TromboneChat

I have a Cool Wind trombone that is playing awfully airy. I knew there was a leak somewhere.

This one has no "stockings" (copper sheathing on the end of the slide). I did something with paper tape that made things better, so I know that I'm on the right track.

Can some people with plastic trombones (any of them -- Tromba, pBone, Tiger, etc. as well as Cool Wind) measure the outside diameter of the inner slide tube in the middle and the outside diameter of the stocking area so I can figure out how thick I should make my improvised stocking?

Bruce,
I'm at work, but I'll measure both pBones when I get home.

I have a plastic tenor and an alto. I moved to the alto this summer when I was having left wrist issues and that's what I've been doing my morning warmups on. I do occasionally play the brass tenor in the evening. In COVID times with no playing opportunities it's hard to keep the motivation to practice up beyond some basics to maintain.

Like you I think stockings make a big difference. Years ago I made some crude trombones out of available CPVC pipe from the big box stores. The fit between inner and outer slides was very loose. I ended up putting some copper couplings in the opening to the outer slide, and that changed the way these played. The slide action worsened of course, remember that straight is not a word that applies to PVC. But the squirrely partials suddenly lined up. I hadn't realized a leak made that much difference.

Airy sound? I'm not sure I'd expect that as a symptom though. I'd expect difficulty centering and maybe some squirrelly partials, and maybe a really bad individual note. Remember the feedback from the bell is very different from plastic, even though the sound out front may be the same.

I suspect a decent seal could be wound on to the ends using suitably sized thread. Polyester likely best. It would not have to be pretty with the loops lining up like a sword handle, just achieving the right diameter, which may have to be discovered by repetition. A pretty good seal at the top of the stocking and at the bottom is likely good enough. Could superglue the ends.

baileyman wrote: ↑Fri Oct 30, 2020 7:26 am I suspect a decent seal could be wound on to the ends using suitably sized thread. Polyester likely best. It would not have to be pretty with the loops lining up like a sword handle, just achieving the right diameter, which may have to be discovered by repetition. A pretty good seal at the top of the stocking and at the bottom is likely good enough. Could superglue the ends.

Actually, tape looks like a good fix. I am debating whether to use copper or polyimide (Kapton). I can get the copper in 0.001" thickness and 0.0025" thickness, while the polyimide seems to go at 0.002" thickness. I figure on using the piston ring approach of several bands with the seams offset.

For that matter, for a thicker stocking I can check out plastic package sealing tape. I have a bunch of that stuff hanging around here.

I did use your thread approach to fix one joint on a tenor recorder. Worked great, but in that case I was filling a channel.

I tried measuring with a caliper and a Scherr-Tumico micrometer.

These measurements depend on the roundness of the tubes and... they're not. So the error band is significant here. But very roughly, the OD of the inner slide on my mini pBone is .546 and the stockings are .561.

I think if your slide is straight enough, it might be better to do the seal on the inside of the upper end of the outer slide, because then the amount of clearance remains constant no matter where the slide is. If that end were thick enough, you could even do a piston ring approach like mentioned. The stocking serves two purposes, right? To be a bearing surface, and to improve the seal? It seems to me if you separated those functions you might be able to optimize either better.

Thanks, Tim.

Clearly I'm looking for a running clearance, not a really tight fit.

But an 8 mil thick (approximately) stocking it really big. Take several layers of tape. I may see if less works OK.

Shouldn't this be titled trombone players who play plastic trombones? LOL!

Playing a plastic trombone is really an oxymoron.

Slightly off topic, but having to do with measurements. I have an inexpensive plastic vernier calipers, nothing precise enough for a machinist, but accurate enough for everyday use and I reach for it a lot. It was probably about $10 but has been incredibly useful. But I had real doubt in my measurements today, because

a little later I needed a 30 inch piece of 1/4 inch PEX. I bought a 5 foot length for under $2, and measured 30 inches from one end. I cut it, and then noticed one piece was almost 2 inches longer than the other. Well carp! obviously I'm not focusing today if I can't cut a piece to size, maybe I screwed up Bruce's measurements too. Now, I measured from one end, not both, doing that is considered a sin. So now I measured carefully with a metal rule instead of a tape, and sure enough, it turns out that from a 60 inch piece of tubing it is possible to cut one 30 inch and one 31 3/8 inch piece.

I just want to know how you could measure 30 inches (that's nearly a meter!) with a cheap plastic caliper

I think that lengths from the lumber yard are cut "long" figuring you won't be upset having to trim off a little extra but you'd be really upset if the piece was too short.

Talking about cheap plastic things, I once got a cheap plastic (SP brand) slide rule and multiplied 2 by 2 and got 4.2. Now that's "precision"

BGuttman wrote: ↑Sat Oct 31, 2020 7:25 pmI think that lengths from the lumber yard are cut "long" figuring you won't be upset having to trim off a little extra but you'd be really upset if the piece was too short.

That's a common philosophy in many situations when selling a commodity by weight or length. Rather than risk shorting the customer, they will give you just a little more. That 16 ounce (~454 g) box of corn flakes probably actually holds at least 16.1 ounces; there's always a small amount of variation in the machinery that fills the boxes so they if they set it at precisely 16 ounces, roughly 50% of the boxes would actually be "light" by a tiny amount.

BGuttman wrote: ↑Sat Oct 31, 2020 7:25 pm Talking about cheap plastic things, I once got a cheap plastic (SP brand) slide rule and multiplied 2 by 2 and got 4.2. Now that's "precision"

Oops. Giving away your age here, Bruce.
Slide rule....I still have two in the attic. A Pickett and a K & E.
They weren't fully retired until electronic calculators advanced to doing roots and trig functions.
Around 1973 ??

Yup. I have one of the earliest calculators, a Hewlett-Packard 35 (and also a 67). I got into Reverse Polish Notation at the start. Still prefer it for calculators although most of them now don't use it.

I don't know what I did with that SP slide rule, but I have 3 K+E and one bamboo unbranded one. Back when I was in college taking an Engineering degree (late Pre-Cambrian Era) that was all you had. In the Computer Lab there was a Wang calculator (the one with Nixie Tubes) and the computer was an IBM 1620 with the remarkable capacity of 20K words. The stuff we could do then is laughable by today's standards.

BGuttman wrote: ↑Sun Nov 01, 2020 12:39 pm The stuff we could do then is laughable by today's standards.

Ramblings of an old engineer.....
Time has relegated the old slide rule to museum status, and compared to today's computers, the slide rule is a pretty primitive tool; but it got us through two world wars, and took us to the Moon. Not too shabby for something with no batteries. Not real accurate for precise calculations, though. I still have memories (nightmares?) of extrapolating square roots longhand, cube roots and up required the big logarithm book that also included the trig functions and their logarithms. Remember logarithms? My first "real" calculator was a Hewlett Packard 27. LED display. Batttery lasted maybe six hours if you used it sparingly. Thought I'd died and gone to heaven. Reverse Polish notation and all. I still have an HP32S hand-held calculator on my desk. Use it every day.
Hmmmmm. This is a trombone forum. Gotta get on topic. If you need to measure that plastic slide, I can loan you my machinist's caliper. No digital readout, though. You'll need to read the vernier. That's sorta like a slide rule.

I have a nice vernier caliper buried somewhere in the basement. Haven't needed it since I retired. Even has a digital readout, although the battery doesn't last if I don't use it.

I also have a micrometer somewhere. Non-digital.

I checked my CoolWind trombone today. There isn't 7.5 mils clearance on each side from the inner to the outer. Must be different from the pBone. I think I'm going back to my 2 mil tape idea.

BGuttman wrote: ↑Sat Oct 31, 2020 1:59 pm Playing a plastic trombone is really an oxymoron.

Well, I made a set of "stockings" using plastic carton sealing tape. Made things better. I think I need to find tape that is just a hair thicker. Maybe polyimide?

I found that my Mt. Vernon 1 1/2G had much better sound than a Wick 4.5 AL or a Marcinkiewicz 105. I thought this thing was supposed to be a tenor. Should I think about replacing the leadpipe? (And which ones have a fine thread?)