ctanzio

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About ctanzio

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  1. Vacuum also lowers the boiling point of water, so it is possible to get wood down to almost 0% MC with a vacuum chamber at room temperature. One of the challenges with thermal aging many materials is getting a high enough temperature to get results in a reasonable amount of time, versus having the material decompose through high temperature processes that would not normally activate at room temperatures. For wood, once one approaches 140C, all sorts of nasty processes begin to kick in that would normally not activate at room temperature. And this is for wood being heated in a chamber filled with non-reactive gas, like nitrogen. This is referred to in the literature as pyrolysis testing. In the presence of oxygen, all bets are off that thermal aging at elevated temperatures will simulate natural aging at room temperature.
  2. There are two broad changes that wood undergoes as it is "aged". 1. It reaches a stable moisture content with the ambient air. Freshly cut woods tend to have a significant amount of "free water". The weight of the water can exceed the weight of the wood fibers for many species of wood. But if you cut new wood to just a little bigger than the size you want to work with, typically +15% larger in all dimensions to account for shrinkage, and let it air dry in a space with about the same temperature and relative humidity as your house, it will reach a stable moisture content in about 1 year per 1 inch of thickness. Basically, for wood rough dimensioned to sizes you would need to make a violin, there is no difference in stable moisture content between 1 year old wood and "old" wood. 2. It reaches desired physical properties. Properties that are frequently discussed on this forum, like density, elastic modulus and sound speed, will mostly stabilize after the wood reaches a stable moisture content. After that, changes in these properties tend to be relatively small over many years. This suggests that new wood, rough dimensioned for violins, and dried for a year at room conditions, will achieve the same basic physical properties as "old" wood. However, there is a research to indicate that sound damping will decrease significantly up to 100 years after it is cut. Some makers have taken to thermally aging their wood to accelerate this reduction of sound damping. Kiln drying wood is a tricky thing because there are other affects associated with exposing wood to higher than room temperatures, such as destructive oxidation of the cell walls.
  3. The structural features that make a bridge efficiently and securely transfer string energy to the violin can be achieved by a variety of bridge shapes. I have no idea if the pictured bridge is one of those shapes, but I would reject it based solely on its appearance.
  4. I enjoyed viewing the restoration photos. Spectacular repair of the top plate that was cleaved its entire length.
  5. The balance point of the top plate and its center of mass are slightly different concepts. As Bruce pointed out, it is possible to balance the plate on the point of a pencil. This is the balance point. The center of mass would have the same position in some flat plane, say, defined by the plate edges, but would be located some distance below the point of the pencil on which the plate was balanced. How far down along the pencil would be a function of the arching as well as how the plate was thinned. One can use Newton's Laws of Motion and some non-trivial mathematics to compute the location of the center of mass, but that is beyond the scope of this forum. Physically, an object that is pushed at its center of mass will travel without any rotation. If it is pushed at a point away from its center of mass, it will move as if was pushed at its center of mass, but with a rotation about the point. This is a useful concept for figuring out the interactions of many moving machine parts, movements of planets about each other and the sun, and just about anything that can be treated as basically an array of rigid bodies. Most of the movement of a violin plate, once it is attached to the body, is due to bending deformation. Rigid body motion probably contributes very little to violin response. For vibrational modes, there are concepts called modal participation factors and effective mass which basically measure how much of the plate participates in a vibrational mode. This participation is one of the reasons that design just by matching vibrational modes can be misleading, especially free plate tuning without a bass bar and sound post. One can work hard to match a vibrational mode frequency, but do so in such a way that only a small amount of the plate participates in the vibration. So the mode would contribute little to the violin tone and power.
  6. If by French Polish you mean shellac dissolved in some kind of alcohol, there are two fundamental properties you should consider before using it. 1. This stuff will stick to and seal in just about anything. As has been already mentioned, dirt and discoloration will become a "permanent" part of the finish after French Polishing, even if applied as a very thin layer. Make sure the surface is clean of dirt and rosin build up and has the color tone you want before applying shellac as a varnish or a polish. 2. Shellac is highly leveling. The means using a polish technique can rapidly smooth out texture, from microscopic roughness that is making a worn surface appear dull, to pronounced corrugation due to deliberately raised grain meant to give the wood surface a more natural finish. This leveling characteristic is why shines can be achieved that approach a mirror finish. That said, shellac that still has some wax content can be used in a very dilute form, and a barely damp polishing rag, to create a soft sheen yet uniformly smooth surface that can preserve most grain texture and not change the color of the underlying varnish. The effect is similar to a fine wax polish. It has the added advantages of being wear and water resistant, and dirt and rosin can be easily removed with a soft cloth. It is also trivial to repolish areas that are subject to high wear, like the treble side upper bout plate and ribs. Unwaxed shellac, again used sparingly, gives a highly polished sheen while preserving larger grain texture and the color of the underlying varnish. Over-polish, or use a strong shellac solution, and you can quickly turn a violin into a mirror.
  7. Something transcendent and entrancing about ancient music. I suspect accidental or deliberate consumption of ergot (St. Anthony's Fire) and Psilocybe mushrooms (Flesh of the Gods) contributed heavily to musical inspiration, like rock music I listened to in the 60's and 70's. I am happy to report that after 50 years, the spontaneous voices and visions have stopped, but I can still enjoy this music. Thanks for the post.
  8. I experimented with water-based poly-acrylics and they gave crystal clear finishes. Every detail of fine and complex grain came through. But as you noted, they are difficult to get smooth. The basic problem is the short drying time (about 2 hrs) which means a short working time and lack of ability to "level" as they dry. I could not develop any type of French Polish technique to get it flat. There were always witness lines in the final direction of the rub (or brush). Also, poly-acrylics require some light sanding to the initial surface since they stick primarily through mechanical bonding. This can be a no-no if dealing with a fine colored varnish finish that you want to polish up with the poly-acrylic. I did achieve some degree of success by putting on a few coats, then carefully and progressively sanding from 600 grit to 3000 grit, and finishing with a good quality auto-paint polish. Because poly-acrylics go on so thinly, one must be careful not to sand through the layer to the underlying wood or colored varnish. Also, it is extremely important to remove every last spec of sanding dust before applying another coat or else it dries with tiny holes that look like areas of missing varnish. Unless there is some special need for wear or chemical resistance, I found it a lot simpler to polish up an oil finish with a dilute solution of clear shellac rather than deal with all that sanding and careful cleaning. Shellac is remarkably durable and can be easily refreshed. Another option I explored that might be of interest to the OP is modern oil-based spar varnishes. They have a long work time and dry flat without any brush witness lines. They have excellent leveling characteristics, dry overnight and once thoroughly dry can be easily sanded or polished to get various degrees of gloss. Most also add UV aging protection. A down side is that they create quite a thick layer with each coat. I had some limited success with various diluting liquids, like mineral spirits. Perhaps a thickish layer is not an issue with the back of a guitar or lute? Also, they do add quite a bit of transparent amber color to the finish.
  9. Thank you for posting details of your methods. Interesting to see you leaving a section of the neck flat a bit wider so you can use studs to align the fingerboard, and then trimming the flat width to match the width of the board. I've experimented with various approaches to aligning the fingerboard but I have not settled on a method. Each has advantages and disadvantages. I got the impression you will remove the board then reattach it later. How do you realign it after the neck width has been trimmed.
  10. The laws of physics say otherwise. When the neck bends up, it applies a shear and bending load to the violin box at the neck root. The violin box must deform to develop counter shear and bending loads or else the neck will continue to bend upwards until it snaps off.
  11. I binge on his YT channel too. His videos are both uplifting to hear, and depressing in the vast chasm separating my skills from his. There are certain subtle things about his YT "studio" performances that only a player can appreciate I think. For example, they appear to be closely mic'd as you can hear his breathing, but there is a complete lack of spurious playing noises, like fingers hitting the board, small squeeks and minor articulation dings on string crossings, bow hissing on long slow decrescendo notes. In this video, I liked how he seemed to change the lighting (or maybe a post-production trick) to make his violin appear red. Anyways, I started working on my triangle career and made the mistake of searching youtube for suitable instruction and came across this... Another one of my promising careers in music, ruined....
  12. After watching this, I realize I am not worthy to play the violin. I am switching to triangle. Thanks a lot for posting this and ruining my dreams as a violin soloist.
  13. To be clear, it depends on the direction of the loading. Consider table with a thin, flat top. A weight placed at is center will cause the top to noticeably deform downward. Bend the flat top into an upward arch. That same weight will now cause less downward deformation of the top in the direction of the load. Now place one side of the flat table against a wall and give a push on the other side. It would greatly resist any deformation. But an arch top table would deform more in the direction of the push. I do not see a 2mm slope in the ribs doing anything to increase load resistance of the plates. It is just not enough of a geometrical change to the basic shape of the plates to offer much help. It would, however, introduce measurable stresses in the box, and I see two possible advantages of this: 1. Stressing the plate due to the taper would change the frequencies of the natural modes of vibration. Like tightening a drum head. 2. The bend along the taper would place the belly into tension along its length. After stringing up the violin, the tension would be relieved as the belly is bent back due to the string loads at the scroll box and tailpiece peg. Prestressing beams and plates in the opposite direction of an expected applied load is an old and well-practiced engineering trick to allow a thin geometry to handle a larger load without buckling. Or maybe an ancient maker screwed up a rib when trimming the linings and said, "Oh well, I will taper the rib on the other side the same amount and add a little extra glue because Don Giovanni wants his new violin and I do not have enough wood to cut new ribs." The Don was so happy with his exotic looking violin that soon all the other makers in the village were tapering their ribs.
  14. Spruce and maple expand and contract the most due to moisture change as one travels around the growth rings (tangential), about half as much across the rings (radial), and very little along the length of the tree (longitudinal). One can notice this as a log dries out. Cracks tend to form along the radial direction as the wood shrinkage on either side of the crack is due to the high rate of change in the tangential direction of the rings. The rate of change due to moisture is similar among most maples and spruces used in violin making, although some maples can shrink a little more in the tangential direction than spruces.