Machining a bell for better tone

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Doug_Edwards
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Re: Machining a bell for better tone

Post by Doug_Edwards » Fri Aug 28, 2020 2:03 pm

Glenn,

I suspect that your bells lack of "carry" or ring is probably due more to the casting than the shape. If the bell was not fed properly in the casting process, you will have a dull thud rather than the bell ringing. The material could also have an effect also.

I have seen cast unmachined bells ring nicely, btw.

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Doug
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Howard Gorin
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Re: Machining a bell for better tone

Post by Howard Gorin » Wed Sep 02, 2020 10:29 am

Bell bronze is 80% Copper, 20% Tin, nothing else. Some people think that adding Silver makes for a sweeter tone, nonsense!
Absolutely no Lead. Many bronze alloys contain some lead. If your bell contains any lead, forget melting it down and recasting it as another bell.
Bell Bronze is expensive, brittle and not very machinable.
I have cast some 1.5" scale bells in real Bell Bronze, they sounded very well. I hope to make more someday.

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Dick_Morris
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Re: Machining a bell for better tone

Post by Dick_Morris » Fri Sep 11, 2020 5:28 am

have cast some 1.5" scale bells in real Bell Bronze, they sounded very well. I hope to make more someday.]
Howard, your note prompted me to give it a try. I had some time and copper. I had several pounds of scrap copper. My Consolidation will need a bell, but it's an unusual design and will mount about 1/3 of the way down on the side of smoke box, so if I want one I'll have to make my own. Fortunately, I have a prototype drawing to work from. While I'm at it, I"ll also make a replacement bell for my CP-173. It has one the same size as the Consolidation with a nice cast frame, but the bell itself is spun brass and looks a little cheesy.

This is an investment casting with the "wax" printed on the 3D printer. It's just shy of 2" diameter. The camera makes it look rougher than it is, but I did have some problems with the investment. It should clean up nicely, though. I'll see if I can improve on it next week after I get some more investment.

It isn't very loud and I suspect that scaling the prototype made the walls thicker than they should be. I have found that the sound improves as I smooth the inside and outside surfaces.
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Bill Shields
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Re: Machining a bell for better tone

Post by Bill Shields » Fri Sep 11, 2020 6:03 am

Made from copper?
Too many things going on to bother listing them.

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Dick_Morris
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Re: Machining a bell for better tone

Post by Dick_Morris » Fri Sep 11, 2020 1:40 pm

80% copper, 20% tin.

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Bill Shields
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Re: Machining a bell for better tone

Post by Bill Shields » Fri Sep 11, 2020 1:58 pm

many of the large (and small) church / carillon bells that I have seen (heard) are un-machined - many were cast long before the first lathe existed.

as you suspect...tone can often be a function of 'wall thickness'...which to us is 'stick in lathe' but 500+ years ago was 'get the sand in the correct place before you pour 2+ tons of molten metal...and if you get it wrong 'off with your head!'

puts an entirely different perspective on things.

stop to think about how they heated and poured such volume(s) of metal before they had really large furnaces and / or cranes.

Think about the Czars bell, which weighs best part of 500,000 # - even with a big chunk missing out of it.
Too many things going on to bother listing them.

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Fender
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Re: Machining a bell for better tone

Post by Fender » Fri Sep 11, 2020 3:00 pm

I recall reading about how many church bells in Europe were cast, hundreds of years ago. It involved the whole community and multiple furnaces, to provide sufficient fuel and capacity to melt the quantity of metal required.
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Re: Machining a bell for better tone

Post by Glenn Brooks » Fri Sep 11, 2020 3:17 pm

Dick_Morris wrote:
Fri Sep 11, 2020 5:28 am
I have cast some 1.5" scale bells in real Bell Bronze, they sounded very well. I hope to make more someday.]
It isn't very loud and I suspect that scaling the prototype made the walls thicker than they should be. I have found that the sound improves as I smooth the inside and outside surfaces.
Dick, there are some interesting on line descriptions of bell thickness, and shape. Apparently there are 5 or 6 zones to each bell, each having a distinct frequency. Hence each zone gives off a unique harmonic sound than can either complement or detract from the ringing tone of each bell. The thickest “zone” is the area of the flare around the bottom of the casting, then the walls taper out to a thinner cross section. The finest bells reverberate for seconds to minutes after each strike with the clapper.

I still haven’t found any advice how to actual machine the wall thickness to achieve optimum sound, except that foundaries that cast bells, do all the machining on the inside of the casting. And one photo shows a guy using a hand held grinder with large flap disk of some sort to shape the interior walls.

I’ve concluded my 116 yo bell doesn’t have the proper copper/tin consistency, hence clunks, rather than rings, when stuck... alas.

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Dick_Morris
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Re: Machining a bell for better tone

Post by Dick_Morris » Fri Sep 11, 2020 5:30 pm

There was a typo in my post, instead of "I had some time and copper. I had several pounds of scrap copper" It should have said
"I had some tin and several pounds of scrap copper." A few weeks ago my next-door neighbor was cleaning out some of the stuff his dad had collected and he gave me three one-pound of sticks of tin that I used to alloy with the copper.

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gwrdriver
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Re: Machining a bell for better tone

Post by gwrdriver » Fri Sep 11, 2020 5:48 pm

Howard Gorin wrote:
Wed Sep 02, 2020 10:29 am
Bell bronze is 80% Copper, 20% Tin, nothing else. Some people think that adding Silver makes for a sweeter tone, nonsense!
Actually, many people, or so it was believed. An ancient tradition was to toss a silver coin into the flask for just that reason. It probably made little actual difference.
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Bill Shields
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Re: Machining a bell for better tone

Post by Bill Shields » Fri Sep 11, 2020 6:45 pm

Fender

Exactly. I have a very good friend who is Russian ...is very knowledgable on the process..and works for an induction heating company. Go figure
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Greg_Lewis
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Re: Machining a bell for better tone

Post by Greg_Lewis » Fri Sep 11, 2020 9:20 pm

Here ya go. Modern Locomotive Construction 1892, by J.G.A. Meyer, pp. 514 – 516
Complete cross section with necessary math:
https://archive.org/stream/modernlocomo ... 4/mode/1up
Opera Snapshot_2020-09-11_191254_archive.org.png
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