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Belly vs Back Arching Asymmetry


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There is a very broad range in the historical examples.  

To point to the fact that arching made wtih a modern through curved top arching can be pushed and distorted to aquire characteristics resembling classical top arc shapes is not equal to claiming the actual old arch shapes start significantly different in character than as they are seen today.

And, pointing to the failure of some modern examples made too actually flat is not equal to claiming that the actual old arches, with their slight crowning through the flattish area, would also have failed.

To claim that distortions are they main or only reason for the shape of all the old arches, you need to demonstrate that all versions of these classical arches can be reached by the mechanism you point to.

Nothing said or shown so far does this, not remotely.

And again, there is no cause to not believe the shapes weren't carved with basically the same characteristic shapes we see today.

You have not demonstrated any reason to disbelieve that straightforward and obvious, the makers carved basically what we see.

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13 minutes ago, David Burgess said:

Were it not for the downforce at the bridge. ;)

Here's a simple experiment for you: Lay a piece paper flat on a table. Push the ends together. You will get an arch. Then push down at the center. The center will come down, and regions closer to the ends will bulge.

I'm find it amazing that some people don't seem to grasp even some of the most simple mechanical principles.

In 2D, the distortions you claim are reasonable.

Probably that's why you manage to hang on to your unfounded belief.

But in 3D, the distortion you claim are not reasonable nor sufficient to explain the range of historical examples.

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33 minutes ago, David Beard said:

You have not demonstrated any reason to disbelieve that straightforward and obvious, the makers carved basically what we see.

Please re-read the last thread having to do with this topic, before re-repeating all your re-redunancy, which was also sourced in your poor reading comprehension.

Here's the link to that thread, for your re-perusal: ;)

https://maestronet.com/forum/index.php?/topic/348012-long-arches/

 

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Ditto.

Rather belittling, please recognize that we disagree.

I have presented an hypothesis that is simpler than yours.

You have presented an hypothesis.

I do not think you have presented cause for resorting to your more comlicated hypothesis.

I do not think you have presented sufficient evidence to claim your hypothesis is viable, so I discount your hypothesis as very unlikely.

But, in the prior thread, I also gave list of additional points which, if demostrated, would support tye viability of tiur hypothesis.  You have simple evaded those points rather than adress them.

Can we truce for now? Both of us need to collect some more decisive new evidence over the coming several years.  Until then, neither of us is going convince the other.

I do take your hypothesis seriously, and I also acknowledge that my position is still only a hypothesis.  But I don't believe you have established either the need or the viable or the actuality of your hypothesis as well as you believe you have.

For now, that's the most acknowledgement I can give to your hypothesis.

Might we table the issue for now?

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23 hours ago, David Beard said:

The amounts of movement needed at the ends and bridge to produce the shapes seen would be more than anything justifable by observation.  The directions are as you would like, but the amounts are not.  Not by a long shot.

I'm going to sleep so I will spill the beans...

Lengths of shown arches from top to bottom :

  • 351.768 mm
  • 351.752 mm
  • 351.744 mm
  • 351.466 mm
  • 351.154 mm

(Notice horizontal straight distance from crest of edge to other crest is 350 mm)

So the difference between flat distance and fullest arch is bare 1.768 mm, and difference between the two most different arches as compared in sixth arch is mere 0.6mm (the distance between the two is 2.5 mmin the bouts). Not a very long shot, IMO. Most violin makers don't even measure violins with enough precision to detect such movement between endblocks. But the rising of bouts is evident proof that this happens.

Adding the picture again...1981527774_Longarch.thumb.png.69ba4896834ed8ca58d0ed2689e8d9ba.png

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4 minutes ago, HoGo said:

I'm going to sleep so I will spill the beans...

Lengths of shown arches from top to bottom :

  • 351.768 mm
  • 351.752 mm
  • 351.744 mm
  • 351.466 mm
  • 351.154 mm

(Notice horizontal straight distance from crest of edge to other crest is 350 mm)

So the difference between flat distance and fullest arch is bare 1.768 mm, and difference between the two most different arches as compared in sixth arch is mere 0.6mm (the distance between the two is 2.5 mmin the bouts). Not a very long shot, IMO. Most violin makers don't even measure violins with enough precision to detect such movement between endblocks. But the rising of bouts is evident proof that this happens.

Adding the picture again...1981527774_Longarch.thumb.png.69ba4896834ed8ca58d0ed2689e8d9ba.png

Again, in 2D the idea appears viable.

But, in 3D, the extra height at the ends also affects the cross arching.  How do they get broader?  And, why aren't the angles in the channeling more effected.

Since the claim is that ALL classical examples went through various degrees of similar distortions, ALL the chanelling should be skewed at the extremes of the bouts.  So, why don't the examples show that?

Also, if the plates are just deformed, why does fairly significant pushing in or pulling out of a free plate at the ends yield similarly visible degrees of enhanced and reduce temporary distortion?

A limited 2D exploration makes an enticing case for the hypothesis.

But trying to get from that to explaining the full range of classical examples and the associated details in 3D doesn't come so easily.  And, at least until further evidence, I don't believe it comes at all.

Nor does it need.  Even if some day you demonstrated viability for the hypothesis, that still doesn't mean that's what happened.  Nor would it automatically mean they didn't simply carve those top arches essentially as we see them.

Presuming they carved something basically like what see remains the simpler and more direct and natural hypothesis.

 

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21 minutes ago, David Beard said:

Again, in 2D the idea appears viable.

But, in 3D, the extra height at the ends also affects the cross arching.  How do they get broader?  And, why aren't the angles in the channeling more effected.

Since the claim is that ALL classical examples went through various degrees of similar distortions, ALL the chanelling should be skewed at the extremes of the bouts.  So, why don't the examples show that?

Must be “liberty at the margins”

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2 hours ago, David Burgess said:

You've left out the bridge downforce in your thought model. :P

 

You are contradicting yourself here. In a previous post you said: "Don't forget that the compressive force, end-to-end is much higher than the bridge downforce."

I realise that the longitudinal force over the bridge is quite considerable but we are dealing with the whole arched body of the top strongly glued to ribs. How it distorts is anybody's guess.

 

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1 hour ago, David Beard said:

1. Rather belittling, please recognize that we disagree.

2. I have presented an hypothesis that is simpler than yours.

3. You have presented an hypothesis. I do not think you have presented cause for resorting to your more comlicated hypothesis. I do not think you have presented sufficient evidence to claim your hypothesis is viable, so I discount your hypothesis as very unlikely.

4. But, in the prior thread, I also gave list of additional points which, if demostrated, would support tye viability of tiur hypothesis.  You have simple evaded those points rather than adress them.

 

1. We do indeed disagree, so you've got that part right.

2. I disagree that your hypothesis is simpler than mine.

3. I really don't give a flying phuck what you think, nor do I have any expectation of convincing you. My motivation for posting my disagreements is so that other readers won't be deceived by bizarre claims which have been left unchallenged. If you posted that the best and fastest way to sharpen your plane blade is by dragging it on a rope behind your car, you can count on me disagreeing with that too. This would be entirely separate from trying to convince you of anything.

4. Nope. I think I addressed all your claims at least once. I probably failed to address them each and every time they were repeated, the repetition of which suggested that you had failed to read what I had already written.

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15 minutes ago, Dennis J said:

1. You are contradicting yourself here. In a previous post you said: "Don't forget that the compressive force, end-to-end is much higher than the bridge downforce."

2. I realise that the longitudinal force over the bridge is quite considerable but we are dealing with the whole arched body of the top strongly glued to ribs. How it distorts is anybody's guess.

 

1. No, I haven't contradicted myself. Both forces (not just one) need to be integrated into the thought model, in order to get it to conform to real observations.

2. No, it is not "anybody's guess". The distortion patterns have more things in common than not, and are quite predictable, to one who has much experience in the restoration trade, and has been paying attention.

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1 hour ago, David Burgess said:

1. No, I haven't contradicted myself. Both forces need to be integrated into the thought model, in order to get it to conform to real observations.

2. No, it is not "anybody's guess". The distortion patterns have more things in common than not, and are quite predictable, to one who has much experience in the restoration trade, and has been paying attention.

The real observations you refer to are just that. And what looks odd or distorted can be explained largely by sinking forward of the bridge, which is probably the weakest part of the top's arching.

If you take that sinking away there is no reason to believe that the long arch was not carved that way.

I'm inclined to think that the whole violin body bends upward at each end under string tension/compression and that would most likely manifest itself at the weakest part of the body, namely the waist area. And that would explain sinking of the top in that area under bridge pressure, becoming a permanent characteristic over time.

To take this further I would say that the downward buckling forward of the bridge evident in photos might be matched by upward buckling in the area  behind the bridge between the sound holes in the area of the lower corners.

 

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If one has looked at a lot of violins it is pretty easy to see that there are some instruments which look as if they have not distorted much from their original shape and others which appear to have distorted from those  same shapes to something lower in the center and rounder at the ends. Differences in the amount of distortion can be explained by strength differences in the wood, graduation, amount of use and climate. 

 Instruments made too large , too flat or too thin can exhibit these distortions in a very few years as well as those subjected to extreme humidity.

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38 minutes ago, nathan slobodkin said:

If one has looked at a lot of violins it is pretty easy to see that there are some instruments which look as if they have not distorted much from their original shape and others which appear to have distorted from those  same shapes to something lower in the center and rounder at the ends. Differences in the amount of distortion can be explained by strength differences in the wood, graduation, amount of use and climate. 

 Instruments made too large , too flat or too thin can exhibit these distortions in a very few years as well as those subjected to extreme humidity.

I have no argument with this.

It is the further claims that the instruments started with modern type through arched tops and transformed from that into what we see today.

To me, that is unsupported fantasy.

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Someone said, "I'm find it amazing that some people don't seem to grasp even some of the most simple mechanical principles."

As a mechanical engineer who has done his fair share of finite element deformation models, I agree - but not necessarily in the way you mean.  :D

The bottom line is the deformations are complex, in multiple directions, not just one.  But with some basic thought you can rank the first order effects.  Bridge compression is significant, end folding is not.  The f holes tend to concentrate bridge deformation in the center of the plate so "bulging" is not heavily driven by the bridge.

Conclusion is that instrument profile have BOTH intentional design changes in the arching and deformation.  I don't see why this should be controversial.

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5 hours ago, David Burgess said:

Were it not for the downforce at the bridge. ;)

Here's a simple experiment for you: Lay a piece paper flat on a table. Push the ends together. You will get an arch. Then push down at the center. The center will come down, and regions closer to the ends will bulge.

I'm find it amazing that some people don't seem to grasp even some of the most simple mechanical principles.

I tightened my belt but this just split my bulge in two.

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In looking at the scale of the images of actual deformation , posted by Davide Sora in the previous discussion,it seems the upper and lower bouts bulge out about the same amount as the bridge area is pushed in. How many mm deformation have the bridge areas of classic instruments undergone and wouldn't that many mm of upper and lower bout bulging illustrate the David Burgess theory perfectly.

"This image refers to a violin a few moments after being tuned to 440Hz, I don't know if it's a good or bad one and obviously the numbers will change from violin to violin, but the areas will be more or less the same."

408273665_Deformazionicontensionecorde.thumb.jpg.3af147ae9d75b50b5c46436972ec16be.jpg

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For bulging to occur at the upper and lower bouts the height of the arch in those two places would have to rise in relation to the plate's edge position.

So, is it bulging of the upper and lower bouts or bending at the waist?

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46 minutes ago, Dennis J said:

For bulging to occur at the upper and lower bouts the height of the arch in those two places would have to rise in relation to the plate's edge position.

So, is it bulging of the upper and lower bouts or bending at the waist?

Yes.   popcorn-and-drink-smiley-emoticon.gif.04c27446608fe21e086355f7a1e5a9c6.gif

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8 hours ago, David Beard said:

I have no argument with this.

It is the further claims that the instruments started with modern type through arched tops and transformed from that into what we see today.

That is not the claim, and your repeated failure to comprehend this is why we keep going in circles.

As I already stated in the other thread, we don't know what the original arching was. But what we do know, or should know, is the characteristic way in which tops distort with string loads. Is it possible that some makers 300 years ago copied archings from even older instruments which were already distorted, as some makers do today? Yes. Is it possible that  some makers started with a more peaked long-arch on the top than the back, anticipating from experience or training the way in which they would distort, rendering them with an arching more similar to that of the back years later? Yes.

Are you done now? :lol:

Please print this post, tape it to the wall next to your computer, and re-read it before posting another claim claiming that a claim is something other than it was. :D

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1 hour ago, reguz said:

Possible this master dissertation helps to understand structural deflection caused by string load

http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=9024959&fileOId=9024960

 

It's instructive to look at Figures 6.11 and 6.12, on page 76 of that paper.

"Figure 6.12: Deformed shape of the pre-stressed violin box with the deformations scaled by a factor of 100."

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