Rath R9 bumper size

[vetsurginc]

Need to replace rotor bumpers on my 2009 Rath bass. Measures 3.3 mm but it has been in the socket for a long time.

Any suggestions?

Thanks for tips!

[Blabberbucket]

Bumpers are typically not a "drop-in" replacement and usually need to be trimmed to proper alignment.

If you are having them replaced because your rotors are noisy, there are likely also fit issues with your valve bearings and levers.

[brassmedic]

Can't you buy them from Rath?

[Sesquitone]

Bumpers are typically not a "drop-in" replacement and usually need to be trimmed to proper alignment.

Don't trim! You can easily "over-trim"; then you have to start again (after suitable cursing).
Instead, use individually adjustable stops. Standard stop cradles are easily modified. See below.


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[ZacharyThornton]

^ the older rotax valves were not adjustable like that.
I would reach out to Rath and buy the ones they use. Also, trim them down or have your tech do it. You would be stunned how much just a little bit off a bumper can help your sound.

[vetsurginc]

It's the resting position on the F valve that is allowing the valve rotor to sit about one quarter closed. Dillon Music is the importer for Rath on the east coast. But I've had no luck getting an answer from them, even with calls and emails. Rath really wants you to deal with them. No answer from Tim. I do have material coming from Osmuns (soon I hope).

The local tech who I trust cannot take it in before April. Fortunately I have another bass I can use in the interim. But it doesn't have the Rath sound that I like for symphonic work.

I would love it if Rath had the adjustible bumpers. I love their socket design - no threads, simple clamp, very secure.

Normally I would be happy for the tech to do the work. I'm just frustrated by the delay.

Thanks for all your thoughts!!!

[Sesquitone]

^ the older rotax valves were not adjustable like that.
I would reach out to Rath and buy the ones they use. Also, trim them down or have your tech do it. You would be stunned how much just a little bit off a bumper can help your sound.

That's correct. But the Rotax and (most) other bumper-stop one-piece cradles are easily modified to make an individually adjustable pair. This is a do-it-yourself project. You'll need a fine-toothed hacksaw, a small rat-tail file and a fine flat file. And an appropriately sized hex key (Allen wrench).
(i) remove the one-piece cradle and cut out a small 'wedge' from the centre.
(ii) elongate the machine-bolt holes (along an arc, in both directions) with the rat-tail file.
(iii) round off and smooth-up all sharp corners and replace.
(iv) use full-sized cork (or Neoprene, . . .) bumpers.
(v) with the machine bolts slightly tightened, adjust each side until both witness marks (or other diagnostics) are precisely aligned.
(vi) tighten the machine bolts very tight.
[Ideally, there should be a ring (or equivalent) around the two-piece cradle (to hedge against loosening). A friendly tech can probably solder something onto the casing to approximate the ring in the picture previously shown.]

And, yes, even a very slight misalignment can cause major problems with any valve.

Do not trim! That's way too 'approximate'--and way too frustrating!!!

Good luck!

[ZacharyThornton]

I would say that is a do it yourself project for very few players.

[ithinknot]

^ ...and speaking as someone who could comfortably do either, the suggestion that it's less trouble than trimming bumpers is quite amusing. Share your woes with a double reed player; you'll give them a good laugh.

(I get it; to the pure engineering brain, these solutions are irresistible. But apart from the added manufacturing cost, it's also a standing invitation to ham-fisted end users to overtighten, shear screw heads, or strip the threading from the valve casing, which remains very soft from port brazing... There's genuine value in leaving certain things just difficult enough to put the wrong sort of people off.)

Anyway, if you can't wait, then get your tech to give you some 4mm nitrile or silicone rubber cord, 70 durometer give or take - or get your own - and do it yourself.

[Sesquitone]

I would love it if Rath had the adjustible bumpers. I love their socket design - no threads, simple clamp, very secure.
Thanks for all your thoughts!!!

The reason for the butt joint inside the slide receiver of Rath trombones is to eliminate any possibility of a gap between the end of the incoming slide tube and the beginning of the valve knuckle—that often occurs inside more conventional slide receivers. The (oversized-bore) 'chamber' that may occur inside the receiver in those cases acts as a little Helmholtz resonator that (sometimes) causes wolf tones at particular frequencies. The Rath slide joint should always be pulled in tight—it should not be used as a 'tuning slide'!

And, by the way, the adjustable-bumper 'fix' is a very easy DIY project. You only need to do the metal cutting and slotting once (and, of course, you could always have your tech do it). Then future adjustments only require loosening and (carefully) retightening the two machine bolts. And let me emphasise, again, the importance of having extremely precise alignment—at both ends of the angular throw of the rotor. Tiny misalignment causes reflections off the little discontinuities in the sound-path between the valve knuckles and the rotor ports; and this can affect some frequencies of the overtone structure, leading to a decrement in tone quality. Of course, large misalignments will cause a leak in the acoustic pathway, leading to a 'fuzzy' tone or a complete breakdown. Messing around with an X-Acto knife is a recipe for misaligned rotors (not to mention an increase in one's cursing vocabulary).

[vetsurginc]

'fuzzy' tone or a complete breakdown. Yup that's what I was starting to get. Poor ol' bumper is well and truly worn.

Wish I had a tech within range that wasn't booked to the max. It's good for them, but leaves me with a long wait. Oh well, I knew there was a reason I had 8 bones in the house

[Sesquitone]

'fuzzy' tone or a complete breakdown. Yup that's what I was starting to get. Poor ol' bumper is well and truly worn.

As a temporary fix you might try gluing a small piece of cardboard (or other suitable material) behind the stock bumper material (to push it further out)--and then proceed with conventional razor-trimming. But you've got to get those witness marks 'spot on'. Or cannibalise from one of the other instruments you're not using (trimmed to fit the Rath).

The whole point about individually adjustable stops is that razor-trimming is only in one direction; over-trimming means starting over. Trim (blind)-then-check. Not enough? Trim (blind)-then-check. &c., &c. Oh no! Trimmed too much off! Start over (and hope for the best this time).

With individual stops and slotted bolt-holes, you can adjust in both directions—and check the alignment by eye as you're doing it.

[ithinknot]

Yes, as an emergency measure, shimming is an option, though it might prove easier to sacrifice a wine bottle cork and make a complete bumper rather than dealing with more than one part. Hardware store O-rings might also be quite accessible as material if time is tight.

It's worth noting that your final alignment adjustments should be relative to lever spring tension in the resting position, and a representative degree of thumb pressure when engaged. (This is true in either method, but would be particularly relevant if you chose to float the movable cradles into position with the linkage disconnected.) Unless you're using extremely hard bumper material, these positions aren't necessarily going to perfectly match the results you got with the valve sitting loosely in place with the linkage disengaged, or with the spindle held with inconsistent finger pressure.

There's also the option to use a softer/quieter material in the resting position, where spring tension is essentially constant, and a less compressible material in the engaged position to be more tolerant of user variability.

Just out of interest, I'm sure the spindle/bearing witness marks on the CAIDEX are more trustworthy than some traditional rotors, but is the bearing plate mechanically indexed to the casing, or is that relationship still floating/witnessed in the usual fashion? (Of course, it's easy to use a scope regardless.)

[Sesquitone]

Yes, as an emergency measure, shimming is an option, though it might prove easier to sacrifice a wine bottle cork and make a complete bumper rather than dealing with more than one part. Hardware store O-rings might also be quite accessible as material if time is tight.


There's also the option to use a softer/quieter material in the resting position, where spring tension is essentially constant, and a less compressible material in the engaged position to be more tolerant of user variability.

Just out of interest, I'm sure the spindle/bearing witness marks on the CAIDEX are more trustworthy than some traditional rotors, but is the bearing plate mechanically indexed to the casing, or is that relationship still floating/witnessed in the usual fashion? (Of course, it's easy to use a scope regardless.)

Yes, I forgot about the wine-bottle cork; that's a good idea. And it's a bit easier if you disconnect the linkage—failing that, use a rubber band to hold the toggle arm in the 'active' position against the spring tension.

With the CAIDEX, because of the lipped tubes, there's less margin for error than with traditional (sculpted butterfly) rotaries—only about 12º rotation off bumper (in either direction) before you lose the seal completely. So, yes, we do go to some extra care to make sure the bearing plate is precisely indexed to the casing and that the witness marks do indeed correspond to the correct respective end-points of the rotor throw. Which you can then see, at a glance, through the transparent dome on the end-cap.

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[Blabberbucket]

Bumpers are typically not a "drop-in" replacement and usually need to be trimmed to proper alignment.

Don't trim! You can easily "over-trim"; then you have to start again (after suitable cursing).
Instead, use individually adjustable stops. Standard stop cradles are easily modified. See below.

I agree that your design is superior, allowing precise adjustments without the hassle of trimming bumper material. With all due respect, most players will not invest in a setup like you've shown here unless the horn comes with it installed.

I am not suggesting players install and trim their own bumpers. A good technician will be able to comfortably replace and adjust bumpers, accounting for whatever compression may take place in the material over time, to align a valve properly. 12 degrees of misalignment, which would cause one of your valves to leak, is a rather severe misalignment. I suspect that even the most under-qualified of technicians would not pass an instrument that severely misaligned.

[Sesquitone]

With all due respect, most players will not invest in a setup like you've shown here unless the horn comes with it installed.

Since the original post concerns a Rotax valve on the Rath instrument, I should point out that the adjustable stops and both end-caps (and, for that matter, the rotor) of the CAIDEX valve are compatible with, and can be installed on any (trombone) Rotax valve (of any vintage). I am currently checking to see if we can provide a "kit" that can replace the old Rotax bumper-stops/end-caps with the adjustable-stops arrangement. [The adjustable stops require the new end-cap, which acts as a surrounding 'ring' to guarantee that no loosening occurs. And the other end-cap has the 'see-through' dome.] If so, I will post information here—and in a separate thread (for other Rotax users). Since the inserts will then never have to be replaced (or, thankfully, ever 'trimmed'), the 'cost/benefit ratio' should be quite favourable.

[Sesquitone]

12 degrees of misalignment, which would cause one of your valves to leak, is a rather severe misalignment. I suspect that even the most under-qualified of technicians would not pass an instrument that severely misaligned.

I didn't mean to suggest that one of the stops could be that far misaligned. Rather that that's about how far the rotor has to be turned before the seal is blown. On some (sculpted butterfly) rotaries, the rotor can be turned even further before losing the acoustic seal. But, in all cases, even a slight misalignment of the bumpers can cause damage to the tone quality because of reflections off the resulting discontinuities in the sound-path cross-section.

[vetsurginc]

Actually I didn't mention the valve type in the original. These are Hagmann valves that were current in 2009. Getting to them is pretty easy, just trying ot use the correct materials.

Thanks to everyone for all the ideas!

[Sesquitone]

Actually I didn't mention the valve type in the original. These are Hagmann valves that were current in 2009. Getting to them is pretty easy, just trying to use the correct materials.

Thanks to everyone for all the ideas!

Somehow, along the way it appeared that you were talking about a Rotax. Of course, the Hagmann has a totally different geometry--unrelated to the Rotax (or the CAIDEX). So, basically, forget about my suggestions! It would be best to get original parts from René.

[ghmerrill]

I would say that is a do it yourself project for very few players.

Definitely. I like the approach -- in theory. But I don't think I'm a fan of "tighten the machine bolts very tight," when the machine bolt is steel and the plate it's being torqued into is brass (or even if both are brass). Also not a fan of a single bolt (becoming a pivot point -- and so having to be "very tight"). For standard rotary valves (or others resembling them), trimming is not a problem and is neither difficult nor inaccurate. Problems arise mostly in cases of sloppy design or fabrication (as in the case of my Schiller bass trombone). But those can also generally be dealt with pretty easily.

A lot can sometimes be gained in terms of adjustability with standard bumper sockets if you just carefully elongate the screw holes in them to turn them into slots rather than holes (some manufacturers have actually done this for you!). Then you still have two screws holding the bumper bracket on, no single-bolt pivot problem, and tightening to reasonable (rather than "very tight") torque is quite sufficient. Problems can also sometimes be addressed by using oversize bumpers and then shaping/sizing them effectively.

But if I had a high-end instrument, I think I'd prefer the manufacturer to address such issues for me in one way or another. This is another case where you need to be completely comfortable with whatever path you choose. I've been pretty fearless in the case of my own bass trombone -- but the cost of that (delivered to my door) was $580. And I specifically bought that as an experiment and learning exercise. Most people reading this are in a much different situation.

[hornbuilder]

As alluded to by GHMerrill, relying on one screw to hold a bumper plate pretty much guarantees that screw coming loose, right when you don't want it to! Trimming bumper rubbers really is not difficult, and is very precise, if the tech knows what they're doing.

I would strongly advise against modifying a factory bumper plate as suggested above.

[ghmerrill]

To avoid being unfair ... so far as I can see, the particular solution actually pictured avoids the pivoting bumper problem by constraining its movement by an enclosing ring. That also eliminates the need to excessively tighten the screws. But that solution is way beyond the capabilities of the amateur trombone tech (and, I'm pretty confident, beyond the capabilities of many professional techs). Additionally, that very constraint (which solves one problem) in turn makes the stops less adjustable -- making it apparently equivalent to the original single plate configuration.

[Sesquitone]

To avoid being unfair ... so far as I can see, the particular solution actually pictured avoids the pivoting bumper problem by constraining its movement by an enclosing ring. That also eliminates the need to excessively tighten the screws. But that solution is way beyond the capabilities of the amateur trombone tech (and, I'm pretty confident, beyond the capabilities of many professional techs). Additionally, that very constraint (which solves one problem) in turn makes the stops less adjustable -- making it apparently equivalent to the original single plate configuration.

Since it's now apparent that the original post was actually referring to Hagmann valves, discussing bumper stops for conventional rotary-valve geometry is a bit off-topic. But, since alignment in general is a very important consideration, let me address a couple of points that have arisen. Yes, I agree that 'very tight' was a bad choice of words; I was thinking, subconsciously, in relation to 'partially tightened', which is appropriate for holding things in place while making the adjustments by sliding the individual plates along the slotted bolt-holes. And, yes, the constraining ring is an absolute necessity--but it's not so tight that it restricts the sliding motion of the separate plates while adjustments are being made. And you'll notice that in my initial suggestion, I did advocate having a professional tech solder on such a ring.

Some kind of redundancy, like an indexing screw (or a separate set screw) might also be considered (on original equipment). Or even one left-hand-threaded bolt, as is standard on bicycle pedals (and, yes, I know that this will raise even further 'warning' signals!). But the combination of individually adjustable stops with the single bolt each side and the constraining ring (as original equipment) provides a simple, safe, and workable solution to the 'problem' of keeping extremely precise alignment as the bumper material distorts over time.


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[ghmerrill]

But the combination of individually adjustable stops with the single bolt each side and the constraining ring (as original equipment) provides a simple, safe, and workable solution to the 'problem' of keeping extremely precise alignment as the bumper material distorts over time.

Well, that sound like potential patent territory -- if you wanted to endure the pain of going in that direction/expense by yourself, or maybe convince one of the instrument manufacturers to fund it. Alas, there is some prior art, with at least one previously granted patent (2015, by a professional trombonist) for a rotary valve with "independent adjustable stop elements." I haven't dug into the details of that, but it would introduce a stumbling block.

[Sesquitone]

The idea of adjustable stops (on any kind of valve--for musical instruments, or industrial use, or otherwise) is 'obvious' in the language of patents. The geometry of the valve described in US9153216B2 by Simon-Olivier Tétreault is significantly different from conventional rotary valves (hence its patentability). The details of the shapes of adjustable stops will be different for each different valve geometry: standard rotary, axial-flow, three-duct (Hagmann-type), &c., &c. I purposely decided not to patent (any of the unique--and patentable--aspects of) the CAIDEX valve for good reason: I wanted all of the features to be in the Public Domain so that other manufacturers could, if they so desired, adopt them to (in my not-unbiassed opinion) advance the state of the art.


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