Tuba with bulged casings?

[Doug Elliott]

The outside of the casing is not necessarily representative of the inside. The inside needs to be measured at several different points and angles along its length to see if it's straight, tapered, or out-of-round, and how it compares to the outside of the piston to see how much clearance is there. The outside of the casing is totally unrelated.

And anyway a pencil is not a reliable straightedge.

[Ken Herrick]

Some accountants use LOTS of crooked pencils and pens: There IS a market.

Take Doug's word as accurate.

[Rick Denney]

I didn't read that earlier conversation, but usually what makes a casing become misaligned is trauma, transferred through braces and tubing.

In terms of their construction, when the casings are brazed to the knuckles, there may be some deformation from heat. But it's no problem because the casings are bored to accept the valves after that, making their insides straight even if the outsides aren't. That's why Doug says you have to measure on the inside to know what's up. But it's not easy--measuring bores is notoriously difficult.

If it's spilling air because of a gap between the casing and the valve, then probably something deformed the casing after it was originally bored. Not all trauma happens after the horn is sold--it could be an artifact of assembly if the problem has always been there.

Rick "good diagnosis looks for primary, not secondary, effect" Denney

[The Big Ben]

Pencils are not reliably straight. A pencil works fine as a pencil even if it has a bunch of wowies in it. If the lead can be sharpened, it's a pencil. Besides, the measurement of the outside of the valve casing is of little consequence in the performance of the valve. You need to measure the inside of the bore.

You could use a small steel ruler (about 1/2" wide and 6"-8' long and 1/16" thick) to see if the casing bores are straight but wouldn't be able to measure the actual diameter of the valves at different levels. There are inside calipers which are specifically made to measure bores. If you don't have a instrument tech close by who has a caliper to measure this inside bore, a gunsmith should have a gauge that could measure the valve bore and might be willing to measure your casings. There may be calipers which would be "good enough" at the hardware store. The important thing is to get them measured. If the top, middle and bottom are not the same size (or within tolerances), you know you have a problem. The size of the piston has to be pretty close to the size of the bore the entire length of the bore if it is going to be sealed with valve oil. It might be less likely that the pistons (even though they look shiny and supposedly have been plated) are of varying size top, bottom and middle but it wouldn't hurt to measure them.

My personal experience with a valve job was that the casings were made straight and true then the pistons were compared with these straight casings and then sent to be plated larger and, when they got back, they were honed to get a fine fit. This series of photographs show the process used to rebuild and restore the valves on Bandmaster's Holton 345 BBb. The valves were in very poor shape and needed more work than your valves might need but it gives you a clear idea of what might be involved in the process:

http://www.oberloh.com/gallery/tubavalvereferbish.htm" target="_blank"

Hope this helps.

[Donn]

Pencils are not reliably straight.

I think the first time, the point was well taken, but if as it seems we're getting ready to make this into one of today's great causes, I think it might be a good opportunity to think about the context within which we make measurements and observations.

If I thought Oberloh, following the valve rebuild example, might have used a wood pencil as a straight edge reference while setting up his honing machinery, then indeed it would be cause for concern. On the other hand, there are other tasks that don't require that level of precision - say, adding a water key somewhere on a tuba: if you had to delay that work because the machinery wasn't available to get a hole drilled at the right angle and width to 0.001 inch accuracy, I'd suspect that you don't know what you're doing. In my opinion, a picture of the outside of a valve casing, for the sake of discussion on an internet bulletin board, is not something that calls for obsessive attention to repeatable accuracy. It's good to note, as Doug did right away, that a pencil isn't reliably straight, but from there it would be more conducive to an useful discussion to proceed on the assumption that this pencil was as straight as most pencils are.

[Doug Elliott]

I think this thread kicked off lots of great info from way more qualified people helping someone with a pencil and an airy tuba.

Follow up- how are worn casings built up again?

The casings aren't built up. They're honed until they're straight, round, and consistent all the way through. The pistons are built up with plating until they're "too big" and honed back down to the right fit.

At least that's how I understand it. I've never done it myself, that's not the business I'm in, but I do understand the necessity for precision.

[EdFirth]

I've encountered this phenominon a few times, where only one valve was leaking like crazy. Twice it was on ex military horns where the valve was removed when they wrote them off the books. In both cases the valve was a little too small And the valve guide needed to be in a slightly different place. Or, maybe in this case someone did an "economy overhaul" and plated all of the valves but the replacement one is still too small. And, possibly, the guide isn't exactly where it needs to be. If you can remove the guide you can turn the valve to different spots and see if the slide pull pop comes back. The other time I encountered this was on my baritone which had been de dented and had the leadpipe replaced. I guess he overheated the first valve casing in the process and it warped.The horn was a terrific player before the repair and royally stunk after. I also found hammer marks on the casing from him trying to get it enough in round for the valve to function, which it did. One more thought, 1 and 3 are usually interchangeable so you might try switching them to see if it makes any difference. Hope you get it figured out. Ed

[Dan Schultz]

Interesting thread. I've never seen a 'bulged' piston casing.

I have seen one case where someone tried to remove a 'ding' in the casing by pushing the casing wall outward. Anderson discovered the problem when I sent the valve section in for rebuilding. Even after they honed the casing as far as they thought they should... there was still a spot inside where the casing didn't clean up. They called and asked permission to 'peen' the outside of the casing to give them a little more material inside to work with.

One of the big problems with cleaning up badly worn or ovaled casings is that the depth of the guide slot can get very shallow.

It doesn't take much clearance around a 1" or so diameter piston to equal a very bad drop in compression. A couple of thousanths of an inch is like trying to play with a waterkey open.

[PaulMaybery]

I often imagine the effects of leaving a horn is a sub-zero car overnight. With condensation around the valves, the power of ice at 20 below has "just a little bit" of force. Ice is used to split granite stones. Perhaps that particular horn lived in Minnesota. On a side track here: That sub zero temp also has a long term effect if continually repeated in a freeze-thaw pattern. Different metals such as the brass tubing and the lead based solder expand and contract at different rates, and I can see that the solder joints may eventually become compromised and weakened. Not a big deal in much of the country, but here in the upper midwest a different story.

[Michael Bush]

I just followed the link to your web site in your signature. I owned your 1912 Conn at one time. You mention Bob Pucci as a previous owner; I bought it from him. I remember taking a detour almost to Vermont on a work trip and meeting him in the parking lot of a classic New York diner.

All of this is prelude to saying that all along as this thread has been growing I've thought about that tuba. I ended up believing it had some of the problem this thread is about. I had to use really heavy valve oil, and ended up concluding that at least one of the valves, maybe more, I don't remember now, had not just a worn piston, but a bulged casing. I gather the young man I sold it to had the valves worked on, and perhaps that fixed it?

[Matt Walters]

Wow.

[Doug Elliott]

Ice is an interesting theory, but pistons are much thinner material and presumably more flexible than a casing ever would be. Freezing water expands into any available air space, so it seems to me the only way for to the casing to be expanded is if it were completely filled with water and frozen solid, which is very unlikely. I think it would damage the piston long before the casing. And with lots of brass instruments living in cold climates, it would be a common problem, and it's not.

Clearance between a piston and casing is only a couple of thousands of an inch, maybe as much as four or five. Much more than that and it leaks.

[Michael Bush]

I believe he told me the valves were overhauled and the 1st valve slide modified to be moveable. The old girl plays.

That might speak in favor of the "just worn" theory. Anyway, everyone seems to agree it would be possible to check with the right tools, whatever one ends up thinking that means.

[The Big Ben]

Wow.

+1

[Dan Schultz]

.... As an aside, I performed the pencil test on most of my other horns and they all passed. The one that didn't pass plays super airy.

What brand/kind/hardness of pencil is that? I need to add one to my workbench!

Of course.... I'm just joking with you. I'm a retired mechanical engineer and can tell you that I've seen a lot of stuff that's tough to explain in the 'machinery World'. If I dug deep enough I could determine exactly how much pressure ice exerts when contained in a vessel and what thickness of brass it would take to contain the force.

Chalk it up to '**** happens' and move on. Take that valve section off the horn and send it to Anderson. They will fix it and couldn't care less how it happened.

By-the-way.... the air pressure involved in pushing and pulling a slide is not going to come anywhere near what it takes to overcome the modulus of elasticity of a brass valve casing. Besides.... there are many areas of a tuba that are thinner to take the 'hit' if that was possible.

Paul.... I can't even begin to wrap my brain around the theory of moisture inside the valves freezing and causing a problem. (Just to make sure I am not full of crap... I have a bunch of pieces of telescopic tubing. I'll put a couple of pieces through some freeze and thaw cycles. You don't even need to put your samples in the freezer this time of year. Just set 'em outside!)

You guys need to move on to a more viable topic... like perpetual motion!

[The Big Ben]

The only problem I have ever heard of from water and ice in tuba/sousie valves were guys complaining that when they played their horns outside in cold weather (Minnesota cold), played for awhile and then sat the horn down for 10-15 minutes, when they picked it back up again, the water in the valves from playing froze and seized the valve. Blowing through the horn freed them up. Obviously, they weren't stuck too tight.

[Daniel C. Oberloh]

Amusing discussion, Yeah, I have seen bulged casings but they were always caused by some fool doing something to the casing cylinder that they should not have been doing to begin with. Like pistons, casings can be bent, warped, dented… The outside state of the casing can be an indicator of where the problem exists but not necessarily. Cylinder conditions are best detected with careful use of a dial bore gage. If the cylinder is deformed, it can often times be corrected thru a honing process that quickly and simply straightens the cylinder with minimal loss of material (.0005'' or less) from the cylinder wall. For the record, I find a machinists ruler or straight edge a better indicator of straightness then a pencil and a pencil a better writhing instrument then a straight edge.


Daniel C. Oberloh
Oberloh Woodwind and Brass Works
http://www.oberloh.com

[The Big Ben]

Writhing? As in "writhing in pain"? Isn't that what happens when you hit your thumb with the hammer?

[Donn]

Yes, something of that nature is certainly called for. I'd like to put hose clamps around my valves just in case, but unfortunately, in the middle where I gather they'd be most likely to bulge out, there's no clear place where the hose clamp band could pass around the casing! Alas.

[Dan Schultz]

Paul.... on your theory that condensation between the piston and the inside of the casing in freezing and thawing environments might possibly cause the casings to bulge....

I just couldn't stand thinking about all the 'whys and wherefores' so I cut two pieces of inner and outer King slide tubing about 6" long and have been subjecting them to cycles through my home freezer.

I cleaned the pieces of tubing so they were free of lubricants, bathed them in plain water, slipped them together, and put them into the zero degree freezer. Then took them out of the freezer and thawed them with warm water... slipped them back together without drying them... and put them back in the freezer.

They've been through about twenty-five cycles with no significant change in size. My measuring tools are only good for perhaps +-.0005" so I cannot honestly say that there has been NO change. But... there certainly has not been what I would consider 'bulging'.

Considering that these tubing pieces have wall thickness substantially less that a casing or piston... I'm thinking this experiment was conclusive.