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Arching of the front and back
For arching the plates, the best guidance I’ve found is in Sacconi’s book on Stradivarius’ violins called “The Secrets of Stradivari”, where he gives the ideal ‘contours’ of front and back plates, and tells us just where to put the highest point of the plate.
I like the method that Juliet Barker teaches at CVM in Cambridge that can also be found in her book. Instead of using the long and cross ‘arching templates’ that so many books get you to cut out and use as a guide, while the inside of each plate is (perfectly) flat use a pencil gauge to create the arching contours of your choice. This ties up well with Sacconi’s ‘contours’ in his book mentioned above.
Last summer I had cut elaborate cardboard contour guides like David Langsather’s and Sacconi’s for use with the pencil gauge at the CVM workshop, but the reality is that a tutor comes along a says “You don’t want to do it like that!”. So all the painstaking work was for nothing: it’s about a feel and look for that arching, and in retrospect, I think they are right - the contour guides are just guides.
There’s also guidance in any of the various books on violin making in the ‘Really Useful Links’ page.
The front and back should have different arches. The front or belly has a longer, flatter long arch and cross arching than the back. Bruce Ossman in his book on your first violin (see here) has them the same for simplicity, but there is no need to do so.
Here’s how Onnes Violins sets the arching on the back of a ’cello he’s making using various workshop tools, including power tools!. The same technique could be applied to a violin or viola. He also has an interesting page on thicknessing and tuning the plates of a ‘cello here using a laptop and Apple’s ‘Perfect Pitch’ program.
Darren Molnar has some interesting things to say about arching on his site, particularly about using Curtate Cycloids .
The Strad Magazine has a scanned copy of Quentin Playfair’s article on cycloids from The Strad, 1999: you can download: Part 1, and Part 2. I met Quentin again when he taught at Cambridge (CVM, UK), and here’s a picture of him (centre) in the workshop. A skilled craftsman who knows a lot, and can tell it with tact. These cycloid shapes are much easier to create than to describe - especially in maths, as they use parametric equations. But it’s quite easy to create an arching profile using a spreadsheet, and then use the pencil gauge shown on the Tools page.
T hicknesses of the front and back
The New York Times printed an article in 1994 called “Perfect Violin - Does Artistry Or Physics Hold Secret?” which is available on Peter Zaret’s website here as a .pdf file. He has an interesting modification to the standard bassbar and other good stuff on violins. Anyway, the original article is difficult to read as the text is small, so I have reproduced Carleen M Hutchinson’s thickness plans from it (see and click left) for a Mezzo violin (an oversize standard violin!), but the thicknesses are all but identical to Sacconi’s plate thicknesses for a normal violin. The text of the article is here. Right click it and use “Save target as ...” to save as a .jpg file. These plate thicknesses are a very, very good starting point.
The thickness of front and back plates for great Guarneri ‘del Gesu’ violins can be found here, reprinted from ‘The Strad’ Sept. 2005. Borman Violins also shows some fascinating animations of violin and other plates here.
There are also plans (A3 size) available for the Ole Bull Violin Project than can be found on the Landon Violins web site, plans for the Ole Bull Guarnerius of 1744. These include the shape, the arching and the plate thicknesses.
Erik Jansson also gives guidance on thicknesses in his articles “Acoustics for Violin Makers”, Chapter 5, Fig. 5.21, page 24.
I have  derived a Fig. 1 below to show where to thin a front plate (the belly) to reduce either Mode 2, Mode 5 or both frequencies. Click on it to see the Figure in more detail. Right click it and use “Save target as ...” to save as a .jpg file.
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