Bumper material for Mackbrass 410CC?

[royjohn]

I bought some 3/16", red silicone O-rings, 70 durometer, for replacement bumpers for my Mackbrass 410 CC,
but I find they are too thin. Apparently what is in the horn was stock that was cut down from something
larger to fit. Does anybody have a source for the proper stock for this?

Meanwhile I have four, 4 inch, 3/16" diameter O-rings which I can't use...if they will fit your horn, PM me
with your postal address and I will send you some...
TIA,
royjohn

[bloke]

Your post offers material (of no use to you) to others, but you ended the caption of your post with a question mark (regarding a source)… so I’m going to answer what I see as another implied question.
=============
My strategy is always to stuff something larger (than those concave round shapes in cork plates) into them, and then to use a very sharp (new) single edge razor blade to trim off the faces of them nice and flat at the correct points. This not only assures that there will be enough material to align the rotors properly, but it also looks “fesshunul”.

Some people claim to be able to stretch whatever larger material they’re using to get it in to those smaller concave shapes, but I don’t have any luck with that. What I do is to use a rounded (worn, and not much use as a screwdriver) screwdriver edge and roll the material into those openings. It takes a bit of teasing/finger strength, and it works much better if you remove the cork plates from the instrument and stick them in vice jaws - protecting them (from being marked up) with cereal-box cardboard.

sidebar: The firmer the material selected for bumpers, the more important it is to for rotors to feature absolutely no vertical play. Firmer bumper material encourages rotors - with N-S play - to click. Some rotors – on some of the more economically-priced instruments - aren’t particularly cooperative, when a re-installer is trying to combine “free-turning“ and “no vertical play“ - which is why quite a few of the more economically-priced rotary instruments are shipped with extremely soft bumper material.

To attempt to answer the question asked, obviously something larger is what you need - regardless of what type of material you choose (whether some fancy-named type of rubber, or *salvaged pencil erasers). You probably just need to use something that’s either a 32nd or a 16th inch larger in diameter, yes?
_________________
*and yes, one time - when I was supposed to quickly repair a school’s rotary tuba (and discovered that I was completely out of bumper material), I ran around the corner to the dollar store, bought ten pencils, peeled the erasers out of eight of them, and used them to replace the bumpers in the tuba - because the school needed it back right away. I got it back (for subsequent repairs) two years later, and those pencil erasers were still holding up OK.

choice of density, here: https://www.mcmaster.com/8466K12/

[Jperry1466]

This is what Tom McGrady told me to get, and it worked fine.

https://www.grainger.com/product/GRAING ... -Std-6RTA9

This seems to be the current Amazon version:

https://www.amazon.com/CleverDelights-B ... 178&sr=8-3

[royjohn]

Hi Jperry,
Thanks for the recommendation of the 3/16" rubber...that's what I'd seen recommended before and that's
basically what I bought, and while it fit the notches fine, it just wasn't long enough to match up the witness
marks on the valves...IDK if that has something to do with the modifications to the valves of this horn...
this is the elephant's horn, which he retrofitted with sturdier ball and socket linkages several years ago.
I can't see why this would make a difference, but some of the bumpers need to be longer than 3/16".
I did email Chris at Mack Brass and he suggested just getting something bigger and cutting it down to fit,
which is what I'll do. I only needed two longer bumpers, and I was able to make those out of pencil erasers.
Chris also suggested neoprene for the down stroke and cork for the upstroke, so I'll look for some cork
material to cut down eventually, too.
Best,
royjohn

[the elephant]

As Joe told you, you are supposed to use a material that is of a larger diameter, pinch it into the cork plate holders, and then use a single edge razor blade (a shop knife) to trim the material so that the marks are met. Do not ever use a material that is of the same diameter as the cork plate "keepers".

1.) It will fall out at inopportune moments. It must be in the keepers very tightly.

2.). it will never make be fat enough unless it is bulging out of the "keepers". This is by design.

And no, the relationship between the location of the stop arm when hitting one of the two alignment marks correctly and the OD of the selected bumper material is not affected by the type of linkage used. They are mutually exclusive.

What is wrong with the material I used? It is from Miraphone and of the highest quality you can use. It is genuine neoprene and not Buna N or mushy silicone. It is a bumper, not a pillow. If it is too soft the valves will never line up correctly as they can over-rotate when pressed, and you do not want them to bounce or your slurred technique will never be smooth and unbroken.

If you are worried about them making noise you can attenuate this somewhat by using (or mixing) various oils. The Jinbao rotors make noise. They will always make some noise, even after someone like me spends six hours cleaning them up, so to speak.

What do you dislike about the neoprene I installed? It is the material used on all the nicer Euro-made rotors. It is never used on Chinese rotors, which almost always come with squishy, quick-to-deteriorate silicone, which needs to be replaced as soon as a person gets a new horn from over there.

Remember that you need to compress the bumper material so that it is a nearly flat oval, slip it into the keepers, allow it to expand, then trim it to fit. Those valves are inaccurate enough that you need to trim each bumper to fit. The cork plates do not fit uniformly enough from valve to valve to allow you to simply install one size of bumper without custom trimming them, and then swap the cork plates; each cork plate, once the bumpers have been trimmed, need to stay with that casing — don't mix them up!

If you try for a uniform, neat-looking untrimmed bumper it is not possible to have AND have proper valve alignment. It is like setting valve lash on a car. Each one has to be adjusted to itself. If it were otherwise then you could just adjust them all the same and call it done. But if you do that the engine will not run smoothly. The bumpers on a rotary valve are the one adjustment point so they should NOT all match.

Best of luck!

[bloke]

About the only exceptions I’ve ever seen - to the scenario outlined by Wade - are those high-priced student Yamaha rotary tubas - mostly bought by schools.

They are factory fitted with round bumpers that that just fit into the cork plate cups (no rolling, compressing, nor stretching required), and seem to line up just so when the stop arms strike against the untrimmed tangents of those round bumpers…

… and those instruments do tend to show up in my shop missing a bumper or two, due to the fact that the bumpers are not wedged into the court plates. About the only other examples of this that comes to mind are those dubious cone-shaped trombone F-attachment valves, whereby the stock bumpers just lay into the cork plate cups, and are not tightly fit.

Wade has accurately described the instruments to what he refers - mostly towards the last half of his post. Not only does the screw alignment - in regards to mounting the cork plates - seem to be “by eye” (dubious), but the alignment marks on the bottom stems of the rotors seem to be “by eye” as well.

The make up and hardness of bumpers is up for debate, and -,when getting really picky - different materials might be best for different people or different instruments. As I have admitted, I went around the corner and bought a handful of pencils - to tear out the erasers - for an emergency re-corking of a school’s rotary, when I found that I had allowed myself to run out of material… They felt fine, and they lasted a good while (years, without significant deterioration). Though I have not used pencil erasers before nor since, I would rate pencil erasers five-to-one over the silicone-looking stuff that is installed on the least expensive Asian imports. The closer to perfect the construction of a rotor, the harder the material (nearly eliminating bumper material compression and alignment anomalies during playing) can be used without encouraging a clicking or rattling noise, but - as tubas are so large and are also acoustical amplifiers - that factor has to be taken into consideration as well.
I recall “Mirafone” tubas - specifically from several decades ago - having a tendency for their valves to bounce with factory bumpers, and – at a show - I pointed out to their (then) USA importer that they were screwing down the cork plates to the instruments prior to lacquering them, and their bumpers featured a coating of hard epoxy lacquer. Once they altered this procedure, the bouncing problem seemed to stop - with their factory bumper material.

My Soviet-satellite-era East German tuba features very small diameter bumpers. I use particularly hard material on that instrument, and neither do the rotors bounce nor are they loud. Though it is an F tuba, it is not particularly small, so there is just as much potential to amplify the sound of the impact as with many other tubas.

[royjohn]

My, my,,, it seems a little tempest in a teapot is brewing.

Here's my take...after several months of playing this 410 I bought from the elephant, I went to lube the rotor shafts and noticed that when I took off the back plates that some of the valves were off their witness marks. I bought some 3/16" neoprene of 70 dur and it fit, when compressed, into the plate notches. However, it wasn't tall enough to adjust the valves to the witness marks. So I got some add-on pencil erasers and made a few new bumpers until I could find a better source...I only needed two or three because I could use the material on the horn by switching some bumpers out. And, yes, I had the brains to trim the bumpers to fit with a razor knife, thanks.

I lined up the bumpers on the valves and all is relatively fine. One bumper, when short enough, allows one of the ball and socket links to hit the rotor shaft, so I'll have to work on that, but otherwise, things are OK. I am aware that Jim Bao valves make some noise and I sleep OK despite this small trial.

Wade, I had no problem with the material you used, but after some use, a couple or three of the valves were off their witness marks, so I adjusted them. If the witness marks are not accurate, IDK what exactly to do about that. If you or bloke espouse this view, maybe you can advise.

I consider myself lucky to have this very nice horn and play it as much as I can.
Best,
royjohn

[Worth]

Sitting on the sidelines, this discussion is of interest to me as I own a couple rotor tubas. This is a slight hijack as the question relates to the marks themselves, and not the bumper material or technique of replacing the bumpers. Since the marks are under discussion I figure it belongs here.

Is perfect the enemy of good? Or restated, how OCD should we be about perfect alignment of these marks and what playing handicap might a very slight misalignment of marks produce (i.e. off 1 mm on valve closing or downstroke)? Additionally, how exact are the marks themselves on German tubas, on Chinese tubas, on Czech tubas etc. etc. and can we rely on their precision? Is a boroscope the only true way to adjust bumper volume? How perfect does it all really have to be?

[bloke]

It’s probably because I’m a crappy player, but I don’t notice until rotor or piston alignment starts to get fairly bad. Brass musicians seem to put a lot of stock in “flow“, but the playing characteristics of these instruments have little to do with that…a “little”? sure, so it’s certainly worth optimizing, but the design of tuba rotors defines that the bore is extremely pinched going through them, anyway.

I’m not sure how to address a question like, “Which countries’ tubas are always perfectly marked, and which countries’ tubas are never perfectly marked?”

With rotary tubas that feature vertical main tuning slides, it’s often possible to check up through the valves (to confirm good alignment, when factory marks are considered to be suspect) with a pair of reading glasses and a phone light.
Second valve rotors can always be visually inspected, and there are other ways to line up rotors, such as matching the stop arm angles to that of the #2 stop arm, once it is aligned. Something that works surprisingly well is to play a middle range pitch while rotating a rotor extremely slowly. The sound will tell when it is the worst on either side (just begins to leak), so precisely halfway between those two points is going to be the best.

I usually make the bumpers - on the side against which the stop arms are slammed on the downstroke - a little bit too thick.

I’m sort of lazy looking after my own instruments versus taking care of others’, because no one pays me to look after my own. Behind one of the rotor bumpers on my F tuba, I believe there’s still to this day a little 1/4” tall piece of paper clip that I jammed in there at a rehearsal, because I noticed that it was worn down too far. When I get home, I never think of replacing it. How much better do you think it would play - were I to replace that bumper - since the one that’s in there now offers perfect alignment?

I very generously oil my valves on whatever tuba I’m going to play - prior to playing it. I suspect this helps them stay cleaner than some others’, as well as keeping my valve tolerances really close to like new. Over and over, I’ve seen threads and posts about some X brand of valve oil being wonderful, because it lasts for a week or etc. I don’t believe that’s the point of using valve oil.

[DonO.]

Back in the dark ages, when I bought my first “good” horn, a used Meinl-Weston 25, the bumpers were cork. I played it that way for a while but the cork quickly began to deteriorate. I acquired some neoprene rod material. I can’t remember how I was lucky enough to find the right size. I think I just went to a music store with a repair shop and told them what I wanted and what it was for, and they sold me a foot or so. Hardest part was picking out all the cork and the little bits it left behind. The neoprene went right in with a little compression, trimmed with a razor blade, and they worked a charm right out of the box. The indicator marks all lined up beautifully with no adjustment. I was just lucky I guess. Same thing when I switched to a Cerveny made Amati. That horn I bought brand new, and its bumper material was the clear stuff. It did not last, got all chewed up and pieces of it started falling out. I still had some of that neoprene left, so I did the same job on the Amati. Again, no problems, everything lined right up, easy peasy. I no longer have a rotary horn, so no dog in this race, but in my experience neoprene is the way to go. Maybe there is something about the designs of some tubas that complicates things. But in my experience it just wasn’t a big deal on those two.

[bloke]

It just so happened that the tangential points - on that diameter of neoprene that you were sold - happened to be at the right point for good alignment, but again: The only manufacturer (of which I’m aware) that ships out rotor bumpers set up that way is Yamaha, and Yamaha‘s strategy - in my experience - causes problems.

[the elephant]

There was a small amount of slop in the cork plates of that tuba, IIRC. The plates may have shifted a small amount. Other than that, without seeing it I have no idea.

How far off the marks are we talking, here? An amount that matters, or an amount where there is no visible "blade" of rotor wall showing? Rotors from most makers have a small zone where they can be adjusted and be fine. I have noted that some makers will stamp the marks with the rotor turned a degree or two on either side of "perfect" right next to another one that is stamped to be set turned in the other direction. These are not piston valves, where two circles must align perfectly.

[bloke]

Cork and fake silicone don’t last very long.

Cylindrical material - that slips easily into the cups of cork plates - can also slip out easily.

Whether rotor alignment is pretty good, very good, or extremely good, all of those are good.

Harder/denser bumper material will tend to encourage clicky valves to click more.

It takes a considerable amount of wrong to make a good tuba play badly, but that quantity of wrong can be achieved.

[royjohn]

I don't know why this is an issue for anyone else but me, but since the question was asked, my rotors were about 30 minutes to 90 minutes off on an hour hand, or about 15 to 45 degrees off. I thought that that was enough to make it an issue. I am glad to hear that it isn't too critical (which I would take to mean plus or minus 10 degrees), because, as I mentioned, one of my valves has to be set so that the ball and socket arm hits the rotor shaft on the downstroke, producing a "clank" and it may be that if I make the bumper a little "taller" it won't clank and will not be off enough to matter.

I noticed that some of the top plates, which are secured with little screws, are a little loose, so I'm going to tighten those up, too, and maybe that will make some difference in noise or alignment.

Thanks to all who have responded thus far...you learn something new every day...

-royjohn

[bloke]

one of my valves has to be set so that the ball and socket arm hits the rotor shaft on the downstroke, producing a "clank" and it may be that if I make the bumper a little "taller" it won't clank and will not be off enough to matter.

Consider putting a small horizontal angle in the action arms - perhaps (let your own visual scrutiny be your guide) 3/8" back from (??) the stop-arm links.

That should offer the clearance desired as - likely - if one is actually hitting against the center spindle of the stop-arm, (or or more of) the others is/are coming damn close to doing the same thing.

No one should have to keep enough thickness bumper material on-board (overriding the primary purpose of "rotor alignment") simply to prevent the action arms from striking the stop-arm center spindles.

[Jperry1466]

Hi Jperry,
Thanks for the recommendation of the 3/16" rubber...that's what I'd seen recommended before and that's
basically what I bought, and while it fit the notches fine, it just wasn't long enough to match up the witness
marks on the valves...
Best,
royjohn

Interesting thing about the Mack witness marks: I took mine into the shop and asked the repairman (also a tuba player) to go through the tuba thoroughly. He used a USB endoscope attached to his phone camera to line the tubing up internally with the rotors, then trimmed the rubber cord. When he was done, I looked at the back of the valves, and while some of the witness marks lined up, others were as much as 1/16" off. It did play better, so the problem was in the machining done at the factory. I took pictures of each valve and go by that now when replacing the bumpers. Example below is correctly aligned internally.

[bloke]

[Three Valves]

I noticed that some of the top plates, which are secured with little screws, are a little loose, so I'm going to tighten those up, too, and maybe that will make some difference in noise or alignment.

It should. It cured the issue I was having with by Mack 210. I used Loktite to prevent them from backing out again. (Do not use the permanent variety)

[LibraryMark]

One bumper, when short enough, allows one of the ball and socket links to hit the rotor shaft, so I'll have to work on that, but otherwise, things are OK. I am aware that Jim Bao valves make some noise and I sleep OK despite this small trial.

On my 410 I had to put the ball joint on the other side of the paddle arm on a couple valves to keep the rotor ball joint from hitting the shaft. Shortly after I bought the thing I contacted Tom McGrady about buying some spare parts to try to rework the linkages to address these problems but he did not respond. Tom - If you are listening, I could still use some help.

[Three Valves]

Shortly after I bought the thing I contacted Tom McGrady about buying some spare parts to try to rework the linkages to address these problems but he did not respond. Tom - If you are listening, I could still use some help.

Call, don't email.