Violin Forum/Message Board

[Joseph Leahy]

I'm trying to get a good handle on arching principles and have a couple of questions. Here is what my understanding is so far.

The back.
The longitudinal arch is composed of a large circle or catenary curve (pretty much the same at this radius) extending out towards both ends. The ends are then gracefully tied into the overall design of the violin with minimal recurve as more recurve will possibly diminish the longitudinal strength of the back. The high point is the central point of the instrument. The cross arches are based on cycloids.

The top
The top arch is composed of a central flatter section based on a very flat circle or catenary connecting at each end to more rounded areas based on a circle with a smaller radius and then similarly tied into the ends of the instrument. The high point is again in the centre. The cross arches are based on cycloids. The channel generally moves closer to the purfling or at least narrows as the arching increases.

When strings are added and tightened, the tension on the back tries to lengthen and diminish the height of the back. This is somewhat offset by the soundpost. Due to these forces, the high point of the back may tend to shift towards the soundpost area.
At this time, also, the top is in compression. Although, there is a downward force on the bridge opposed by the soundpost, the top still tends to narrow and rise across the c bouts due to these longitudinal compressions.

Hopefully, I'm somewhat on track so far. I have three questions that will help me understand things better.

1) Is it always the case that the top will move up after tightening the strings on a new build or does it move less with a better, stronger long arch design? If the top does always move upwards, should the top always be carved 1 mm to 1.5 mm lower than the desired final height to compensate and ensure the fingerboard does not end up too close to the body requiring a neck reset or bridge adjustment? If these forces do always change the height, then starting at 16mm would give a 17mm to 17.5mm final height which seems high to me. In this case, one should start at say 14.5 mm if the desired end height is 16 mm.

2) Specifically related to the Titian. The strad poster drawings show the current height of the back at 14.5mm and the top at 15.5mm.
The back measurement seems a bit low so perhaps it has lowered somewhat due to tension...or maybe it was originally designed at 14.5mm.
If the top has moved, say 1 mm to 1.5 mm, this would mean that the violin's original carved top height was 14.5 mm to 14 mm which seems pretty low as a starting point to me.

3) I have seen new makers say that after stringing up the violin, they find the fingerboard is then too close to the top. I am surmising in these cases that the top has risen. Does the central flat part rise in conjunction with the more rounded parts in the top or are these more rounded areas bulging somewhat from the forces, leaving the central section still flat but higher?

Lots of detail here. I would appreciate comments. Thanks.

Joe

[ctviolin]