johnms

If you look very carefully at old instruments with flat-faced end blocks you will find that the block faces are never parallel to each other.  Like so much of Cemonese violin design the little things are often subtly different from what you think.  

In this case I can only assume this avoidance of parallel faces is intended to prevent standing waves being set-up.

I have read a lot of comments that indicate a mismatch between cross and longitudinal arch height is normal. From the drawings I have seen it appears that arch height is simply measured from the underside of the top plate at the location the arch height is required.

One factor that might be producing this lack of correlation in top arch height measurements is a failure to account for rib height variation. I have yet to see a comment about making this adjustment.

From what I what I have observed the bottom of a rib usually follows a straight line while the top edge is effectively a curve with its maximum height in the area of the C bout.

Simply measuring arch heights relative to the underside of the top plate means you are taking measurements off different datum points. No matter what object you are measuring you cannot compare height measurements unless the measurements are adjusted back to a common datum. You have to either set up a common datum measuring line or else adjust individual measurements back to a common datum.

For violins this means either increasing cross arch height measurement by the rise in height in the rib or deducting that measurement from the longitudinal arch. Without making this adjustment it is impossible for the measurements to match. Keep in mind that rib heights are often different on each side.

I hope this first time poster is not telling experts how to suck eggs.