Violin Forum/Message Board

[MWard]

I would like to create and use curtate cycloids for my me next fiddle. I am using a Stad poster that has arching guides. Using those to determine height and width, with a bit of modification to fit my outline, I plan to print them out and create arching guides from there.

My questions for those who have done this are:

1. I am assuming that the height of the arch is measured from the lowest point of the channel.

2. is the long arch also done with a cycloid? If so, is the highest point generally a few millimeters in front of the bridge?

3. how do I compensate for the distortion that has occurred over the years? I am guessing that the heights of the arching on the poster are not as high as they were originally due to 300 years of string pressure. would this be greater for the long arch? Or am I worrying about something that is of little consequence, because the cycloids will for the most part compensate for me?

Any other ideas or advice would be appreciated!
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[Michael Darnton]

You are generally right about the cross arches. When working from posters, I use the widths as measured from bottom to bottom, and the heights as derived from the long arch I decide to use, based on the original, but not holding directly to it (because of distortion).

On the back I use a circular long template, and the top is a more complex curve that I've figured out myself, something slightly flatter in the middle. In either case, the highest point is in the center of the length--maintain symmetry in the long direction as well as across.

You will have to alter the ends of the long template slightly to blend in a scoop and rise to the edge that's consistent with the appearance of the cross arches. I usually use a half template of the closest cross arch, swinging it around the bottom and top curve. A full cycloid long arch will be too low and scoopy around the ends.
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[MWard]

How do you determine how to modify the existing template of the 300 year old long arch?
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[Michael Darnton]

You try to figure out what the intent was. I believe the intent of the back was a circle for the long arch. That is obvious to me in many examples. The top distorts quite a bit, and then you have restorers' imposition of what they think was going on, so the top is more difficult. I'd say make a theory, run with it, and see what happens. I do NOT believe the top was originally a circle like the back, except in del Gesus dating from his latest period, where that intent still remains clearly visible.
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[MWard]

Great info. I can see what you mean about the top, but I just can't visualize a circle for the back. I have looked at the cycloid/laser diagram on your website; I was wondering if you have a diagram (not necessarily laser/cycloid) that could illustrate what you mean about the back being a circle.

This has little to do with what we are talking about, but my teacher (born in the early teens) used to say he thought the arching was based on the inside of Gothic cathedrals, where you could hear a whisper from the back of the church in the front. Never been to one myself, but fun to think about.
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[Michael Darnton]

Remember, I'm only talking about the major part of the lengthwise arch, which is forced to change at the ends by turning negative approaching the purfling, and then going back up to the edge. Just a simple circle.

On this violin (a Pressenda) there are just a couple of inconsistencies that prevent it from being a circle--a lump where the wilder curl is, beween the upper corners, and a slight depression below that. On the average--and that's all you can hope for, especially on a violin that's 170 years old, it's an excellent fit, given that I didn't draw a specific circle for that violin (mine has a bit longer radius than the violin's back). http://darntonviolins.com/images2/circular-back-arch.jpg
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[MWard]

The Strad poster I am using is a 1737 Peter Guarnari. In measuring out the arches, I found that the back arch is 19 mm high from the bottom of the plate (there is no top arch template given.) The highest cross template is only 15.5 or so. I am confused by this--- first, I thought that 19 seemed high, and second, why aren't the cross arches 19 mm? This threw me when I went to design my cycloids.

In redesigning the back long arch, should I trust that 19 is correct? Right now I have the high part of the cycloids matching the high points of the cross archings, which are quite short of the stated long arch height.

In your experience, what are the general heights I should look for / try for when I design a top and back arch? (I will need to create a long top arch for it from scratch using the cross arch heights.)

I believe that the rib heights in the poster are roughly 29 and 27, but mine will be 30 and 29, if that makes any difference.

And last, I really appreciate your help in this and all matters you comment on here. I think I have learned more meaningful, important details from reading your posts than from any other source.
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[Michael Darnton]

Over time and under tension, violins tend to bow over like an old man, whose hump measured relative to his elbows will be less than measured from his forehead and toes. Same with a violin. Depending on how side views are shot, you might even see this on a photo, using a straight edge along the back and top edges. A 2mm sag at the center is not unusual at all.

Probably the height across the c-bouts is a little low (backs tend to flatten over time), but real, and the height relative to the ends is a result of the sagging distortion of the body. In this case, I'd probably do something like 16mm or 16.5, and the same for the top.

Rib height plus both arching heights should be around 62mm or so for this period of instrument. Perhaps, for this maker, a bit higher, but not too much.


Thank you for the reinforcement.
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[MWard]

Thanks for all the help. Today I drew out the top and back arches, and tonight it's off to the cycloids.
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[actonern]

Michael:

When using cycloid generating software you can choose where the bottom of the curve will be. Looking at Cremonese violins it looks like the bottom of the curve is closer to the edge in the mid-bouts and further in on the upper and lower bouts.

How do you choose how far in to place this bottom? It makes a big difference in the overall look of the arch, as well as the look of the upward sweep towards the edge.

Best regards,

Ernie

[Michael Darnton]

Your observation is correct. I steal the numbers for scoop placement from real violins and posters. :-) I don't have a strategy for how they might have figured it out.
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