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plate flexing question


jim mcavoy
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Presumably you are asking about flexing free plates during the build process.

 

The makers who I've seen using the flexing method have all been around for a while and made LOTS of violins, and developed a feel through that extensive experience.  

 

When I was in the aerospace biz, where weight was critical and I had to weigh lots of parts, I could come quite close to guessing a weight by just holding it.  A technician demonstrated his ability to tighten a bolt to a specified torque by feel alone, after having years of experience using a torque wrench.

 

I don't think it is something you can read about and learn.  A pro might help you learn more quickly by hands-on training.  

 

As to whether it's a great benefit, who knows... there are plenty of good makers who don't use this method.

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Well to me this is a way understudied "realm" of building, both in instruments and well pretty much anything else.These "skills" are what really make "craftsmen" Dons story about guessing weight is a good example.

 

Like an archer using an old wooden style long bow, knowing how and where the breaking point is, pulling the bowstring right to the max edge without breaking it,or any other tactile skill similar, perhaps being able to "feel" thicknesses, to eyeball  measurements/weights etc.These are things that are known things, but perhaps not really studied from a scientific view.

 

Plate flexing, understanding the elasticity, the recoil speed to which the plate returns to the un-flexed state, how all the various independent areas and the way they bend, in different direction of flex and how all these independent areas are actually part of the whole plate, and just what areas do we want flex and how much, are all very "not looked" at things imo, and I would hope someone like Don who has the methodology and understanding would someday put more effort or interest in this "direction of building.

 

If the goal was to make a violin that sounded close to a Strad. My theory is that if we could rip the Strad apart, after finding wood that is very close "numbers/properties wise"...And then analyze the ranges of motions in a 360 degree spherical way, and or flex the plate in every way possible and measure this,  then match this range of motion with our new plate/s, I have a feeling that you would have a very similar sounding instrument to the Strad.

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Mike Scoggins would hand me a plate and tell me to flex it and get that feeling in my hands. I use numbers, sometimes weight (in the beginning), but if it is to Sacconi numbers and it doesn't flex "right", or "feel right", I'll carefully continue.

 

And Don is correct, you just have to ask. It is, at present, a tactile thing. I have seen prominent mandolin makers who use a spring scale and weight to measure deflection under a load, with the goal of the top having a certain deflection at a certain weight applied.

 

A little help-or not-on tops. Mike taught me to graduate the top down to about 5mm, then cut the f-holes, then finish. His rationale was, "When are you ever going to get to flex an old violin top without f-holes?"

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Basically you are checking the rigidity of M5 (longitudinal flexing), M2 (transversal flexing) and M1 (torsional flexing).

Use them together with tap tones can help to figure out which bending strength corresponds to which  frequency.

You can also test the local bending in various location of the plates, complicating even further the understanding and learning of feelings.

For me quite unreliable without a lot of practice (and even with practice...), hard to feel small changes, a little better when used together with tap tones.

In any case I can not resist and I do too, I think it is in any case of some help and if one does not start never develop enough sensitivity.

 

An obvious warning, I have seen many open center joint from improper use of this technique by inexperienced makers.... ;)

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Never mind waves vibrations tap tones or weight.

When feeling a plate, you're asking yourself does it feel too thick or just right ? 
Too thin is not good....

Diagonal twisting in the hands is pretty much all I do. 
Putting the plate flat on the bench and poking it looks odd, to me. 

Bottom line, look that the wood you've got to use, and use it well. 
If using willow for a Cello back, leave it thick. 
Etc 

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I agree with Davide that corresponding tones can have a direct correlation to flex and stiffness and are useful when used together in reference to each other. My thinking is that when he says "hard to feel small changes" that a "contraption" a "rack" like device that could quickly and accurately measure ones arbitrary target range of flexibility could be developed and used to hit these targets.

 

Of course it's trying to find and prove that these ranges of motion "work" and or could simplify and standardize plate carving.

 

Well, admittedly, the only time I really "think" about building instruments is when I'm here theorizing out loud, normally when I'm actually building instruments, I don't really think about building instruments. I'm pretty much focused on not getting cut or setting myself on fire :lol:

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... My thinking is that when he says "hard to feel small changes" that a "contraption" a "rack" like device that could quickly and accurately measure ones arbitrary target range of flexibility could be developed and used to hit these targets.

 

I've actually been considering such a device for working bass tops. My experience with basses is that good sounding ones are much more fragile than a violin. Measuring the deflection under a load applied at the bridge area could be a useful gauge of when to stop thinning.

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I have been measuring absolute bending stiffness of violin plates for several years now, with the plate being supported at the edges and loaded at the middle... both along grain and crossgrain.

 

I don't see anything terribly enlightening in the data... about the same kind of help as taptones, but a little different.  

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An obvious warning, I have seen many open center joint from improper use of this technique by inexperienced makers.... ;)

Maybe they didn't give the Titebond enough time to cure ... :)

 

On a more serious note I am intrigued by these terms

 

Basically you are checking the rigidity of M5 (longitudinal flexing), M2 (transversal flexing) and M1 (torsional flexing)

 

Not so much the words (I understand what the words mean)... more the numerical designations ...M1, M2 etc ...

 

I have also seen B1, B0 referred to on the forum.... I likewise have no idea what these refer to.

 

Where does one go to learn about  this ? Googling it doesn't appear to be of any great help ...

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I have also seen B1, B0 referred to on the forum.... I likewise have no idea what these refer to.

 

Where does one go to learn about  this ? Googling it doesn't appear to be of any great help ...

 

http://www.catgutacoustical.org/research/articles/modetune/modechrt.html

http://www.schleske.de/en/our-research/introduction-violin-acoustics/modal-analysis/animation.html

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I have been measuring absolute bending stiffness of violin plates for several years now, with the plate being supported at the edges and loaded at the middle... both along grain and crossgrain.

 

I don't see anything terribly enlightening in the data... about the same kind of help as taptones, but a little different.

ERGO:

Stiffness is not the answer. It is more complicated than that.

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Flexing plates gives an experienced maker another guide in whether or not to take off another tenth or two or leave it the heck alone. If the numbers are a bit thicker than normal, the plate feels stiff and it weighs more than I like then it's a no brainer. If the plate feels stiff, the weight is already low and its already a bit thin then I figure it will be a nice bright fiddle and call it good. Conversely if the plate feels soft and light obviously I leave it thicker.

 

As I have said before my goal is to make instruments that are usable by most professional musicians but they only have to be loved by one. I'm not trying to get the same sound over and over.

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Not to be unnecessarily cryptic, but in my case that question comes into the same category as "Have you stopped beating your wife?". I will explain in due course, in a thread in the Maker's Gallery forum.

Your mindset or way of reasoning will need to show more discipline if you are to be successful at making a functional violin.  Notice I said violin and not vso. 

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