Dennis J

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About Dennis J

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    Adelaide, South Australia
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    Anything and everything.

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  1. Maybe you are right. Given the top centre of the arch, a low point or line for the recurve, the end of the arching figure at the edge crest, and most importantly the inflection point, it is possible to draw freehand an arch profile. Of course the inflection point has to be in a realistic position. I've done it numerous times. If you check your drawn line against french curves, one for the upper convex part and one for the concave lower part, you will realise just how accurately it can be done.
  2. It seems to me to be at odds with the idea of an arch. I think it results from working methods commonly used to shape violin plates and has come to be the norm. If there is not a clear transition between the upper arching and the scoop at the inflection point a flat area results. Very difficult to avoid and I don't think it enhances the arching visually.
  3. I don't know why you would want any straightening in that area. I see that as something to be avoided, as I have just posted. It tends to result in a narrower upper arch. But it shows how a little difference in the arching profile can result in a fairly significant difference in the arching shape. I would point out that any pronounced narrowing of the upper arching at the bridge position might compromise how well the bridge feet fit.
  4. I wouldn't speculate about possible tonal outcomes in relation to arching because I simply don't know. For all I know arching has no bearing. But I strongly suspect it does because it can vary in height and shape so much. One think I think important is that everything above the inflection line is convex and everything below is concave. No flat areas. Particularly at the upper and lower bouts. The widest arch at the lower bout fits that criteria. It is a very shallow convex curve. I use french curves to mark the upper and lower parts of the arching when marking out the aluminium template blanks. And filing them to shape after sawing close to the line requires a lot of care, but is not difficult. However, I know that replicating that very subtle compound curve when shaping a plate just using shadows would result in something much less precise.
  5. Well that is interesting. That's the one at the bridge position and the same width. But how do the other arching positions compare? Keep in mind the system I've produced is meant to produce a coordinated set of guides. What do you mean by the read lines?
  6. I thought I had just about exhausted my contributions of wisdom or lack of to this forum. However, I have thought of an aspect of the subject which might put things into perspective or clarify them a little. I've measured the height of the convex part of the arching profiles on the layout I've shown here. That is from a line drawn between the top centre of the arch and the inflection point. It averages roughly 1.8 mm or from about 1.6 mm to 2.0 mm. That is not much, so reducing the height of those curves by say just .5 mm will physically and visually flatten that curve considerably. And increasing the height would do the same the other way of course. I think makers are mindful of the need to keep good convexity in the area of the inflection point and a little above, but it is very difficult to avoid cutting in too far. So, without arching guides, I think some flattening is almost inevitable in the course of shaping. And I think that explains the occurrence of that sort of characteristic, both on some early instruments and at a guess most present day ones. That leads me to think it is probably next to impossible to replicate the arching profiles in my layout without using the associated templates. And that is why I tend to think some early makers used very specific arching guides like the ones I have shown.
  7. I disagree with most of what you are saying. I'm not sure I'm enjoying it and I probably should be doing something else. I'm sure the Cremonese had the mathematical ability to construct french curves for any purpose and there's no doubt they did. However, in my previous post I explained how I use or orient french curves because it's obviously important. Your examples of arching resemble curves oriented in a way opposite to what I do. I believe my arching matches early makers' arching more closely than yours. That is with the part of the curve with the longest radius of curvature at the top centre of the arch.
  8. Something that I'd like to point out is that when using french curves to draw an arch I place them at the top centre of the intended arch with the part of the curve with the longer radius at that point, and the part with the shorter length of radius at the inflection point. This means that when the other side of the arch is completed there is a smooth connection between the two. With no peaking. And in the scoop the part of the french curve with the shortest radius is next to the edge of the plate.
  9. No. The arc in the layout serves two purposes. As a flat arc at a nominal (4.5 mm) edge height on the horizontal axis determining the inflection points' distances from the edge of the plate. And, tilted at 6 degrees (for the top arching) determining the height above the nominal edge height at each cross-arch position of each inflection point. So the waist cross-arch position (at the narrowest part of the Cs) has the highest inflection point. And at each end of the arcs, at the uppermost and lowest cross-arch positions the elevation is zero, or at plate edge height. The fact is that the inflection point for both the upper and lower bout and right around the top and bottom of the plate the inflection point is at edge height, or at the beginning of the scoop.
  10. As far as I can tell early Cremonese makers made violins based on original patterns and geometry, and that their work was very precise. That's not to say they didn't vary what they did. The geometry they used was proportional and flexible, just like the arching plan I've presented here. The outline pattern shown here, which I drew up, is close to one of Andrea Amati's violins, not Nicolo's.
  11. You are getting close to saying they made violins like cheap ones made in China today. There is no doubt those workers are highly skilled. Or, for that matter, cottage industry ones made in Europe during the 1800s.
  12. No, I didn't say the final scraping. I said the final stages of their arching. Big difference. It's all about controlling the shape. That is what the arching templates I've shown are for. I'm not sure that people over analyse anything these days. They just soak up what is fed to them.
  13. This is a circular argument but I'll try anyway. Let us assume for a moment that early makers knew how to make arching templates the same way I have outlined and were as skilled as you say. Why would they then not use those templates to check their arching in its final stages. Those templates, being as accurate as they are, could have been used with scrapers to refine the arching even after the plates were glued to the ribs. That would have resulted in what we now see of their work. That approach is the opposite to what contemporary makers seem to do now. Generic or copied templates are used to do most of the work and the maker then refines the shape by eye.
  14. I don't think about tolerances. I just use digital calipers to take arc measurements from the plan to calculate the height of the inflection point at each arch position. Even then I treat that height mark as a guide. I probably get close to .2 mm accuracy. And by using dividers I can transfer the horizontal position of the inflection points from the plan to the aluminium blanks accurately. So, even with inevitable inaccuracies in the drawn plan I don't think accuracy is much of an issue. Although the arching templates I have made are very accurate I think the biggest benefit is that they can be relied on to work together because the height of each inflection point is located along an arc as it should be. That is an absolutely necessary requirement. And that particular aspect of arching is definitely in evidence in early makers' work. So, in my opinion, very high levels of accuracy are achievable with the right methodology.
  15. Probably not a good way to describe it. I'm alluding to french curves which are spiral forms, just like scroll geometry. I'm no expert on the subject but early makers would have been familiar with it. They knew how to draw accurate ellipses as well. It has occurred to me that they could have used various ellipses to draw the upper convex section of the wider arching, as could anyone with a CAD program.