Question for the rotory masters...

[bububassboner]

I have a four rotory valve compensating F tuba from Alexander. The horn is about 70 years old and the valves are shot. My grand father and I wanted to make new rotories and were thinking about making them out of stainless steel or hardened aluminum. How would this affect the "action" of the valves? Has anyone tried this?

[Chuck(G)]

Stainless rotaries would be lighter than brass. Just be certain to measure carefully--the top shaft of a rotor isn't straight-sided, but rather has a slight taper.

The coefficient of thermal expansion of stainless is 18.mumble; while that of cartridge brass is about 19, so it's a pretty close match. On the other hand, aluminum is about 23 and you'd have grief in warm weather.

Galvanically, stainless isn't terribly far from yellow brass, so that looks good (some piston valves are stainless-plated)

I'd like to see a design with a replaceable upper oiltite bearing and a lower ball bearing.

You might also consider monel--a bit lighter than brass and very corrosion-resistant. But it's pretty awful to machine.

Stainless can be a bear to machine, but if you've got the tools, I say, have at it!

[Daniel C. Oberloh]

Are you sure you are up to the task? Unless the rotors are completely destroyed, you would do well to make new bearings (top and back) and rebuild the rotors with copper plate and hard nickel plate. This is a more straight forward and proven way to save the valves then trying to reinvent the wheel. Solid stainless will be quite heavy and aluminum will react to the acidic environment of the horn unless hard-anodized correctly but even that will not last very long in a conventional rotor design and will seize up as soon as the base metal is exposed. The cost to rebuild the rotors is not cheap but the idea of making rotors from scratch is most probably going to be quite a bit more. Even if you make new rotors, you will still need to fabricate replacement bearings if the originals are as worn as the many I have been called on to restore. The double rotor design is not an easy fabrication process, if your goal is to restore the instrument to solid playing condition, I can not recommend the rebuild process strong enough. Be selective and find a capable and reliable shop to do the job for you and in the end you should be quite happy with the final results. Still, if you are up to the task of making the parts, make the rotors out of brass and they will work just like new. Good luck.

just throwing in an additional 2¢

Daniel C. Oberloh
Oberloh Woodwind and Brass Works
www.oberloh.com

[bububassboner]

My grand father is a proto-type engineer so he's got the skills/tools to do this job( we have made some NICE stainless steel mouthpeices). Plus he is teaching me how to work all his stuff with these projects so if it does not work oh well but he wants to make all new rotors. What are some things you guys (cough cough Dan Oblerloh) would say to look out for when doing this project? Any weird things we might not catch the first time through?

[Daniel C. Oberloh]

Its a big leap from mouthpiece to rotor valve but what the heck. If your Grandad has the craftsmanship to pull it off, way cool.

You need to realize that your rotors must be lapped into the original worn casings in order to true them (the inside of the casing) up a little. Putting in a new rotor that is the proper fit will help but you will still have leaks between the ports in the casing wall.
The wear is most prominent between ports, this is why build up and lapping coppered rotors, in my opinion, is a better way to go. I will copper plate and lap them in as many as four times before they are ready for nickel. The build up and breaking in trues and fits the cylinder wall of the rotor casing at the same time it is breaking in the fit of the rotor. If you make the rotors you will need to make them oversize and lap them in after the new bearings are installed. Its not just the rotors that are worn out, so is the casing.
Be very careful, it is easy to throw off the geometry and wreck a rotor casing. You only have the one shot per casing, keep that in your formost thoughts. Best of luck.

Daniel C. Oberloh

[iiipopes]

No less a craftsman than H. N. White himslf, upon making his last set for Bill Bell, vowed never to do it again.

Better to let an expert like one of the gentlemen who contribute regularly to the forum assess the true condition of the casings to see if they can stand being lapped in, then take the rotors, have them trued up, have them plated properly, and refit/relapped in. If the casings are in good shape, the end result will probably be better than new, and you will have much more enjoyment playing a well repaired tuba, even if it costs some bucks to get it that way.

As I have learned the hard way, and with due respect to the engineering skills expressed, knowledge does not equal experience, and something will screw up. Since this is not a situation where you simply go to the parts bin and remake a mis-machined part, namely the casings, general knowledge just does not always translate to the finer points necessary in musical instrument repair, refurbishment and restoration.

[Dan Schultz]

..... A dead school Miraphone 186 or Yamaha 641 would be good candidates....

PLEEEEEZE.... scrap all the 641's you want for parts... but in my opinion, there's no such thing as a dead Mirafone/Miraphone 186 with a good valve section!

Back to the original subject... I would not attempt to make a set of rotors as long as there are old parts to work with. Those rotors are probably tapered not only on the front spidle as Chuck mentioned, ... they are also most likely tapered on the body. I suppose you could go to the trouble to make a set of jigs to hold the rotors while you machine the spindles and cutouts. Your conventional shop equipment such as collet chucks and lathe chucks just aren't capable of making the setups without some customization.

All that being said.... I've been known to spend a LOT more time on something just to see if I can do it and for the learning experience. If you have lots of spare time, and your grandfather has the toolmaking and prototyping experience... go for it. If the project fails you can always buy new rotor assemblies (probably not dual rotors) and stick 'em on the horn.

[Chuck(G)]

If the original poster can do the machining and learn something doing it, I say "have at it". He might make a complete botch of it, but he'll learn a lot.

What's the worst than can happen? He'll mess up the casings something awful and be forced to buy a new valveset. If he's willing to take that risk and invest the time and materials, why not? This after all, is how progress happens.

This brings to mind Mark Veneklasen and his horns (google it). A lot of very innovative thinking and some disastrous blunders. And a lot learned.

Rather than cast this as some space-age precision-machining task, let's consider that there have been rotary valves on instruments for over 150 years. I'll guarantee that a modern industrial machine shop is better-equipped to to precision work than the best shop of 150 years ago. Even Henderson White's rotary valved tubas go back 70 years.

If you can find someone to talk to who actually makes rotary valves for a living, who is willing to chat about it (for some reason, the musical instrument manufacturing business doesn't seem to be interested in sharing), so much the better. Maybe you can have a chat with Gary Greenhoe or the folks at Atkinson.

As an aside, stainless is actually lighter (0.287 lb/cu ft.) than yellow brass (0.308 lb./cu. ft.).

If you try it, please keep the list posted!

[bububassboner]

To answer the question of "shot" the rotors are hollow on the inside and someone has in the past resoldered the back plate on(this is just the rotors not the casings). And now we beleive they are warped so thats why we thought about making new rotors. But I do have an old Yamaha bass trombone that has snapped in have(thank you marching band) that we will pratice with first. Since we have alot of both stainless steel and brass to work with I think we are going to make one out of both and see how they work. But any tips from the people who have done this before would help alot.

[Tubaryan12]

As an aside, stainless is actually lighter (0.287 lb/cu ft.) than yellow brass (0.308 lb./cu. ft.).

Chuck, you might want to check your numbers. Brass is closer to 534 pounds per square foot.
I do work at a horn manufacturer that makes (I think) the best valves in the US. And I would be happy to chat. I'm not going to give away designs or measurements, but I'll share the basics of what I know about making a valve. In fact I will be making valves for a euph in the near future and will be looking for other peoples advice.
-McRobs

I think he means cubic inch as I'm sure you mean cubic foot.
http://www.tesarta.com/www/resources/li ... ights.html

[iiipopes]

Is the spec quoted density or weight? Those are similar, but completely different specifications.

[Tubaryan12]

Tubaryan12. Right, cubic feet ft. not square. But Chuck was really talking about cubic inch.

My bad...I guess I should have been more clear. I should have said Chuck means cubic inches as I'm sure you meant cubic feet.
This one's for me

[Chuck(G)]

As an aside, stainless is actually lighter (0.287 lb/cu ft.) than yellow brass (0.308 lb./cu. ft.).

Chuck, you might want to check your numbers. Brass is closer to 534 pounds per square foot.

That's cu. inch. Sorry, it was early and my brain wasn't revved up to speed.

[Rick Denney]

Is the spec quoted density or weight? Those are similar, but completely different specifications.

I don't follow. Density is just mass per unit volume. Weight is the force exerted by gravity. Therefore, the units of weight are force (pounds) and the units of density are mass per unit volune (pounds-mass per cubic inch). Given that Chuck's values were pounds per cubic inch, that would be density.

You can't know weight until you know the shape of the object. But density is a material property independent of shape.

If you are meaning the difference between pounds-mass and pounds-force, it doesn't matter if the rotors in question are on the surface of the earth.

Rick "fun with units" Denney

[Chuck(G)]

If you are meaning the difference between pounds-mass and pounds-force, it doesn't matter if the rotors in question are on the surface of the earth.

IIRC, the Customary unit of mass is the "slug" not the pound.

[The Big Ben]

I was thinking (that's dangerous):

Would it make sense to use something cheap (i.e. an ebay french horn) to 'shake down' the processes of making a rotor valve before attempting an expensive tuba? A beat-up old Conn 4D can be had for $100 sometimes and the mechanism is similar.

Granddad could "prototype" on the french horn and then, once he figures out how to do it, then do the tuba (or not)

An idea....

[iiipopes]

Is the spec quoted density or weight? Those are similar, but completely different specifications.

I don't follow. Density is just mass per unit volume. Weight is the force exerted by gravity. Therefore, the units of weight are force (pounds) and the units of density are mass per unit volune (pounds-mass per cubic inch).

Of course it is. But since the posted nomenclature was inconsistent, that's why I asked. It's been sorted out at this point.

[Daniel C. Oberloh]

Is the spec quoted density or weight? Those are similar, but completely different specifications.

I don't follow. Density is just mass per unit volume. Weight is the force exerted by gravity. Therefore, the units of weight are force (pounds) and the units of density are mass per unit volune (pounds-mass per cubic inch). Given that Chuck's values were pounds per cubic inch, that would be density.

You can't know weight until you know the shape of the object. But density is a material property independent of shape.

If you are meaning the difference between pounds-mass and pounds-force, it doesn't matter if the rotors in question are on the surface of the earth.

Rick "fun with units" Denney

Double rotors for a tuba with hollow valves; solid stainless or solid brass, they are still going to be quite a bit heavier then rebuilt originals.


Daniel C. Oberloh
Oberloh Woodwind and Brass Works
Seattle, WA
206.241.5767
www.oberloh.com

[bububassboner]

We have brass and stainless steel coming at the end of the week. I'm going to start just by making a copy in both metals of an old Yamaha single trigger bass trombone and seeing 1) if I can make a good copy and 2) checking out the difference between the two metals. I was going to ask later this week but since it's up now, what do you guys think for the F tuba since the rotors are hollow making the rotors for that out of stainless and then drilling out the inside of the rotor to make it hollow then welding a top for the rotor then elecrtopolishing the top of it to make it smooth?Also if you guys think there is a better way to put the top on let me know. My grand-pa's work got a top of the line CNC lathe two weeks ago and he thinks this will be easy on that.(I hope so)[/quote]

[Chuck(G)]

Sounds like the project is coming along.

You probably don't need to patch over holes drilled in the top or bottom of the rotor to lighten it

I'd be kind of interested to see if a ball thrust bearing on the rotor bottom would improve action.

Keep us posted!