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Dennis J

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    Adelaide, South Australia
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    Anything and everything.

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  1. If you take into account the angle of the bevel there is not a great deal of radius there. Sharpening with a side to side or slightly oblique action will cut the corners back to some degree. If a gouge is badly out of shape I square off the edge by holding the gouge vertically and drawing it back towards me on a diamond plate making sure to tilt it so that the edge is square to the angle of the bevel. The further you tilt it the more you will cut back the corners.
  2. I'm not trying to convince anyone, I think it speaks for itself. There is nothing theoretical about it. What excites me about it is that I can design any sort of arching I want especially regarding the ratio of convex and concave components. That is the main determining factor on the overall arching shape. I can draw up a fairly accurate set of templates for the back and front in about four or five hours starting with the long arch templates I've decided on. Totally predictable and repeatable.
  3. Making templates like I have posted is time consuming. But I think that the concept behind it is important. I think exploring design possibilities on paper, especially regarding arching, is something new makers could benefit from.
  4. I'm only interested in concrete working methods which might lead to better outcomes. I'm too skeptical to believe that makers who listen to what the wood is telling them have any idea of what they are talking about.
  5. The Cremona makers lived post the Medieval period. And they undoubtedly had all of the skills and mathematical knowledge necessary to carry out their trades. There are complexities in what I have posted, mainly around edge height, but the underlying concept is quite simple. The inflection point location is calculated by a simple right-angle triangle calculation as defined by its position along the arc. Having arrived at a basic workable radius and orientation of the arc by trial and error (which can be varied depending on what sort of outcome you want) I have no trouble drawing cross-arch templates specified by that geometry.
  6. I think what I have posted about arching fits in the category of violin geometry just like the 4-circle method used to design a pattern shape. There is clearly an underlying geometry to arching however you go about carving plates. And that is that all inflection points lie on a straight line, looking from a 3 dimensional point of view. Deviating from that won't help the aesthetic or functionality of overall arching. The long arches are purely functional. The back of many early instruments seem to have their own peculiarities, particularly approaching the button. I'm sure the subtleties there aren't noticed by many.
  7. If you are prepared to spend the time you might be able to make your own. Cross-arch profiles just about make themselves once you have measurements for heights and inflection point positions. Of course the heights are determined by the long arches' shapes. Once you have that, figures can be set for the cross arches. Working out the general geometry that early makers used for that requires a bit of research and guesswork. The pic shows what is my latest version.
  8. Of course toothed blades track to some extent. But having unevenly spaced teeth won't change that. All that you can do is plane in slightly different directions. I've just used a Veritas block plane fitted with one to plane rough sawn ribs and there will always be high sections left preventing further progress. The solution is to follow up with a plane fitted with a plain blade. In the case of ribs both blades should be sharpened at a cutting angle of at least 50 deg. to prevent tearout.
  9. Well some makers do a very good job replicating examples of past makers' work. And as you say the way tools are used will play a large part in the results. Arching guides can predetermine an arching outcome. Mainly how full or otherwise it is once an inflection point is determined. And they simplify the whole process. Arching does have a definable geometry and I'm absolutely sure early makers knew of it and how to use it. Makers are always asking questions about arching and how important it is because they see very few practical, predictable ways to approach it.
  10. The only thing necessary to construct an arching profile is to locate the position of the inflection point between the upper convex and lower concave curves at any cross-arch location along an arc. And an arc drawn between the widest part of the upper and lower bouts can be used to calculate both its height vertically above the level of the edge and its distance from the edge horizontally. The inflection point is at edge level at both the upper and lower end of the arc, all of the recurve section of the arching is below edge level. So the three-dimensional position of the inflection point can be ascertained from an arc drawn on a sheet of paper. That arc can be drawn from a vertical between points where a double-string-length line crosses the uppermost and lowest cross-arch lines. How ISO lines can be used to draw arching profiles is beyond my understanding. As far as I can see they are a misleading irrelevance as far as trying to draw or make arching guides is concerned. Only geometry that can be used to make arching templates or patterns is of any use.
  11. Dennis J

    ......

    I would advise anyone planning to make violins that they study the geometry first. Soundhole placement is covered by that.
  12. Dennis J

    .......

    I've tried making inside moulds with basic measurements. And while the results are ok important things like the disposition of and the distance between corners can be a bit problematic. The 4-circles method works on proportionality so everything is balanced and practical whatever the starting measurements, such as the width of the lower bout, are.
  13. Dennis J

    .......

    Knowing the geometry of the violin is the only way you can resolve design issues if you want to make your own form/mould. And the 4-circles method described by Kevin Kelly is the best way to go. I have posted arching design methods, the last one is currently on page 57 of the Pegbox. It covers how to make long arches for both the front and back plates which can be used to establish heights for each cross arch as well as how to construct each cross arch profile.
  14. Volcanic pumice deposits are common around the Mediterranean and it is a commonly used sanding grit. I use it loose on a flat granite slab concentrating on the larger end blocks first and then the corner blocks. And I test for overall flatness on the saw table surface. It is a fairly slow process but I find it the only reliable way to get the blocks, lining and rib surfaces flat. In my experience sanding sheets glued to a flat surface always wear the rib/lining surfaces below the level of the block ends. And it is not too hard to imagine why that occurs. I should add that I do that with the inside form still attached.
  15. Of course it does. But I wouldn't think clamping pressure would be particularly significant as far as plates are concerned. I don't think there would be any significant residual stresses left after clamping because the gap being closed is so small. And, as I've said, I don't think clamping would close such a gap anyway. But, as far as stresses are concerned, I think things like installing purfling after the plates are glued to the ribs might be something worth exploring.
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