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Author Topic: How to tell how thick a bell is  (Read 2783 times)
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SethMatrix

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« on: May 17, 2015, 12:32PM »

How can you check how thick a bell is?
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« Reply #1 on: May 17, 2015, 12:49PM »

Ask it some hard questions  Eeek! Eeek! Evil Evil

Chris Stearn
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« Reply #2 on: May 17, 2015, 01:46PM »

Well, there you go!  :D
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« Reply #3 on: May 17, 2015, 01:47PM »

Using a thikness gauge, kind of millimeter caliber with an extendend arm. Something like this:

http://www.alibaba.com/showroom/metal-sheet-thickness-measure.html

http://www.mercateo.com/kw/dickenmessger%28e4%29t/dickenmessgeraet.html?switchToCountry=de&chooseGeo=true

There are gauges specially made for brass bells, with long and curved arms, those are very expensive. I have no idea where to get them - maybe Böhm in Germany or Ferrets in the US?

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« Reply #4 on: May 17, 2015, 01:58PM »

I imagine a decent set of digital calipers would do the trick.
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« Reply #5 on: May 17, 2015, 02:54PM »

I imagine a decent set of digital calipers would do the trick.

Not really.  You need to first reach around the bell wire.  After that, to get the correct measurement you need to be perpendicular to the tangent at the measured point of the bell curve, AND have clearance over the rest of the curve.

I like Chris' response best :)
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« Reply #6 on: May 17, 2015, 02:57PM »

Digital calipers won't work.  The bell rim gets in the way.

You have a problem trying to measure bell thickness.  You have a layer of lacquer or plating on top of the brass that must be compensated for.

You could probably use a 0-1.000" (0-25 mm) micrometer since you can put the measuring part past the bell rim.  Still, you need to figure out how thick the lacquer coat is and remove that.  Or you could scrape off the lacquer where you want to do the measurement if you don't mind the spot on the bell (not recommended!).

I think you might be able to use a caliper if you create a gauge block: take a piece of metal that is thicker than the bell rim and small enough to lay flat against the bell.  Measure with the digital caliper.  Now place the gauge block inside the bell rim and measure the bell and gauge block.  Subtract the value of the gauge block from your result.  Nowhere near as convenient as a micrometer.

You will then need to find a conversion chart from thickness to metal gauge.
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Bruce Guttman
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« Reply #7 on: May 17, 2015, 03:10PM »

Using a thikness gauge, kind of millimeter caliber with an extendend arm. Something like this: http://www.alibaba.com/showroom/metal-sheet-thickness-measure.html
http://www.mercateo.com/kw/dickenmessger%28e4%29t/dickenmessgeraet.html?switchToCountry=de&chooseGeo=true
There are gauges specially made for brass bells, with long and curved arms, those are very expensive. I have no idea where to get them - maybe Böhm in Germany or Ferrets in the US?
Not having the speciality tool you could place a small block, having enough height to allow you're micrometer to clear the rim, on the outside of the bell and measure the thickness of block + bell then subtract the block thickness to get the bell thickness. This make do would be less accurate but might get the data you need.

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« Reply #8 on: May 17, 2015, 04:19PM »

Double ball end micrometer. Here is a closeup of the jaws:



Of course, this only works close to the rim, and doesn't allow for lacquer thickness.

I use a single ball end micrometer for measuring slide wall thickness so I can calculate bore size.
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SethMatrix

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« Reply #9 on: May 17, 2015, 07:29PM »

Not down to exact millimeters, just through tapping it I guess? I heard you can tap it and the sound it makes can tell you how thick it is?
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« Reply #10 on: May 17, 2015, 09:58PM »

Not down to exact millimeters, just through tapping it I guess? I heard you can tap it and the sound it makes can tell you how thick it is?
If you have years of experience, maybe - but there are many other variables that go into the "ring" of a bell when it's plunked. I could see someone like Steve Shires having a feel for how HIS bells should sound when he's done spinning them, and maybe even later in the manufacturing process.
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« Reply #11 on: May 17, 2015, 10:05PM »

The difference between thickest and thinnest is probably only about a millimeter anyway.

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« Reply #12 on: May 18, 2015, 04:01AM »

Calipers or verniers, like brake verniers are perfect, you could also use a thickness measurement machine like an elcometer or similar

What is it your trying to work out, or just curious

Steve
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« Reply #13 on: May 18, 2015, 04:40AM »

The difference between thickest and thinnest is probably only about a millimeter anyway.


Far less, actually. The design space for thickness is very narrow. With actual measurements, the difference between thickest and thinnest was about 0.010", or about .25mm.

Tapping? Ha. Even if a person with a lot of experience and skill thinks they can tell thickness that way, I'd bet real money that they can't find one out of five repeatedly. Now, that isn't to say that they can't gage something far more important than thickness. Thickness may not be the most critical variable, particularly when comparing different manufacturers.

Cheers,
Andy
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« Reply #14 on: May 18, 2015, 05:26AM »

With underground storage tanks we measured thickness with an ultrasonic gauge. 

(You need to know if you have thin spots that might leak.) 

http://www.amazon.com/Flexbar-15945-Ultrasonic-Thickness-Gauge/dp/B001CTJP04#product-description-iframe
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« Reply #15 on: May 18, 2015, 05:52AM »

In the fiddle business, nonferrous plates (spruce and maple) a few millimeters thick can be measured nondestructively with a magnet/spring arrangement, to a precision of a tenth of a mm or so, IIRC. Search for Hacklinger. I don't know if anything similar exists for brass or bronze in gauges appropriate for bone bells.

Around string instruments, tap tones are very useful. They don't tell us a lot about thickness itself, but more about balancing various parts to each other, and finding subtle discontinuities in vibrating structures. Tapping is also a quick way to find weak joints. Oddly enough, a cold hide-glue joint works (or doesn't) a bit like a cold solder joint.
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SethMatrix

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« Reply #16 on: May 18, 2015, 06:01AM »

Calipers or verniers, like brake verniers are perfect, you could also use a thickness measurement machine like an elcometer or similar

What is it your trying to work out, or just curious

Steve
I just wanted to find out how thick this Bach 50 bell is, the horn itself is quite light, but it doesn't get too nasty in the loud dynamics.
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« Reply #17 on: May 18, 2015, 06:43AM »

In the fiddle business, nonferrous plates (spruce and maple) a few millimeters thick can be measured nondestructively with a magnet/spring arrangement, to a precision of a tenth of a mm or so, IIRC. Search for Hacklinger. I don't know if anything similar exists for brass or bronze in gauges appropriate for bone bells.

Around string instruments, tap tones are very useful. They don't tell us a lot about thickness itself, but more about balancing various parts to each other, and finding subtle discontinuities in vibrating structures. Tapping is also a quick way to find weak joints. Oddly enough, a cold hide-glue joint works (or doesn't) a bit like a cold solder joint.
A tenth of a millimeter is the difference between a heavyweight bell and a lightweight bell in some manufacturers.  It really is that small of a difference.

For the second part, yes this is very important.  Tapping is a great way to find cracks or incomplete joints.

Cheers,
Andy
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« Reply #18 on: May 18, 2015, 08:55AM »

>Elcometer:

An Elcometer would be good for measuring the thickness of the lacquer, but not of much use for the thickness of the brass.  Not too many folks own one (although I happen to, used it to measure solder mask thickness).

For Seth, if there is a metal shop in his school he might want to ask the teacher to use a micrometer on his bell.  Buying a micrometer, especially a good one, for this single measurement is a great waste of money.
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Bruce Guttman
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« Reply #19 on: May 18, 2015, 09:21AM »

keep in mind that especially on a one-piece bell, the thickness may vary considerably from the end where you'd be able to measure  to further down at the throat and stem of the bell.
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