measuring a tapered pipe

Maybe you could ask a dentist about the stuff they use to create moulds for crowns/dentures.

Hi, not knowing how much of a curve you are talking about this may not work, but if not too sharp, simple gelatine can be cast and literally blown out of the tube. We use agar in the lab and fairly high % stuff can be pretty stiff but still flexible. Gelatine is likely about the same. With some care, even if it breaks a little, you might be able to get some measurement. Again, not knowing how sharp a turn and how precise you need to be, this may not work.

Reprorubber. The first hit on the web is this:

We use the blue stuff a lot at work. We usually make a bit extra and if you keep rolling it between your hands while it cures you get a perfect ball that bounces like a superball.

This is interesting. What for?

I've used this stuff called "Alumalite". It's a silicone rubber that's made for making molds. It's available at hobby stores. Also, here's a url for someone selling molding supplies who will give you a free sample.

. Alumilite is expensive. I don't have any experience with the fellow at the above url or with his prices. Silicone rubber is nice because it doesn't stick to the item being copied. There is also a metrology rubber called "Repro Rubber". It's good stuff but really expensive. ERS

I need to measure some of the tapers on an old french horn so that it can be reproduced. LB

Local museum has plastic molds the kids use to make plaster mummies and dinosaurs. Docent didn't know where the stuff came from, so all I can suggest is that if a museum's Ed. department has it, the stuff can't be real expensive. Tho' not as spiffy as the stuff ERS mentioned.

LB

If that horn is old enough, you may be talking hand hammered, rolled, and soldered tubes, so wall thickness is variable depending on which way you measure. You should post to the Musical Instrument Makers Forum,

. There are a bunch of clever people there, some of whom make brass winds.

You might also look at Robert Barclay's book, "The Art of the Trumpet-Maker" which is about making replica 17th and 18th century Nuremberg style trumpets, but covers a lot of the same processes as were used making horns.

My guess is once you get out of the bell region down into the tubing part, the wall thickness will be pretty uniform. I'd do a bunch of measurements with a long arm caliper at every point you can reach, at several points around the circumference of each tube you can reach into, and see if there is a statistically significant variation. You may not need to make a cast replica (which is always dicey because minor registration errors will cause huge wall thickness errors).

In point of fact, wall thickness, except in the bell, is insignificant to the sound of the horn. Even the shape of the air column is immaterial, which is why you can fold them up and have elliptical sections near the valves and at the sharp curves. Only the volume counts.

Interesting problem.

Good luck

Jim

I would try silicone rubber potting from your local building supply with some hollow glass microspheres added for filler. How much microspheres to add would take a little experimentation. Too much and the result is not flexable enough to get it out in one piece. Too little and it would be too flexable to get good measurements.

Dan