Belly cross arch

Now I'll explain how I design the cross arching. Most makers use the 5 cross arch profiles, make templates and carve to suit. That's fine for those 5 places, but what about the rest of the violin? At risk of being called a heretic I'll admit I work the inside of the arch first. After defining the long arch I make scans of the cross arches, mark off the thicknesses and tape them on the light box. Using my chain as before I find how wide the original catenary cross arch was. On some instruments the catenary is almost the whole of the inside arch. Others have a lot of recurve, and the catenary curve may be a long ways in from the rib linings. Generally I've seen that in the C bout the curve ends up close to the linings. The upper and lower bouts vary with the model. By finding the widths of the catenary arch at these 5 points I can draw up a curve that blends them together. The outside of the cross arch is a cycloid, or a variant of one. If the maker had the right combination of arch height and width on the inside, the resulting arch on the outside will be perfect. Stretching the arch wider on the inside gives a fuller arch with less recurve. You can guess that a narrow cross arch makes an outside arch with a lot of recurve. Different long arch heights and shapes will work differently with different inside arch widths. It's all part of the design. If you find the right structure, on the inside, for the model you are trying to make, I'm sure the results will be better. The drawing shown here doesn't have the edgework, but shows the catenary on the inside and the cycloid on the outside. The thickness is 3mm at the low point of the arch and 2.5-2.7mm everywhere else. The area from where the liner is to where the catenary arch ends will be blended in while thinning and tuning the belly as a way of controlling the stiffness.