Stealth Tuba Trial

[karltuba]

I was just visiting Santa Cruz with my girls, and having seen the write-up on the stealth tuba I thought I would give Brian a call and check it out. Well, it was a very fun and interesting time. The tuba is not comparable with a BAT - I would not play on it in my orchestra (even though my hall is not big enough for a BAT) - BUT it is a wonderful little horn that plays surprisingly well. The most important thing about it, though is the "indestructibleness" of it. I think it is very commendable of Brian to be giving so much thought into the idea of putting well made instruments into kids hands for a very reasonable price. We could all use a bit of this idealism and think about how we can best get people interested in what we are doing on the tuba. Brian's idea of getting "cheap" horns into kids hands is a great way.

Here are a few pictures of the horn in action (my daughter Maja is playing in the one picture...)

Have fun, and if you are ever in Santa Cruz do look Brian up. Thanks to Brian for the nice visit!!!

Karl Schimke
Tubist, Sinfonieorchester St. Gallen, Switzerland

Stealth-Tuba-1.jpg

Stealth-Tuba-2.jpg

Stealth-Tuba-3.jpg

[TubaCoopa]

What exactly is the clear part made out of? I'm assuming it's some durable plastic.

[Thomas Maurice Booth]

http://www.youtube.com/watch?v=x4-QQCKN1Co" target="_blank

Here is a video of a trombone made entirely of glass, mouthpiece and all. Sounds decent but I wish there'd be more playing without the plunger.

TMB

[Tubaing]

Will the plastic dent or crack?

[Rick Denney]

Will the plastic dent or crack?

Sure, if you hit it hard enough. But PETG (Polyethylene Terephthalate copolyester modified with glycol) is very strong--at least as good as polycarbonate. At 75 pounds/cubic foot, it's less than 1/6 the density of brass. The yield strength is about a third of annealed brass, which means you can make it five times as thick as brass and be stronger and still lighter. The yield strength is nearly as high as the ultimate tensile strength, meaning that when made thick enough to be very strong, it will probably not dent. A big enough hit to dent it would just as likely crack it, though it has good elongation so it will not shatter. Brass, on the other hand, has an ultimate strength anywhere from 50% to 300% higher than it's yield strength, depending on how it's worked.

The big difference is that it is not nearly as stiff as brass. The modulus of elasticity for brass is about 100 times more than for PETG. That means that if you took a bar of brass and a bar of PETG the same size, and loaded them the same way, the PETG would deflect (change shape as a result of the load) 100 times more. Some of this difference is compensated by the PETG being much thicker. If this tuba plays reasonably, then it seems to me that it utterly dispels the myth that one brass alloy can create different acoustical effects compared to another. If red brass were different than yellow brass, for example, this instrument, being thousands of times more different in terms of inherent material stiffness, shouldn't even play like a tuba. Since it, uh, clearly does play like a tuba, the notion that subtle differences in material properties are important seems to me highly unlikely.

I would expect it to resist damage by about the same margin as a Kelly mouthpiece resists damage compared to a brass mouthpiece.

PETG looks like interesting stuff. It can be sterilized and it's approved for food processing applications. It's a thermoplastic and can be easily extruded, molded from flat sheets (probably how Brian shaped it), or blow molded. Scratches can be melted out of it with a heat gun. It can be heat welded, solvent welded, glued, and mechanically fastened (using the correct screws). It's easy to machine and much more machinable than polycarbonate. The temperature resistance is reasonable for plastic, but it will melt at around 175 degrees, so don't boil it. Static dissipation is good for plastic. It can be painted, but I would not expect paint to adhere really well, so my temptation would be to create a haze surface on the inside using a mild abrasive and then paint it with an epoxy paint. Then, the plastic itself will provide the gloss on the outside and the color will shine through it. You may be able to get it with a color molded into it, but I suspect it will always be transparent.

Chemical resistivity is even pretty good. Keep toluene and acetone away from it, and don't clean it with ammonia glass cleaner, but beyond that nothing to worry about.

I would not use it for valve branches, however. The thermal expansion of plastics is just too much to work well for tuning slides.

I'm no real expert on the variety of plastics, but of those I've looked at, this one seems as good a choice as any and better than most.

Rick "wondering how Brian joined the seams" Denney

[NC_amateur_euph]

Rick (Resident Genius) wondered how Brian joined the seams.

I wonder how he formed and shaped the conical sections, especially the bell. The only methods I can think of (without serious navel-gazing) seem wildly impractical.

[Rick Denney]

Rick (Resident Genius) wondered how Brian joined the seams.

I wonder how he formed and shaped the conical sections, especially the bell. The only methods I can think of (without serious navel-gazing) seem wildly impractical.

I don't know how he did it. But I know how I would do it. I would start with an instrument of good design and take it apart. I would then make a plaster mold of the branches, with a few pieces of tubing. Then, I would buy sheet plastic of the proper thickness, cut it to the approximate shape, and then lay it over the mold. I would then apply heat until the plastic melted and sagged into the mold, applying vacuum to the tubes to draw it tight to the mold. The pieces could then be trimmed and fastened together using solvent welding, and a heat gun could be used to melt off imperfections from molding.

It sounds easier than it is, of course, but it's gotta be a LOT easier than working brass into the right shape.

Rick "thinking Brian's joints look more like heat welding than solvent welding" Denney

[tofu]

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[TubaCoopa]

PS tubacoopa – this tuba is PETG (coke bottle material) but there are lots of plastics that would work.

They also make t-shirts out of PETG. Hmmm. I wonder if you could make a tuba/t-shirt combo...