Brass sheet bell blank dimensions?

[TromboneSam]

I’m getting a really dumb, expensive idea BUT have some questions and figured I’d ask the hive mind before getting too committed by directly calling a horn builder.

For one piece bells, does anyone know the size of the sheet required to make the blank?

Maybe a better question, does anyone know the dimensions of the blank as they relate to the bell size? I’m trying to figure out the minimum dimensions required of a sheet of brass to make a bell.

Googled and didn’t find much, but maybe I’m typing the wrong thing/looking in the wrong places?

[LeTromboniste]

Bell patterns vary widely depending on the desired shape/size, but also on the desired thickness profile. Basically the tail of the pattern is roughly as wide at any point as the desired circumference of the finished bell stem at that same point, plus the depth of the teeth for the brazed joint. But the shape of the flare portion and how much "wings" it has can vary a ton. The more wings/the more overall surface, the closer to an actual bell it will look once the back is "broken", and the least amount of stretching it will need, therefore the flare will stay ticker. A pattern with less wings will be more cone-shaped once opened up, and will need more hammering and more passes of inside spinning to get the flare formed. For the same bell size, less material means more stretching, which means a bell that gets much thinner towards the rim.

Tl;dr there is no direct correlation between the size of the finished bell and the size of the pattern.

[elmsandr]

I think the answer here is somewhere along the lines of “if you have to ask, you don’t need to know.”

That is, you should have a design and a process plan for each step of the blanking, rough forming, folding, brazing, rounding, and spinning steps that define what the stock shape is before and after the process. If you don’t have a design and are just winging it, buy what you can get and have fun. Buy extra so that when you learn what doesn’t work you can adapt. Look up images of different bell makers, you will see quite a variance in how they get from flat to final flare shape… there isn’t one answer.

Cheers,
Andy

[robcat2075]

The brass used in instruments is chosen for being malleable and ductile. It can be greatly stretched without breaking.

It seems like they start with a flat disc that is only slightly wider than the finished bell.

I'm sure you've seen this video...



That's for a two piece bell. However I presume a one-piece could be spun on an even longer mandrel given enough time and skill.

[elmsandr]

For a one piece bell, it is a little different. Notice the various deformations in the material and how they are not completely random flower shapes.

https://youtu.be/hcVlISP-3ak

The video is for trumpet flares, but the idea is similar for their trombone flares.

Cheers,
Andy

[robcat2075]

For a one piece bell, it is a little different. Notice the various deformations in the material and how they are not completely random flower shapes.

https://youtu.be/hcVlISP-3ak

The video is for trumpet flares, but the idea is similar for their trombone flares.

That is interesting in that although the VO is asserting that every detail is crucial to "the Bach sound," the only aspect they claim a specific result for is the flare of the bell.

Every other element, like the thickness or the bead or the one-piece-ness just gets a hand-wave of ad-speak.

[brassmedic]

You should make a template of what you're trying to do before you order the brass. As said, it's the circumference of the bell, or an easier way to measure is diameter times pi. But the brass is going to stretch when you flatten out the seam, and the bell will stretch when you hammer it out, so you have to take that into account. If you're hiring someone to do the work, they should know this.

[elmsandr]

For a one piece bell, it is a little different. Notice the various deformations in the material and how they are not completely random flower shapes.

https://youtu.be/hcVlISP-3ak

The video is for trumpet flares, but the idea is similar for their trombone flares.

That is interesting in that although the VO is asserting that every detail is crucial to "the Bach sound," the only aspect they claim a specific result for is the flare of the bell.

Every other element, like the thickness or the bead or the one-piece-ness just gets a hand-wave of ad-speak.

Well, the video posted on YouTube by their marketing team wasn’t peer-reviewed for publication in a scientific journal…. We can’t agree if we can even hear these things, I expect the hand waving is all we’ll ever get and all we should get.

Processing wise, to make the thing round and mostly even, all the funny shapes are there so that the material is all being bent around in similar ways to even out the stretch.

Cheers,
Andy

[timothy42b]

Or, depending on what you're trying to do, maybe make a male sculpture of the inside of the bell, and do wet layup of fiberglas or carbon fiber on it, vacuum bag it, like the sail plane addicts do?

[TromboneSam]

Wow! So many great responses! Seeming like I'll have to do a lot more research.

I have taken some deep dives into the internet's annals of trombone and instrument making. Probably seen more videos than I know what to do with as far as trombone making, factory tours, live videos of horn makers shaping bells, etc. Read the few articles/documents/information sheets I could find about horn making.

I'm mostly curious about one-piece bells. I also am slightly curious about the flare portion of a 2-piece bell as well though.

Bell patterns vary widely depending on the desired shape/size, but also on the desired thickness profile. Basically the tail of the pattern is roughly as wide at any point as the desired circumference of the finished bell stem at that same point, plus the depth of the teeth for the brazed joint. But the shape of the flare portion and how much "wings" it has can vary a ton. The more wings/the more overall surface, the closer to an actual bell it will look once the back is "broken", and the least amount of stretching it will need, therefore the flare will stay ticker. A pattern with less wings will be more cone-shaped once opened up, and will need more hammering and more passes of inside spinning to get the flare formed. For the same bell size, less material means more stretching, which means a bell that gets much thinner towards the rim.

Tl;dr there is no direct correlation between the size of the finished bell and the size of the pattern.

I have considered most all of that, and I realize there is not a hard and fast rule for almost any of this. I guess my main question is about the minimum dimensions required for a sheet of material to be able to stamp a one-piece bell out of it. Of course, since the sheet would be a rectangle it'd probably make sense to try to get two bells out of it. Rough measurements are fine for now, but I guess I'm looking for a "safe" minimal amount of material to get since I'd hate to, for example, source a 22"x18" sheet to find I need 24"x16".

...you should have a design and a process plan for each step of the blanking, rough forming, folding, brazing, rounding, and spinning steps that define what the stock shape is before and after the process. If you don’t have a design and are just winging it, buy what you can get and have fun. Buy extra so that when you learn what doesn’t work you can adapt. Look up images of different bell makers, you will see quite a variance in how they get from flat to final flare shape… there isn’t one answer.

Cheers,
Andy

Am hoping to have a horn-builder do this part once I can source the material. Just don't want to ask too many questions and annoy them if the project ends up never even off the ground.

You should make a template of what you're trying to do before you order the brass. As said, it's the circumference of the bell, or an easier way to measure is diameter times pi. But the brass is going to stretch when you flatten out the seam, and the bell will stretch when you hammer it out, so you have to take that into account. If you're hiring someone to do the work, they should know this.

Word. So maybe a sheet of metal a little shorter in either direction than the finished product probably wouldn't be the end of the world. I guess a good question would probably be what can I expect as far as the variance, and what would be acceptable to bring to a builder/ask them to work with?

Or, depending on what you're trying to do, maybe make a male sculpture of the inside of the bell, and do wet layup of fiberglas or carbon fiber on it, vacuum bag it, like the sail plane addicts do?

This is an interesting thought, but seems like a lot of work for me to undo it and lay it flat just for a rough estimate of what the raw material dimensions would have to be

[elmsandr]

If you aren’t planning the process… don’t source the material. I’m guessing you are asking because you want something wacky. Cool. Maybe find a lead on a source, but the person designing the process is the one that needs to set the stock size.

Also, if it isn’t brass, the blank may need to be different as it will respond differently.

As a process engineer, lots of times when people don’t ask me for my process before sourcing material it just leads to buying new stock later to actually fit the process. If they want to stamp something, they will want a certain amount of overage. If there is no stamping, there is no need for that excess at that step… so you need the process that will actually be applied to answer. So, sure you can make bigger sheets smaller, but that may also be a pain. Plus, there are other requirements/standards e.g. hardness and flatness for how sheet stock is supplied. If you don’t buy this stuff for a living, you might not get what you actually want or need, you’ll get what you asked for.

So, what material do you want to try?

Cheers,
Andy

[TromboneSam]

If you aren’t planning the process… don’t source the material. I’m guessing you are asking because you want something wacky. Cool. Maybe find a lead on a source, but the person designing the process is the one that needs to set the stock size.

Also, if it isn’t brass, the blank may need to be different as it will respond differently.

As a process engineer, lots of times when people don’t ask me for my process before sourcing material it just leads to buying new stock later to actually fit the process. If they want to stamp something, they will want a certain amount of overage. If there is no stamping, there is no need for that excess at that step… so you need the process that will actually be applied to answer. So, sure you can make bigger sheets smaller, but that may also be a pain. Plus, there are other requirements/standards e.g. hardness and flatness for how sheet stock is supplied. If you don’t buy this stuff for a living, you might not get what you actually want or need, you’ll get what you asked for.

So, what material do you want to try?

Cheers,
Andy

Cool, all important things to keep in mind! I won't order anything until I have actual information in hand from the builder. I just wanna make sure I have the capital needed beforehand. I'd hate to be prepared to order material and then find out from the builder they need twice as much as I can afford.

I can't give too much away as the original idea is not mine, but it is a very experimental alloy for instrument making (never been done before, or at least never that has been reported on the internet or to instrument makers). The assumption is that it will function like most other alloys in the working process but who knows?

[Doug Elliott]

With most materials there is a minimum amount you will pay for, whether you get that much or not. Check that out before anything else, and whether it's even available in the thickness and size you need.

[hornbuilder]

A couple of things now that we have drilled down into this a bit..

Do you have a bell maker in mind? Have you asked them if they're interested/willing to do this project?

Your bell maker will have their own patterns to cut the sheet material for their bell mandrels. They will also know how big a piece of material is needed for the shape in question. You don't need to figure this out, they already have.

[timothy42b]

Or, depending on what you're trying to do, maybe make a male sculpture of the inside of the bell, and do wet layup of fiberglas or carbon fiber on it, vacuum bag it, like the sail plane addicts do?

This is an interesting thought, but seems like a lot of work for me to undo it and lay it flat just for a rough estimate of what the raw material dimensions would have to be

That wasn't my intent. I thought you were trying to produce a bell to your own design dimensions, and was suggesting that for the amateur builder a wet layup on a form is more doable than spinning or machining brass. If you're going to have a pro do the fabrication obviously this doesn't apply.

Presumably you have a drawing or formulas for the bell shape you want. Just calculate the square area, multiply by the proposed brass thickness, and from the density of brass you know the amount of material you need.

[hyperbolica]

This is an interesting thought, but seems like a lot of work for me to undo it and lay it flat just for a rough estimate of what the raw material dimensions would have to be

That wasn't my intent. I thought you were trying to produce a bell to your own design dimensions, and was suggesting that for the amateur builder a wet layup on a form is more doable than spinning or machining brass. If you're going to have a pro do the fabrication obviously this doesn't apply.

Presumably you have a drawing or formulas for the bell shape you want. Just calculate the square area, multiply by the proposed brass thickness, and from the density of brass you know the amount of material you need.

With modern CAD you can flatten out formed sheet metal with double curvature to get a decent approximation of the flat pattern. You could also figure out a nesting pattern if you were to make more than just a single bell from the same sheet. Since it seems clear you're not talking about a volume production run, this will be hand cut and formed. Tooling to stamp or trim would be overkill. Even using existing tooling, if you've got some really hard material, people might not want to risk damaging production tools on a one off.

[BGuttman]

...
Presumably you have a drawing or formulas for the bell shape you want. Just calculate the square area, multiply by the proposed brass thickness, and from the density of brass you know the amount of material you need.

I don't think the OP wants to start with a pile of brass shavings and roll out his starting sheet; more likely he wants to order a sheet of metal and lay out a pattern which will be formed into a bell. Once he knows what overall size piece he needs he can compare with available sheet sizes to order materials.

I would suggest a 2 piece design for a first try. Working out that mushroom shape for a 1 piece is tough.

Also, I think we generally use copper alloys for a number of reasons; mostly ease of forming and ease of joining. Other metals may create some problems with strength or brittleness. There's a reason nobody has come up with a steel or nickel instrument -- I'm sure it has been tried before.

[timothy42b]

I would suggest a 2 piece design for a first try. Working out that mushroom shape for a 1 piece is tough.

Yes. A cone would be easy but this isn't. I tried to do it with papier mache once and had a lot of trouble.

[elmsandr]

So you could mathematically figure it out… OR.. use a tailor’s tape measure to find a linear length from ferrule down the flare to the rim. Cut a handful of strings that length. Tape one end with the strings equally spaced for the ferrule circumference. Make a string the flare circumference. Equally space and tape the strings there. Play with it to try to keep them equally spaced for the entire length. Make the middle string completely straight and see if you can do it. See how close you can get. Remember to add a little extra to roll the rim and make the seam.

I’d probably do this on a poster board and mark up final flare dimensions at some intervals to transfer the strings to lines on the poster that look like a spiderweb.

A complete waste of time, but it could be fun to see how close you get to what is actually needed. Would also give you a nice visual of the bending minimally required.

Cheers,
Andy

[Doug Elliott]

I'm pretty sure the metal stretches quite a bit as it's spun and formed, so that method would end up about the right shape but too big. You need somebody with lots of experience doing this.

[brassmedic]

You should make a template of what you're trying to do before you order the brass. As said, it's the circumference of the bell, or an easier way to measure is diameter times pi. But the brass is going to stretch when you flatten out the seam, and the bell will stretch when you hammer it out, so you have to take that into account. If you're hiring someone to do the work, they should know this.

Word. So maybe a sheet of metal a little shorter in either direction than the finished product probably wouldn't be the end of the world. I guess a good question would probably be what can I expect as far as the variance, and what would be acceptable to bring to a builder/ask them to work with?

It mainly stretches the diameter. The width of your piece will probably be less than the finished circumference of the bell flare. As for the length, you start with a mushroom shaped piece of metal, and the length of your finished product is going to be roughly the distance from the small end to the edges of the dome shape. If anything, it might need to be a little longer than the finished product, because that dome shape is necessary for the bell rim to come out even. I really don't know how much it will stretch lengthwise. That's why it is imperative for you to have the dimensions of the template your bell maker is going to be using, such as this, although I think this is a historical trumpet pattern, so it would probably have much bigger "ears":

trumpet.jpg

If you're just making a wild guess as to how much the material will cost, I would guess the length of the finished bell and the width of the bell diameter times pi, minus 20%. For example, for an 8 1/2 inch bell, maybe 22 inches wide. Do not buy anything until you have someone for sure who has agreed to build it.