Someone wrote; <<Does this mean I have been wasting my money, by using 1/2" bolts?? >Does everyone else just use 1/4" bolts?>> A while back, look in the archives because I no longer have the information, I checked out the tensile strength of bolts just for the purpose on determining what size would be adequate in these repairs. 3/8" or 5/16" bolts are easier to work with, but 1/4" is more than enough for any piano. Consider this. - If I remember right, the tensile strength of steel is about 188,000 pounds per square inch. Calculate what part of a square ince a 1/4" bolt, minus threads, represents. Remember also, - a 1/4" wire cable breaks at about 4,800 pounds, and a piece of piano wire with a teeny tiny cross section, say #26 wire, holds several hundred pounds of tension adequately. I think it would be inadvisable to have a flat cast iron plate held against the block with a force of more than perhaps 50 to 100 pounds, because of the local deformation and chance of cracking at the bolt hole. Bill Simon Phoenix p.s. - early in my piano career, I put five 3/4" carriage bolts across the top of the plate of a big old upright during this type of repair. The rounded heads looked just the right size from the front of the plate. From the back, it looked like I was building a railroad bridge. Each 3/4 bolt would hold something more than twenty thousand pounds before breaking. I bought a bunch of these bolts for future repairs. Still have them. They are for sale if you want them! (:-)
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