hollow rotors

[bloke]

Who here has one of those Czech tubas from around 35 or 40 years ago with those super light hollow rotary valves?

Aside from possible linkage noise (if your linkage possibly needs attention these days), how is the touch?

We've all seen the plastic sandwich rotors, but actually building a rotary valve out of a central stem, a couple of Lathe turned discs extending from that central stem, and everything else being a tapered tube and inserted contoured tubing trimmed off at the surface.. to me that's quite an impressive feat...

...ie. anytime machine work is combined with assembly (brazing or welding) work, etc.

I'm also impressed when anyone goes to the trouble to figure out what the least amount of mass is necessary to make something be everything it needs to be.

[peteedwards]

I am starting up a service making & fitting 3d printed (brass or stainless steel) replacement rotors, with optimized duct geometry (no internal sharp corners or nooks & crannies) and super lightweight. This translates to low rotational inertia, faster action and less bounce on the return stroke. My bass trombone rotors are less than 23g compared to the original "traditional" machined rotor of 51g. I can imagine this would be of benefit to tuba rotors, even more so than trombones, no?
Not fancy brazing etc, but a cool use of new technology.

3Dprinted rotor.png (73.55 KiB) Viewed 1453 times

Without going into too much detail, here is the link to my thread on Trombone Chat.
https://www.trombonechat.com/viewtopic.php?t=36910

[MiBrassFS]

I’ve never dissected one of these valves, but I always thought of them as built similarly to piston valves in that they’re a main body tube with intersecting tubes. The axle, bearing surfaces, and tapers definitely add levels of complication.

For people who haven’t seen such a process, in this thread there’s a link to a show where they make a piston. A bunch of steps aren’t shown for the sake of brevity, tv…, but it does show the basics. viewtopic.php?t=9859

[arpthark]

I wonder if my 80s Piggy has these. How do I check? See if they float?

[peteedwards]

Of course, to facilitate slide pulling there would need to be a tiny vent hole, lining up with a hole in the casing.

venthole.png (76 KiB) Viewed 1362 times

[bloke]

I think those valves are a great idea for reducing contact surface and weight, but also (and please don't take offense, because I don't mean any) I think it's wonderful that the first response is about a valve that is not a hollow valve. This is right in keeping.
Of course, the material between the two round holes defines even a smaller bore than the bore feeding into the rotors, rather than closer to the same bore, as far as area is concerned. If as much of that is cut away as possible, the bore through the rotors will be larger and the amount of contact area will be less.

============

To tell whether a regular Czech rotary valve is hollow, I think the thing to do would be to check for soldering/brazing lines, as well as feeling it in your hand.

[arpthark]

I actually haven't taken my Piggy apart and looked at the innards yet since I got it in March. Next time I do I'll have to see.

[LeMark]

I dont think a cerveny from the 80's will have hollow valves. I dont think my big 601 from the 60's has them

[bloke]

My guess is early '90s or so.

[peteedwards]

I'm also impressed when anyone goes to the trouble to figure out what the least amount of mass is necessary to make something be everything it needs to be.

If the goal is reduced mass, then "hollow" isn't necessarily the point, right?

Of course, the material between the two round holes defines even a smaller bore than the bore feeding into the rotors, rather than closer to the same bore, as far as area is concerned. If as much of that is cut away as possible, the bore through the rotors will be larger and the amount of contact area will be less.

That is assuming the bores are round, which they are not. The cross sectional area remains constant throughout. It is similar to the concept of the CAIDEX valve, but mine is not elliptical.

[bloke]

If a rotor is less than 2X the bore in diameter, it's impossible for the bore through the rotor to be both round and the same diameter as the round tubing feeding into it... unless it goes into another dimension, as the K valve (that Bach used for a short time) did.

I pointed out something that's true, but I don't want to criticize your rotor, because I can't build it and you can and you did.

[peteedwards]

I have found it is more important that the sound path be smooth and continuous than it be round. It can effectively have the same tube diameter & fit into the smaller overall diameter. Yes it is not round, but eliminating the sharp edges, corners, and nooks & crannies makes all the difference.

[bloke]

Okay. That may or may not be the most important thing, but at least we agree on the thing that about which I thought we originally disagreed.

Taking away that span between those two round holes would smooth things out though, would it not?

With the rotorvcasing defining an (albeit simple) convex shape, it seems to me that is smoother than that span (between the two round holes) creating a more concave shape. I would predict that there would be a pretty easy thing to change in your printing program, though - as I've already admitted - I'm completely ignorant regarding 3D printing.

I've seen pictures of your valve before and I think it would be fascinating to try one out, but my understanding is that the only way to fit them to an existing casing is the same way that I fit replacement rotors to existing casings, and that method defines that - if I don't like the aftermarket rotor - the original one will no longer fit.

Otherwise of course replacing the entire valve assembly makes complete sense for a test, but it's a lot of take apart and sometimes an instrument is really pretty - finish-wise - prior to such experiments.

Specifically, my instrument features five rotors that are all the same very large bore size, but the design engineers decided that making the fourth valve one extra large in diameter would improve air flow through the fourth valve circuit. Being one who is not particularly sure whether resistance, lack of resistance, or some sort of resistance balance is the most beneficial, about all I truly notice - with that extra large diameter valve - is that it is very subtly slower than the others (due to the extra surface area and mass). If I was extra picky, I might replace it with a rotor assembly just like the other four, but the complication is that I would throw off the build geometry of the instrument by probably ten or more millimeters, and that would define a mess. Truth be told, the other four are quite fast, because they are the same rotor body that the same manufacturer uses for a smaller bore rotor, and - having been cut out to the larger bore - makes them weigh less, and have less contact area on their surfaces... faster and lighter, obviously, than for the model that size rotor is usually used.

[the elephant]

I have found it is more important that the sound path be smooth and continuous than it be round. It can effectively have the same tube diameter & fit into the smaller overall diameter. Yes it is not round, but eliminating the sharp edges, corners, and nooks & crannies makes all the difference.

That is the same idea behind porting an intake manifold on a car's engine…

• the shape is less of a factor, so long as volume is the same
• the path is as smooth as possible
• all obstructions or sharp edges are removed.

I like this idea very much. Let me know if you need a quality tuba to experiment with for a while. I'd be happy to have some of your valves to test out after you are done with it.

By the way — how've you been, @peteedwards? It's been a long time…

[peteedwards]

I'm doing well, Wade!
Somehow I lost your email & it took me a while to find you here...PM me & we'll catch up.
Yes its similar concept to intake & especially exhaust manifolds, its not necessarily about air flow as optimizing for resonance.
In an analogy to electricity, air flow is DC, resonance is AC. The standing wave inside a tuba is AC. It is a shock wave moving back & forth rapidly between the mouthpiece & the bell. Much more rapidly than the flow of air from the lungs. (It propagates at the speed of sound)

Here's a cross section of a "normal" rotary valve on left and "optimized" on the right.

cross section.png (20.66 KiB) Viewed 1136 times

you can see where incorporating the casing ID into the path creates two very sharp turns in the path, effectively setting up a mini Helmholtz chamber inside the valve. This leads to wolf tones, inconsistent tone harmonic structure, poor slotting, etc.
Its even ore evident when you look at the path in a 3D view:

sharp edges.png (9.02 KiB) Viewed 1136 times

[peteedwards]

my understanding is that the only way to fit them to an existing casing is the same way that I fit replacement rotors to existing casings, and that method defines that - if I don't like the aftermarket rotor - the original one will no longer fit.

This is not the case with the method I am using (I don't alter the casing), and I am currently developing a method to make the fitting process even easier, wear far less over time, and make future repairs/refurbishments more straightforward & easy.

[bloke]

That sounds really encouraging!

[Oedipoes]

With hollow rotor construction you mean like these that Dan Oberloh made?

http://www.oberloh.com/gallery/rotaryva ... onpage.htm

[bloke]

Not having been scientifically shown how any of the design "this" necessarily leads to any of the acoustical "that", (given a choice) I'd personally choose your minimized rotor body design, yet with the porting displayed on the left. Having spent time in a shop with one of the world's leading bassoon repair/customizing people, I'm completely aware of the "smooth edges" theory - regarding wind instruments, but I've never seen that (whatever effects smooth vs. sharp edges offer) the effect of neither has been scientifically measured (and only with players claiming a perceived improvement (and not even A/B comparisons, as - once B is done, A is no longer available). Also - having had countless rotor assemblies apart over the last half century, The "points" shown in the diagram on the left are almost never points, but are nearly always fashioned as to be rounded.

That having been said...
Whether the extra surface material - which takes away space from the rotor body port (and making more of a zig-zig in the bore) has a positive effect, a negative effect, or no effect, I've also wondered about (as I've found that surface contact on rotors affects their resistance to ease of rotation - which some refer to as "speed" - more than anything) whether reducing (as you've done with your printing tack) unnecessary surface contact would help rotor "lightness/speed" more than anything.

I HAVE (decades ago) reduced mass (from sluggish rotors, which were larger in diameter and mass than necessary) and reducing mass - actually - did not help the speed of those rotors in the least. This is why (and referring to your thoughtful-and-very-clever contact area reducing design) I tend to suspect that the contact area "drag" is the main problem, and not-so-much the overall mass/weight.

Hoping that Dan doesn't become annoyed with me stealing/editing one of his pictures, something such as this (whereby an EXISTING rotor could have wedges cut out of it - via laser or via whatever - and (simply) check/address the freshly-cut edges for burrs.

Practically speaking...
Anyone who is seeking lighter/faster rotors ALREADY OWNS a tuba that they would like to mechanically improve (as no one shops for valves first and then - later - a tuba on which to mount them), and (I would estimate) 100% of people would prefer to keep (even if adulterated) their oem rotors - which are already factory fit-and-lapped to the casings.

If these cuts could be made safely (and all that would be involved - after having made the cuts - would possibly be chasing the edges of the cuts (and not even on the tops/bottoms) horizontally with two or three grades of grades of sandpaper (medium, fine, and super-fine) then that - at least to me - seems to be an attractive proposition, whereby the original rotors (which already fit, and already feature porting that works) are both reduced in mass and in contact area.

cut down rotor body.jpg (18.54 KiB) Viewed 799 times

Finally...
I need for you to understand that I'm not criticizing either your amazing efforts nor your design.
- I can't make those.
- You CAN make those.
- I'm a skeptic regarding most things which are unproven (the acoustic claims being the only things to which I don't immediately agree - at least, not to any measurable/noticeable effect).
- I have messed around with mass reduction and (though ALSO non-scientific) was disappointed at a complete lack of noticeable improvement, which tends to encourage me to suspect that contact area is much more important (regarding speed/lightness) than is mass....YET...
- I remember the hollow rotors (on some new/demo 1990's Czech tubas) offering a light touch, but it could have been JUST AS MUCH due to minimum contact area as minimum mass (as - another example) my "regular" B&S F tuba rotors are very fast and do not demand strong springs - whereas those rotors diameters (thus contact area) is minimized in a different way).
- I believe most people would be more inclined to alter existing rotor bodies for some demonstrated benefit, vs. starting over.
- You have prompted me to think about these issues in even more ways. (Thank-you!)

[peteedwards]

You're welcome!
a couple of notes-
-you would never tolerate a dent shaped like that in your leadpipe, correct? why would it be any less bad one inch further down past the end of the leadpipe? or a series of 5 - 12 such dents in a row?
-I can do and have done A/B comparisons, as I make the new valves to fit the existing casings, without altering the casings. You can try the old vs new side-by-side or at least with some disassembly/re-assembly time. If interested in the effect of reduced mass ONLY, I can certainly print skeletonized version of traditional valve port geometry.
-Regarding acoustical claims, I know what I wrote is just words, unscientific, etc. so the only way to find out for sure is to try for yourself. After all, science can only take us so far, we're making art, and art is by definition subjective.
-in your mass reduction experiments were you taking out more than half the mass? My guess is not anywhere near that amount, and probably not enough to really notice a significant change. I guess the real test would be to see how light a return spring the valve will tolerate, and still "keep up" with your fingers.
-You may be correct about the surface area reduction having an effect on reduced friction, I suspect its some combination of mass/rotational inertia reduction and reduced friction.
And lastly I apologize for hijacking the thread