Belly vs Back Arching Asymmetry

[Mark Norfleet]

24 minutes ago, Marty Kasprzyk said:

I think that has deformed the normal way rather than a "strange way".

Agreed.  It appears to me that the top of the instrument is rotated toward the camera, giving the impression that the arch of the back is lower than that of the top.

[Peter K-G]

2 hours ago, Marty Kasprzyk said:

I think that has deformed the normal way rather than a "strange way".

 

1 hour ago, Mark Norfleet said:

Agreed.  It appears to me that the top of the instrument is rotated toward the camera, giving the impression that the arch of the back is lower than that of the top.

It is rotated towards the camera so that the back looks lower in height.

And you simply can't ignore this (as David B from A-A, pointed out it is educative)

I find it very interesting

This one (top) however is rotared away from the camera

But the back still looks lower. 

We can't tell from images how an old violin was to start with, but from looking at many many images of different old violins, it still looks like variations between top and back exists?

 

[Muswell]

2 hours ago, Peter K-G said:

You may have missed the meaning of my post

Ah yes, I think my brain was suffering fatigue after several hours of digging.

[Peter K-G]

4 minutes ago, Muswell said:

Ah yes, I think my brain was suffering fatigue after several hours of digging.

 

[Geigenbauer]

I am following this discussion and trying to learn.

Just wanted to point out that the STRAD 3D material has longitudinal CT scans of the three violins for comparison in the "image - 3violinsCT-compare" folder. These scans appear to be a bit off-center (the end pins are not visible). The top scan (not sure which violin it is) appears to show a bit of sinking at the bridge and maybe (?) some bulging?

[Dennis J]

Instruments that bend a lot under string pressure are the ones that distort the most.

They bend at or around the base of the sound post.

Downward pressure from the bridge holds the central area in place or depresses it a bit.

In this scenario it is is possible to assume the sides of the arching in the central area would bulge outward under compression while the central area is held in place by downward bridge force, or even sink further.

So nearly all distorting forces play out in that central area.

 

 

[Dennis J]

8 hours ago, Mark Norfleet said:

String tension.  Please do the suggested experiment.  Then, if it wasn't mentioned earlier (I've not read this entire thread) put a coin in the center of the paper to simulate downforce from the bridge and do it again.  At that point it should be completely evident.  If it's not you are, for some reason we cannot know, unwilling or unable to let go of your beliefs and open yourself to the possibility of learning.  

I've done a lot of experiments along those lines using carbon fibre. It very efficiently transmits distorting pressure.

But violin tops are not the same. Pushing down on the central area of a violin top will depress an area around that pressure point. The force distorts the surface in all directions, not longitudinally as you seem to suggest.

 

[Dennis J]

Looks like progress at last. Violins do bend under string pressure.

 

[Marty Kasprzyk]

If it didn't bend under string load it also wouldn't make any sound.

 

[Marty Kasprzyk]

I had forgotten that I had the attached finite element analysis of the static deformation of a violin from the string tension load done by Colin Gough.

Long term creep would make these deformations permanent. Influence of static tension and differential in-plane displacements breathing mode.pdf

[HoGo]

The photographs of arching from side are generally useless unless they are taken from long distance and for top/back separately aiming right at the plane of edges. But still there should not be excessive arch deformation from soundpost pressure that would show in the treble side view. Most pics I've seen are taken from short distance where parts of the arch get completely obscured by edges of bouts and often the background is cropped in a way that removes part of the actual wood as you can see in the examples posted in this thread.

[Bran Latebarie]

On 3/11/2021 at 4:21 PM, Marty Kasprzyk said:

If you wanted to prevent buckling and bending a good way of doing it is to avoid using any longitudinal curved arch and just use a straight extruded like cross arch like you see with corrugated metal sheets or one of my violas

My guess is that that design would be far too stiff.  It might make a good canoe paddle.

[Don Noon]

23 hours ago, Marty Kasprzyk said:

Long term creep would make these deformations permanent.

To be annoyingly picky, creep will introduce new permanent deformation, which is in addition to the static elastic deformation.  Sure, the creep is caused by the static forces and generally related to the static deformation, but they are different physics.

[JacksonMaberry]

Static Creep would be a good band name.

[Don Noon]

For a band of my generation, it would be Long Term Creep

[JacksonMaberry]

22 minutes ago, Don Noon said:

For a band of my generation, it would be Long Term Creep

[David Burgess]

1 hour ago, JacksonMaberry said:

Static Creep would be a good band name.

Isn't that already a music genre? 

[Marty Kasprzyk]

I've know some creeps for only a short time but I can predict they will be the same in the long term.

[Dennis J]

The exaggerated deformed shape shown in fig. 6.12 shows the back long arch stretched out and downward by sound post force.

The trouble with that scenario is that the maple backs of violins are made much thicker in that central area to prevent that happening. And the extra thickness is mainly achieved by having a flatter floor inside the back.

 

 

[Marty Kasprzyk]

Attached is an abstract of a report done on stress testing of the 1743 del Gesu "Cannone".  Apparently it bends when the strings are brought up to tension.

[JacksonMaberry]

Thin bits of wood bend under tension, moreso over time. More at 11. 

 

The extent to which a renaissance craft is over thought boggles the mind. Its not rocket science, full stop. 

[Bruce Carlson]

3 hours ago, JacksonMaberry said:

Thin bits of wood bend under tension, moreso over time. More at 11. 

 

The extent to which a renaissance craft is over thought boggles the mind. Its not rocket science, full stop. 

This study was necessary to collect firm data rather than relying on faulty intuition or hypotheses based on subjective opinions, such as we have been seeing in this thread. It's not a paper I necessarily need to improve my violinmaking. The diagram I find most interesting is the left hand diagram, second row down, which is the difference in measured deformation between the violin at rest without strings and the violin tuned to concert pitch. Each instrument, because of a whole series of factors, will move differently but, if it is a conventional violin, it will deform in a similar manner.

It was a concrete demonstration that a violin kept permanently tuned at concert pitch can and will deform and over time, as Don said, long term creep and permanent deformation can occur.

The study was aimed at better conservation methods for historical stringed instruments.

 

Edited March 17, 2021 by Bruce Carlson
Readability

[JacksonMaberry]

7 hours ago, Bruce Carlson said:

This study was necessary to collect firm data rather than relying on faulty intuition or hypotheses based on subjective opinions, such as we have been seeing in this thread. It's not a paper I necessarily need to improve my violinmaking. The diagram I find most interesting is the left hand diagram, second row down, which is the difference in measured deformation between the violin at rest without strings and the violin tuned to concert pitch. Each instrument, because of a whole series of factors, will move differently but, if it is a conventional violin, it will deform in a similar manner.

It was a concrete demonstration that a violin kept permanently tuned at concert pitch can and will deform and over time, as Don said, long term creep and permanent deformation can occur.

The study was aimed at better conservation methods for historical stringed instruments.

 

Sorry Bruce, my comment was not targeted at you or the study in question. I have only respect for yourself and your work. 

My post, however inflammatory, was a response to general trends in this thread and Maestronet writ large. I should have heeded what I was taught as a lad - "if you don't have anything nice to say..."

[reguz]

 It is for any maker to come to the understanding that the deflection of the instrument by string load pull the end blocks upward. In the investigation of the Canone violin places in a climate the end blocks are hold fixed clammed. The instrument while loading with a dead weight about 70% as if the structure becomes loaded by strings. Such technical arrangement pushes the center of the instrument and the back downward. This means the sound post moves. This condition is not possible producing on a "free" violin with string load conditions. There the end blocks move upwars/inward and deflection on arching shape will do different depending on the stiffness och belly and back together with the ribs looking at the upper and lower part. The figure above by B Carlson show that the end block do not move, hold equal level. On my internet site I have given my opinion on what is wrong, Read on www.zuger.se and "observation and consideration" http://www.zuger.se/images/20131112 Review on the Cannone violin investigation.pdf

B Carlsson liked to observe the deformation with 3D photo’ing the structure before and after string load. Their problem was that they decided that the end locks are fixed as they are in the climate box and the rib does not deform. We can see all this on the colored photos. We clearly see that the center moves down on their photos but THE BRIDGE FEET move in opposite direction. On a string loaded instrument the bridge move downward not upward. Understanding what they actually did has taken me many hours finding out. One need to read three different papers in consumption. B Carlson has great knowledge but the people he worked together with and did the 3D photo investigation do not know anything about violinmaking and structural function. Move the center down by the dead load in the climate box they believed is not different from loading the instrument with strings. Earlier on this site I show a complete investigation of deflection of the instrument, the master dissertation The sound post do not move, cannot move. If there would be a force that move the sound post means the instrument become heavier. In their case heavier in relation to the fixed end blocks in the climate chamber. I believe we all understand that this is a wrong assumption. Arching shape deformation of the violin for any eye is complex and impossible foreseeing how it may happen. This is why I did my investigation based on the geometry you are able to read about including thickness graduation. This is the very first time a geometric shaped instruments deflection has been investigated with real plate thicknesses. Read the master dissertation and consider. It may help you understanding better. Some very special structural condition named Straight Tangent Lines (STL) show that they do not deflect but in fact are stable resistant and function as rotating axes widening the instrument by the downward force on the C-bout side.

What this quality produces is Breathing by volume changes. In the dynamical state very important for sound projection.

[Bruce Carlson]

15 hours ago, reguz said:

 It is for any maker to come to the understanding that the deflection of the instrument by string load pull the end blocks upward. In the investigation of the Canone violin places in a climate the end blocks are hold fixed clammed. The instrument while loading with a dead weight about 70% as if the structure becomes loaded by strings. Such technical arrangement pushes the center of the instrument and the back downward. This means the sound post moves. This condition is not possible producing on a "free" violin with string load conditions. There the end blocks move upwars/inward and deflection on arching shape will do different depending on the stiffness och belly and back together with the ribs looking at the upper and lower part. The figure above by B Carlson show that the end block do not move, hold equal level. On my internet site I have given my opinion on what is wrong, Read on www.zuger.se and "observation and consideration" http://www.zuger.se/images/20131112 Review on the Cannone violin investigation.pdf

B Carlsson liked to observe the deformation with 3D photo’ing the structure before and after string load. Their problem was that they decided that the end locks are fixed as they are in the climate box and the rib does not deform. We can see all this on the colored photos. We clearly see that the center moves down on their photos but THE BRIDGE FEET move in opposite direction. On a string loaded instrument the bridge move downward not upward. Understanding what they actually did has taken me many hours finding out. One need to read three different papers in consumption. B Carlson has great knowledge but the people he worked together with and did the 3D photo investigation do not know anything about violinmaking and structural function. Move the center down by the dead load in the climate box they believed is not different from loading the instrument with strings. Earlier on this site I show a complete investigation of deflection of the instrument, the master dissertation The sound post do not move, cannot move. If there would be a force that move the sound post means the instrument become heavier. In their case heavier in relation to the fixed end blocks in the climate chamber. I believe we all understand that this is a wrong assumption. Arching shape deformation of the violin for any eye is complex and impossible foreseeing how it may happen. This is why I did my investigation based on the geometry you are able to read about including thickness graduation. This is the very first time a geometric shaped instruments deflection has been investigated with real plate thicknesses. Read the master dissertation and consider. It may help you understanding better. Some very special structural condition named Straight Tangent Lines (STL) show that they do not deflect but in fact are stable resistant and function as rotating axes widening the instrument by the downward force on the C-bout side.

What this quality produces is Breathing by volume changes. In the dynamical state very important for sound projection.

In the diagram I am referring to from the paper posted above, the violin was not clamped in any way and was resting on a red velvet blanket similar to a violin blanket from a case. First a computerized 3D scan was made of the entire instrument without strings. After this scan I set up the violin and tuned it to pitch (A 440). It was left thus for a time and every now and then it was retuned until the instrument stopped detuning and was therefore stable. At this point, a second 3D scan was made. The computer elaborated the data from the two scans to demonstrate the deflection of the tuned violin in relation to the violin when it was not subject to stress. 

As regards the feet of the bridge moving in the opposite direction, this is due to an error in the elaboration of the data by the computer. Where the bridge feet were sitting on the belly during the second scan it was, obviously, not possible for the 3D scanner to obtain a second measurement. Consequently the elaboration of the data in that area showed the bridge feet rising relative to the surrounding belly, which of course is impossible. The same problem was created where the tailpiece covered the belly but the data was smoothed in this area by extrapolating from the surrounding belly. I believe that they left the two bridge footprints only to show the position of the bridge. At any rate, the elastic deformation and/or deflection is relative to one's point of observation which in this case was not the soundpost that we cannot even see from the outside of the instrument.

      

Edited March 18, 2021 by Bruce Carlson
Readability