> I am interested to know where you got your list of breaking strains > which differs so greatly from mine and Paulello's. One from Mapes, and one from Roslau, neither of which you will find credible, as you have already indicated. For scaling work, I use Al Sanderson's generic formula of Tension/(2528*diameter(inches)^2), which corresponds reasonably well with the Roslau numbers. I keep core tensions under 55% by this formula. For your #21 core example, your 70% limit would be 283lbs by your tensile strength number, while my 55% by Sanderson's formula would be 307lbs. That would be 76% by your figures, while your 70% would be 51% by mine. Not that far apart. The point is to retain a reasonable safety factor, whatever the numbers used. There are a number of commercial scales, including Yamaha and NY Steinway, having core tensions well above 60%, and in cases above 70% by Sanderson's formula, and showing little to no tendency to self destruct. For what it's worth, Ron N
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