TromboneChat

Let's pretend that you had a unique, mega-rare brass instrument and you wanted to get new mandrels made for it so that you could get new and modernized examples of that instrument made. How would you go about doing that?

Would a builder or master tech have the equipment and methods necessary to do it, or would you need to find some sort of specialist (like a bell spinner perhaps) to do it? Could you somehow digitally scan the entire taper of the instrument and reconstruct it into new mandrels via CAD?

I have no idea if I'm even using the right words to ask this, but this is not a strictly hypothetical exercise as you may have guessed. I have a few ultra-rare brass instruments it would be cool to do this with, but I recently acquired an original Kanstul Meehaphone, and that really got the gears turning in my head.

It's going to be kinda pricey. The system can be measured and then the measurements used to create a mandrel. The mandrel will have to be CNC machined to a custom program.

I would guess it may wind up costing somewhere between 2 and 5 times what the instrument sold for originally. You REALLY have to want to do this.

The interior non-curving section of the bell could be cast... in plaster or some other medium... and that could serve as the model for a new mandrel.

Like wise, the interiors of bends and crooks for other parts could be cast.

Could you somehow digitally scan the entire taper of the instrument and reconstruct it into new mandrels via CAD

I'm sure that's possible. Possible...like going to Mars is possible. Someone would have to write the software to take the 3D data of a MRI-ish scan and extract meaningful information for a builder who has to pound and draw and bend all the parts that make up a horn.

But I'm reminded being told of how one of the old-line instrument manufacturers shut down their US factory and sent all their tooling to a new factory in Mexico. New people using the same tools didn't produce the same instruments.

Finetales wrote: ↑Sun Sep 18, 2022 3:59 pm Could you somehow digitally scan the entire taper of the instrument and reconstruct it into new mandrels via CAD?

They did this in Prometheus, with the alien ship. Then they proceeded to get lost in the ship they just mapped. Based on this historically accurate movie, taking place in the future with sentient robots and the like, I don't think it is possible today.

Jokes aside, I think this has been done in the past, at Yamaha. It's possible they had bought the Conn mandrels, but their 88H copies were probably just the result of dismantling an instrument or two, taking careful measurements and possibly a few casts, and then tooling up. Yamaha is a huge company. I don't think this is something a repair shop would take on, especially for a one off copy. Kanstul, if they hadn't been the ones who made it in the first place, would have probably been all about it if they thought they could turn it into a production instrument. Speaking of which, the mandrel probably still exists for the instrument you want to copy....

The price to have a steel bell mandrel made is several thousands of dollars. Then each successive tapered branch needs it's own mandrel (again, at least a 4 digit number per piece) I you want to get into making production parts,such as crooks for tuning slides or branches, ball molds need to be designed and made. Each of those also cost over a thousand dollars.

That is just for the tooling to make some of the parts.

Not trying to poopoo the idea, but just be aware it would be VERY expensive to start from scratch.

Assuming you could get the probe down the bore, a coordinate measuring machine could potentially "map" the inner dimensions of a bell. 3D laser scanning is another possibility.

For those preferring to go "old school", taking a casting with something like CERROSAFE® would probably be the way to go.

Once you get accurate mandrels made for the bell flare and stem, I guess you could find a shop that would do the spinning. The problem is that bell spinning is more art than science, with many variables that are controlled by the feel of the technician doing the spinning. The new spinning technician would have a different feel from the one who made the original bell and you could wind up with a bell that is a dimensionally perfect copy of the original, but doesn't have the same sound or feel.

Ummmmm.
What is a Kanstul Meehaphone ?

hornbuilder wrote: ↑Sun Sep 18, 2022 5:32 pm The price to have a steel bell mandrel made is several thousands of dollars. Then each successive tapered branch needs it's own mandrel (again, at least a 4 digit number per piece) I you want to get into making production parts,such as crooks for tuning slides or branches, ball molds need to be designed and made. Each of those also cost over a thousand dollars.

That is just for the tooling to make some of the parts.

Not trying to poopoo the idea, but just be aware it would be VERY expensive to start from scratch.

Oh don't worry, this isn't an idea I had that I thought I could realistically make happen quickly or cheaply. This is just out of curiosity more than anything - if you really wanted to preserve a unique instrument by making new mandrels for it, it could theoretically be possible to get grant funding to foot the bill. Or you could just be rich!

Based on all the replies it's good to know that it is theoretically possible if you have a truckload of cash.

JohnL wrote: ↑Sun Sep 18, 2022 6:01 pm Assuming you could get the probe down the bore, a coordinate measuring machine could potentially "map" the inner dimensions of a bell. 3D laser scanning is another possibility.

For those preferring to go "old school", taking a casting with something like CERROSAFE® would probably be the way to go.

Now we're talking! Testing the viability modern tech to get digital renderings that could then be made into steel mandrels seems like a way to get people interested.

CharlieB wrote: ↑Sun Sep 18, 2022 7:17 pm Ummmmm.
What is a Kanstul Meehaphone ?

It's an enormously rare drum corps G bugle that is essentially a big flugelhorn in G with a massive bell throat - even my bass trombone mutes don't fit! It can sound as dark and smokey as my Couesnon flugel, or rip your face off with sound. But, it only has two valves and very few were ever made. Mine is the first I've ever seen still existing today.

CharlieB wrote: ↑Sun Sep 18, 2022 7:17 pm Once you get accurate mandrels made for the bell flare and stem, I guess you could find a shop that would do the spinning. The problem is that bell spinning is more art than science, with many variables that are controlled by the feel of the technician doing the spinning. The new spinning technician would have a different feel from the one who made the original bell and you could wind up with a bell that is a dimensionally perfect copy of the original, but doesn't have the same sound or feel.

Ah, there's our old nemesis, Process, back to spoil the fun. You could have the original analyzed and sort through heats of brass sheet until you found some that was pretty close (good luck finding a supplier who will let you do that, but at least it's within the realm of possibility). As we've been discussing, duplicating the dimensions is probably doable. But without detailed information on the exact steps used to turn raw material into a finished bell, your chances of producing something that replicates the sound and feel of the original are only slight greater than zero.

Lots of good point above.

A couple more, in no particular order:

1) I'll be posting in a while about using a telephoto digicam and a tool called "engauge digitizer" to estimate the nearest Bessel function parameters for bell shapes. Been whittling down the post for a while. I use the method on the OUTSIDE of the bell, but it should do fine on a casting of the INSIDE, OR one can do math to estimate removing bell thickness. Of course, the bell thickness almost certainly is NOT uniform. But the method can still retrieve things repeatably.

2) H.N White had some disks and a rod hanging amongst the tools at the King factory. George McCracken figured out they were for measuring bell tapers.

3) When writing your grant for the bell mandrel, don't forget to price out the mandrels and drawing dies for the tuning bow and neck pipe, which are also part of the bell taper. On the Duo Gravis they drew the tuning slides to have straight outer and tapered inner profiles as well, so there are some more mandrels to figure in.

4) There have been, and continue to be, interesting studies of historic instruments. I seem to recall one within the last decade that uses acousitc reflectometry to characterize bore shape.

Even after all that, I tend to agree with John's point: there was and still is so much variability in the process that regardless of how much you spend on the project, the sonic result is likely to be a bit of a surprise

The Institute for Musical Acoustics in Austria had a software/hardware package called BIAS (brass instrument analysis system) which seems to have disappeared from its web site -- maybe they spun it off to a private company? It had a transducer that plugged in where the mouthpiece went and swept a range of frequencies through the instrument and measured the impedance at every frequency and then gave you a read-out of the slots and intonation tendencies and also displayed a very accurate bore profile for the entire instrument. You used to be able to download the software for a free trial. Without the transducer you couldn't measure any existing instruments, but you could input your own data and see what it did. It was super fun.

boneagain wrote: ↑Mon Sep 19, 2022 4:46 amEven after all that, I tend to agree with John's point: there was and still is so much variability in the process that regardless of how much you spend on the project, the sonic result is likely to be a bit of a surprise

I like surprises!

I don't think the goal is really to make an identical copy in terms of sound and feel. If a taper is unique enough, it'll still sound like that instrument even if it has a different flavor. A trombone still sounds like a trombone no matter who made it, or how they made it. I think very unique tapers should be measured and preserved so that the original designer's work can continue to bear fruit.

I look forward to your telephoto digicam post!

My wife had a 3D laser scan of her mouth in prep for some dental work. It was interesting to watch the computer build the model while the tech scanned.

Once you have the model, might be able to find a school with cad/cam. In engineering school in the 90s we programmed to cut shapes out of blue wax that was melted and reused. The high school my kids went to in the mid 2000s had a machine too.

That won't get you steel but you could do a wet layup, or even a lost wax casting.

I'm just going to say that people have been making copies of bells for much longer than 3D scanning has been available.
Also a number of instrument makers make their own mandrels for much less cost than buying one.
For a single copy or a small run, a wooden mandrels might also a cheaper alternative (but much less durable) than steel.

From a practical standpoint of someone who does reverse engineering regularly, 3D scan might get you a portion of the data, but it will mainly give a check on outer dimensions. The most accurate inner dimensions are going to come from gauge balls. You're also going to want hardness numbers from the various materials to determine the heat treat condition. And you'll probably have to disassemble the horn to determine some things like type of solder used or inner dimensions of the cork barrels, etc. For the bell thickness profile, you might even need to cut the bell along the axis (destructive). Without that, you're counting on your ability to register the inner profile to the outer profile when the overall thickness is probably around 0.020" - which is likely about the same as your registration error.

But as Brennan said, (paraphrasing) you don't have to get that last 3%, the first 97% is where the important differences lie.

LeTromboniste wrote: ↑Tue Sep 20, 2022 6:39 am
Also a number of instrument makers make their own mandrels for much less cost than buying one.

Bell mandrels are not something you can just go out and buy. They are purpose made-to-order items. Even making a mandrels yourself (which I have done) takes a LOT of time, plus the cost of material. They are not cheap!

hyperbolica wrote: ↑Tue Sep 20, 2022 8:35 amFor the bell thickness profile, you might even need to cut the bell along the axis (destructive).

You should be able to get the thickness profile using an ultrasonic scan.

hornbuilder wrote: ↑Tue Sep 20, 2022 8:54 am

LeTromboniste wrote: ↑Tue Sep 20, 2022 6:39 am
Also a number of instrument makers make their own mandrels for much less cost than buying one.

Bell mandrels are not something you can just go out and buy. They are purpose made-to-order items. Even making a mandrels yourself (which I have done) takes a LOT of time, plus the cost of material. They are not cheap!

Yes of course, I'm aware. Making them is still several hundred bucks plus days of work. But my point was it is anyhow cheaper than buying one ready-made, and there might potentially be ways to make it even cheaper if it's just to make very few copies, where the mandrel doesn't need to survive long.

I don't have a lathe, but would it really be that hard to turn a bell mandrel out of the appropriate wood?

Especially a short one like that bugle?

timothy42b wrote: ↑Wed Sep 21, 2022 6:23 am I don't have a lathe, but would it really be that hard to turn a bell mandrel out of the appropriate wood?

Especially a short one like that bugle?

To make “a” mandrel that is roughly bugle shaped? Probably not. To make one to be an exact copy of a particular taper with the design resolution fine enough to differentiate it from other tapers? I doubt the measurement techniques and choice of wood as a material to consider this a feasible process.

Sure, you can make something… but what is the question we are trying to answer?

Cheers,
Andy

Rifle chambers are duplicated by filling with cerrosafe. Is there something you can let harden inside and extract to measure?

I believe Cerrosafe can be used with brass as well. If not, a polymer could be used. Maybe even foam-in-place material (not terribly good to use as a mandrel later, though).

timothy42b wrote: ↑Wed Sep 21, 2022 6:23 am I don't have a lathe, but would it really be that hard to turn a bell mandrel out of the appropriate wood?

Especially a short one like that bugle?

Further research on the meehaphone has revealed to me that the meehaphone's flare is not as unique as originally thought (as is often the case with G bugles). It is apparently the exact same flare as the Olds BU-10 and Conn 92L French horn bugles. So, it would seem no duplication is necessary to make more meehaphones.

Still, the meehaphone is far from the only instrument this process could be useful for.

"2) H.N White had some disks and a rod hanging amongst the tools at the King factory.
George McCracken figured out they were for measuring bell tapers."

As the story goes, Zig Kanstul used precisely this technic to measure the leadpipes of borrowed trumpets when he was commissioned to re-release the F. Besson trumpets by Boosey & Hawkes in the early 1980's. The original tooling from Fontaine Besson was still available, but so worn as to be mostly useless. Kanstul was able to borrow and measure 40-50 pre-war French Bessons of Meha and Brevete design for non-destructive measurement and testing. They varied so much Kanstul released 3 bore sizes in each model for B-flat. The C trumpets varied so much, 2 bore sizes of Meha were released only, each with 3 different cuts of the leadpipe mandrel and a swappable leadpipe arrangement. Numbered 65,67,68 and 7x for the larger bore, the first digit described .460 or .470 bore for the instrument, and the second digit described how many eighths of an inch from the top of the mandrel the pipe was cut. A larger second digit was cut further down the taper, giving a larger opening and resulting more open pipe with a faster taper. Zig made his leadpipe mandrels based on averages of the wildly divergent measurements revealed by the rod-and-disk technic. The instruments were hand fitted at the factory. If a part wasn't suitable, another was tried from a large inventory until one fit properly without slop or stress.