houses is time-tested to behave.

So, maybe order more than one set? Keep spares in your case for WHEN you lose one someday? Watch your teacher carefully to learn the technique?

Enjoy the learning experience!

[boneagain]

Oh: back to original question: from all you've posted about these I doubt there is anything you could have done to retard the self-destruct mechanism on the bumpers

Best to consider them slightly less consumable than slide cream, learn to apply, and get back to those long tones!

[Bonearzt]

I NEVER rely on the witness marks on the rotor and back bearing!!
ALWAYS sight through the slide receiver for the F valve and the end of the gooseneck for the Gb valve!!!

[timothy42b]

I NEVER rely on the witness marks on the rotor and back bearing!!
ALWAYS sight through the slide receiver for the F valve and the end of the gooseneck for the Gb valve!!!

I hadn't thought of doing that though it's obviously a good idea.

I've been playing straight tenor for a bit because of some joint aches but I got out the 42B and tried this.

Recently I played my brother's Yamaha and had trouble getting a tone, and blamed myself since I've had some chop troubles plus a doctor ordered 3 week layoff, but it turned out the pressure of my thumb was slightly activating that trigger, enough to make it all but unplayable, so I have a new appreciation for that alignment.

Anyway, what I found with my Bach by looking through it was that the no trigger position is slightly past where it just aligns. (I watch the hole get bigger as I slowly release the valve, and it moves past the completely clear point.) Is there some safety factor there? That implies the cork on that side is worn down or compressed and the valve opens too far.

But without Dave's borescope I don't know how I could see the position with the trigger fully depressed. But I pushed the tuning slide all the way in, and could hear a hiss as air got past it. There is still a pop when I release, so it isn't a big leak, but it sounds like maybe that cork is too high?

Anyway, I've assumed all my difficulties in low range are my own fault, and that's probably true, but the horn may be contributing.

[Bonearzt]

I NEVER rely on the witness marks on the rotor and back bearing!!
ALWAYS sight through the slide receiver for the F valve and the end of the gooseneck for the Gb valve!!!

Anyway, what I found with my Bach by looking through it was that the no trigger position is slightly past where it just aligns. (I watch the hole get bigger as I slowly release the valve, and it moves past the completely clear point.) Is there some safety factor there? That implies the cork on that side is worn down or compressed and the valve opens too far.

But without Dave's borescope I don't know how I could see the position with the trigger fully depressed. But I pushed the tuning slide all the way in, and could hear a hiss as air got past it. There is still a pop when I release, so it isn't a big leak, but it sounds like maybe that cork is too high?

Anyway, I've assumed all my difficulties in low range are my own fault, and that's probably true, but the horn may be contributing.

The only "safety" factor I might allow is a slight bit of extra material on the trigger depression stroke as you usually press more than necessary.

Looking through both the receiver and tuning slide ends should give you enough of a view to align the bumpers correctly on both F and Gb valves.
Fortunately on Bachs, there is enough room in the screw holes on the stop plate to move it around to align without having to slice the bumpers.