Machining a bell for better tone

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Glenn Brooks
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Machining a bell for better tone

Post by Glenn Brooks » Sun Aug 23, 2020 2:37 pm

Hello all,

I have an old 4” bronze bell that has a very flat tone. It goes thunk, thunk, thunk, rather than ding, ding, ding.

Years ago I read one must machine the flare of the bell in some way to get a good tone.

Any suggestions how to do this properly?

I don’t know what the metal content of the casting is - it was poured in 1903 by a very experienced RR Machinist and early day miniature train vendor. Also thinking maybe needs a new, heavier, steel clapper...

Thanks for any suggestions or best practices.

Glenn
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Bill Shields
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Re: Machining a bell for better tone

Post by Bill Shields » Sun Aug 23, 2020 3:11 pm

you might want to ask Pass and Stow
Too many things going on to bother listing them.

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Builder01
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Re: Matching a bell for better tone

Post by Builder01 » Sun Aug 23, 2020 3:39 pm

In the photo, it almost looks like the bell is touching the bracket. Make sure the bell does not touch anything except where it is attached at the top. A leather washer between the bracket and the bell with let it ring better. Also, look inside the bell. It should be smooth and symmetrical with no lumps or bumps. Also make sure that when struck, the clapper gets away from the bell to allow it to ring freely.

The material of the bell is not so I important, although bronze and brass will ring best. Even steel and aluminum will ring well if all the other factors are correct. I remember in marching band, the bell bars were made of aluminum and when struck with a metal or hard plastic beater, they would cut like a knife!

hptwin
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Re: Machining a bell for better tone

Post by hptwin » Sun Aug 23, 2020 4:47 pm

Glenn,
Long ago when the Penn Central catastrophe was being auctioned off I bought several large steam locomotive bells that had been stored at the Juniata Shops. All the bells sounded beautiful except for one that went very definitely "Thunk". Upon close examination it was observed that a hairline crack extended from the bolt hole for the clapper to the rim. This was enough to completely destroy the sound. You could try dye crack detector and powder developer.
As Bill suggested, get in touch with Pass and Stow or their successors for some advice.
My understanding of bell bronze is that the alloy is very important. Bell bronze has a very high tin content, making it very hard and, therefore brittle. The ideal mix seems to be to make it as hard as possible without cracking. I believe that good bell bronze is as brittle as good cast iron, though I have not had the heart to take a sledge hammer to my cracked Pennsy Bell.
Check for cracks, but it may just be poor mix of bell alloy. You could experiment with the shape of the inside of your bell. Every bell that I have seen has been machined inside and out. Somewhere on the internet in Google images there is a Baldwin Works drawing of a bell cross section with all the different wall thicknesses and curve radii. Maybe that would give you some guidance on proportions to help you rework your bell. I have seen two apparently identical bells where one sounded clear and sweet and the other sounded sour and muddy. I believe bell making is truly an art, not a science.
My last idea is to keep a photo of your bell on your phone with the dimensions of the mouth, the shoulder, or top and the height
from rim to crown. Whenever you visit an antique or junk shop look for bells and ring them. You never know, you may get lucky and find one that sounds as good as it looks.
Best regards, Mike

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Re: Machining a bell for better tone

Post by kcameron » Sun Aug 23, 2020 8:37 pm

I would be inclined to take the bell out of the bracket. I'd make a non-metal hanger (like wood or string) around the top connection. I'd then try tapping the bell with a few different objects (metal, plastic, wood, etc...) and see it it rings differently. Also does the tone change as you move the point of strike around the bell. I would have the clapper removed during this testing.

Depending on what you find may say that you never get a good tone under any condition or that some give a good tone. Then focus on what's different between the good and the bad.
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Glenn Brooks
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Re: Machining a bell for better tone

Post by Glenn Brooks » Sun Aug 23, 2020 11:57 pm

Thanks guys, I’ll try hanging the bell independently of the mount and see how it sounds. I did remove it today and strike by hand. Still sounded muddy and dull. Also, I’ll make a leather washer and see how that affects the sound.

Also will look for cracks. So far, don’t see any. But some brass polish and a little buffing won’t hurt.

The inside of the bell is definitely rough and unmachined. Also the casting is almost 1/4” thick. So wondering if the thickness of the casting itself has something to do with the tone?

As an aside, I picked up a similar sized, highly embossed bell, at a local antique shop last year. It rings bright, loud and clear with a simple stroke of the clapper. But it looks like a small 4” prayer bell that came out of possibility a Himalayan Monastery. Lots of intricate inscription and casting embellishments on the outside. Isn’t really suited for a locomotive, and I don’t want to destroy the character of the bell, itself without knowing more about it. The bell is half the thickness and sounds outstanding. Maybe be good Karma to just use it, Instead!

Glenn
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SteveM
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Machining a bell for better tone

Post by SteveM » Mon Aug 24, 2020 8:12 am

Bill Shields wrote:
Sun Aug 23, 2020 3:11 pm
you might want to ask Pass and Stow
Definitely not. Those guys are cracked!

Steve

Glenn Brooks
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Re: Machining a bell for better tone

Post by Glenn Brooks » Mon Aug 24, 2020 12:56 pm

Haha, ok, I think I get it now... maybe... after some google research I discover that Pass and Stow have now become the beer gardens along third base at the Philadelphia Phillies stadium. Good a place as any to consider getting cracked.

I found only two bell foundries that still do harmonic balancing of bell castings - aside from Tibetan Monasteries, who do not do internet advertising or you tube videos of their work. A bell with an unmachined inner surface is called a “maiden bell”, and has little or no tone. Apparently, that is what I have.

To, achieve an acceptable ring tone, the inside diameters of bells are machined to different thicknesses along five different meridians, or vertical zones comprising the body of the bell. Each meridian having its own unique frequency response and material thickness. The thicknesses are apparently a secret. And, further, the primary oscillation of the flair of the bell interacts with the frequencies of the other regions to produce a multi part harmonic - the bell tone - that should last for several seconds or more.

And, after all that, if the bell, doesn’t sound right, they take a hammer to it and break it up into little brass bits and throw it back into the pot to melt and do all over again.

So I’ve narrowed down my choices for tuning my bell to writing two emails to the last two bell foundries in the world who machine bells, or writing a stamped, self addressed letter to a Tibetan Monk. Given the postal delays, Iam hoping to receive a reply from Lhasa in late February.

Glenn
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vlnmkr
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Re: Machining a bell for better tone

Post by vlnmkr » Mon Aug 24, 2020 2:03 pm

I assume one of the foundries is Grassmayr in Innsbruck. They have been around since 1599. They are located in Wilten across the station for the Stubaitalbahn. www.Grassmayr.at. I used to have a contact 45 yrs ago. Don't know any one there today.

M. Becker
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Glenn Brooks
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Re: Machining a bell for better tone

Post by Glenn Brooks » Mon Aug 24, 2020 2:28 pm

M. Becker, did not know about Grassmayr, but Thank You. I’ll send them a message, see what they say.

If would be actually be great to have this bell tuned up, if the cost isn’t to high...

Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

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tetramachine
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Re: Machining a bell for better tone

Post by tetramachine » Mon Aug 24, 2020 3:16 pm

This post reminds me of a story my grandfather told me. His dad was a building manager of the town hall in a small town in Germany.

As such he hired the guys that rang the bells in the town's bell tower. One day a guy shows up in reply to a job opening for a bell ringer. Problem is the guy has no arms, how can you ring the bells with no arms he is asked.

I just use my head to ring the bell. So they go into the top of the bell tower, to show how good he is.

Guy runs full tilt and smacks the bell 12 times with his head. Impressed the guy is hired. The guy worked for years ringing the bells in the tower.

One morning the police come to .my great gramps office, and ask him to come outside. There laying on the ground is the body of a man, with no arms. The police as if he knows the guys name, no he responds, but his face does ring a bell.
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Bill Shields
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Re: Machining a bell for better tone

Post by Bill Shields » Mon Aug 24, 2020 7:54 pm

willing to bet that if you can talk to one of the guys at Malmark or Schlumerich (sp?) you could get some really good advice...from people currently in the business and know what the internet is all about.

Pass and Stow are a bit like Harlan and Wolff..besides bells that crack and ships that sink..

who knows them for anything else? :shock:
Too many things going on to bother listing them.

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