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Anthony Panke

Non flatness of plates

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I can’t help noticing  when looking at the alard amati poster, that the back arching height differs when measured from the long arch , to when measured from the central cross arch. 17 to 15mm

 this is caused by non flatness of the rib structure due to warping, isn’t it?

which arch is more reliable?

how can I resolve this problem?

 

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Yes, it’s due to longitudinal warping. The cross arch height is usually more precise, but for sure also not in the shape as it was before the string tension began.

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11 hours ago, Anthony Panke said:

which arch is more reliable?

Does it matter?

After a few centuries, who is to say what the original arching was when it came off the maker's hands.

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No, but we can attempt to recreate it by observing the wood structure , typical stress deformations and the intent of the maker. I’m just interested in how one would model archings from non flat plates

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2 hours ago, Melvin Goldsmith said:

The truth is that most of these posters are crap.

As you sense the plates never sit on a flat perimiter. 

The Cecil Strad poster's arching patterns are useless; however, the photos are superb.

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Roger Hargrave wrote some interesting comments on those measurements in the Guarneri book. It is caused by warping in certain areas. 

Technically, you can of course put the arching patterns together and copy all deformations. It is the question of this makes sense. I personally have massive doubts that this makes better instruments. At an extreme level makers are using a plaster cast of an original (with all the deformations caused in a time span of 200-300 years) and chalk fit a new top and back into it. While the result can be of course visually quite stunning, it doesn't reveal any deeper insight into how the original archings were designed and carved from a log of wood. 

 

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16 hours ago, Anthony Panke said:

how can I resolve this problem?

None of the arching patterns is 'reliable'. 

The solution is not to take them as they are. I have doubts as well that the old makers tried to 'control' the arching in the same we are doing today. Perfect control makes only sense if the structure won't change even over a time span of 300 years. We are not working with metal. As a matter of fact many aspects in violin making got the aspect of metal work. Most of the measuring devices a modern luthier is using were invented to work with metal. Calipers measuring to 1/10 mm are from the beginning the wrong tool. Measuring lengths and widths in millimeters is producing only  confusing nonsense numbers. 

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The problem for less experienced makers is you need to start somewhere with arching guides. I would venture that even some makers that are experienced are guessing on how to manipulate the arching. Just carving by the seat of your pants seems leaving a lot to chance in a very important variable.

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3 hours ago, Anthony Panke said:

Wouldn’t this mean that contours of height above the rib surface would be more accurate, assuming one corrects the deformations?

If you assume that those makers of old carved perfect symmetry. I don't believe they did.

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