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Occasionally I am asked to elaborate on the specifications refering to crown standards and tooling using crown over six feet. Here is a very rough attempt. The 7/16 would be the height at the middle along a 72" board if it were to be bent upward, measuring from the middle of the straight position up to the top of the curve. A 60" jig or crown standard, is just a cutoff version of the same board shown. When you hear referance to a 50 or 60 foot radius, this would actually produce a crown that is .900 at the mid point. If a rib were cut to such a high arc, it would produce much too much crown in a soundboard. What I understand is refered to with this radius, is the arc to be introduced into the soundboard using STRAIGHT, or UNCROWNED ribs ! This would then allow the soundboard and rib to flex back again somewhat, after the glue sets. This would end up with a radius somewhere in the middle of the original inch height. I dont see how you can have much control over the crown once the forces that be take over. it also seems that a straight rib will forever try to deflate the crown in the board, and even more so with all of the forces of downbearing on it. I only have experience with crowned ribs, and boards with much less stress introduced into them. This theory, is most likely understood better by more experienced piano people than myself. I hope this has been a help. |