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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. Instead of using the ‘arches’ that so many books get you to cut out and use as a guide, while the back 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.
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 arch 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.
Darren Molnar has some interesting things to say about arching on his site, particularly about using Curtate Cycloids . These 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.
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