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ctanzio

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  1. Wood properties like the elastic moduli and yield/fracture points are affected by dynamic loadings, like strain rate. However, these are significant only at high strain rates typically seen during impact and blast events. Except for the occasional showpieces from composers like Wieniawski and Paganini, I doubt a violin will see such high strain rates.
  2. Dammar varnishes are more typically made by dissolving in turpentine or alcohol. Anything that does not dissolve is thrown away. Dammar in turpentine can make a very clear, high quality varnish that dries hard. You might be able to get it to combine with linseed oil by by first dissolving it in turpentine in a ratio of 4 turpentine to 1 dammar by weight. Discard whatever has not dissolved. Then add 1 part linseed oil. Like all anecdotal recipes, your mileage may vary. Also, turpentine is a bit toxic and many find its odor to be obnoxious. You might want to try a resin that is more compatible with linseed oil.
  3. To give an example to reinforce Don's comment about the difference between deflection and stress: Consider a cantilever beam fixed at one end, i.e., a beam sticking horizontally out of a wall, and subject to a point load some distance from the wall. The deflection will be highest at the free end, but the stresses will be highest at the fixed (non-deflected) end. Strain (relative change in deflection per unit length) is strongly related to stress. If everything in some small area is deflecting by mostly the same amount, the area will experience small strain and thus small stress, but can show a dramatic deflection. Deflection diagrams can also misleading unless the boundary constraints are based in some real-life scenario. In the case of a real cantilever beam projecting out of a wall, we know the deflections are relative to an actual, physically fixed end of the beam. So we can intuit something about the deflection and possible strains and stress throughout the beam. But what about a violin sitting on a table top. Is there any point actually physically constrained relative to the deflection of the rest of the violin? Turn it on it side. The deflected shape of the violin does not change. We say the violin is an "unconstrained body" and we must arbitrarily selected a point where all degrees of freedom are specified as zero to stop the numerical solution from blowing up. One would normally illustrate that point on a deflection drawing so one could judge relative deflection among the various parts of the object. As a final point in what has surely turned into an excessively long-winded rant on the science of solid mechanics, notice that the areas of high deflection on the violin diagram are all about the same color. That means the material in those areas have all deflected about the same amount, which means they are most likely under low strain which implies low stress. This is assuming the deflections are taken along the same direction.
  4. I am familiar with Colin's work on mode shapes, but I don't recall any analysis of plate stresses. You would need to provide a reference for me to look at. The term "most of the overtone output" needs further clarification. The shapes of many modes may show significant deflection in the same general area. If this area is relatively thin and far from strong support areas, like the garland, sound post and bass bar, it would not be surprising to see high stresses.
  5. I set the clearance of the bottom of the E and G strings to the fingerboard, then use a 42mm radius template to set the heights of the D and A strings. Occasionally, I might encounter the odd E or G string whose stiffness is significantly different from the other strings. Using a finger position that is in-tune for the other strings may be noticeably out-of-tune on that string. I may adjust the height slightly to keep the finger positions "consistent" across all the strings. I use the third finger in first position as a reference.
  6. There have been FEM studies that start with the geometry of an actual violin box and measured material properties, and then give a very reasonable prediction of the measured acoustic properties of that box, such as response spectra frequencies and relative strengths. All of this can be performed on current personal PCs with existing software. The problem of using FEM/CAD is twofold: First, as Don mentions, there is no accepted standard on what quantitative acoustic properties represent a good violin. With no end point in sight, there is nothing to design to. Second, assuming one could measure all the relevant properties of a world famous Strad and your FEM/CAD software precisely predicts the violin's acoustic properties, where are you going to find wood to exactly match what is in the Strad? The problem, given any old piece of spruce tell me how to carve it into a fabulous sounding violin, may also suffer from "You may not like what it looks like no mater how good it plays." syndrome.
  7. Thanks for the post. It was especially generous of you to make the research free for public viewing. I was wondering why a paper filled with meticulous scientific measurements would start with multiple controversial claims like, "Despite tremendous advances in sciences and arts since the industrial revolution, violin making represents a singular case that has undergone a functional decline." I won't rehash the controversies surrounding the old vs. new debate. A search will reveal copious discussions on this topic. Starting a serious scientific report with such heatedly disputed claims would suggest a confirmation bias that does not seem to have any real connection to the actual investigation. You found obvious differences among the wood in SOME old instruments and new wood. There was even variation among the old instruments. Maybe a few of the differences were due to natural aging. Maybe a few were due to intended or unintended wood treatments. How any of this is related to things like quality of tone, projection and playability was never made, even in a cursory fashion. Did you really need to make those statements in the introduction?
  8. What Davide and MikeC said. Make sure it is dewaxed shellac. A simple and effective ground/sealer that will accept both oil and spirit varnish finishes. If you are asking for a ground before applying a shellac finish, use the thinned shellac mentioned above, or do a search on PoP (Plaster of Paris) or Gypsum grounds.
  9. Loss of transparency is due to the production of materials that reflect light before it reaches the wood surface. Good quality, dewaxed shellac and alcohol soluble resins do not have such chemical reactions due to aging. One can find spectacular French polished furniture in museums that maintain their clarity of finish a great many years after they were initially polished. One can also find pieces with oil varnishes that had unstable pigments added that aged into a dark, opaque paint over the years. We humans have a proclivity for inductive reasoning: reaching broad generalizations based on a few observations. I have fallen victim to this more times than I care to admit.
  10. From what I read, he basically says Ground = color + seal, Varnish = color + protection. No argument there. The materials he uses are things that have been discussed many times on the forum. The "tonal" effects on the violin especially in regards to the use of shellac? Need more info.
  11. Sure. But there is insufficient information for someone else to repeat (or test) the results. Waxed or dewaxed shellac? Multiple coats or one thin coat? Applied as a viscous ground or highly diluted before use? Any number of these factors can account for meaningful changes in the overall properties of the finished plate.
  12. One can buy "dye" that is soluble in alcohol or water. It gives a transparent color, meaning you can see right through the liquid. This is in contrast to "pigments", also known as paint, which colors the liquid by blocking the light.
  13. I experimented with turmeric in shellac finishes, but it was not color fast. It looked great for a few months then eventually faded. There is supposed to be a way to "fix" the color the stop the fading but I never discovered the secret. I added some transparent dye to give a reddish/orange tint, but once the yellow faded the overall finish lost that nice "brilliance" that your violin has and took on a more brownish appearance. Keep an eye on it. Maybe your mix of ingredients will will keep the yellow color fast.
  14. I am always willing to concede that someone making anecdotal claims about what they observed, actually observed something. But I reserve the right to maintain my skepticism when they offer an explanation about why they observed it. Krutz's comparison of a violin top to a mattress spring is one of those explanations. Other than the bridge feet, just what is loading the top normal to the surface? Most of the loads in the plate due to static loads and vibrations are taken up by shear, tangent and bending stress thru the thickness. If a coating is causing interference with these deformations, the coating must be relatively thick, or has soaked into the wood by a considerable degree. Spirit varnishes that are not dewaxed can be very soft. Dewaxed shellacs can be hard and very wear resistant, which is why some people use very thin coats as a protective "polish".
  15. Nice. What type of ground and varnish do you use?
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