David- Looking at the 1990 edition of _The Calculating Technician_, I find the Tmax formula as you quote it on p. 11 and p.63, Table 9.2 As I understand it, the Tmax formula calculates 60% of the breaking tension Tb. (See p. 66.) His formula is Tb=Tmax/0.60 The example you refer to is on p. 7 and p.11. The tension calculated is 474 lbs. This is very high, and he says it is one of the highest he has ever seen. But if Tmax is 556 (55.7%% of Tb 999lbs.), then 474 is only 47.5% of Tb. By the way, I believe the 63 mils core wire in question would be a 29 gauge wire, unless the gauge calculations change at that diameter. Anyway, it's a big fat wire! Ed Sutton -----Original Message----- >From: David Love <davidlovepianos at comcast.net> >Sent: Apr 8, 2006 3:58 PM >To: 'Pianotech List' <pianotech at ptg.org> >Subject: Breaking point formula > >I'm looking at Roberts' formula for breaking point and he gives the maximum >as t(max) = .557d^1.667 > >He then gives an example of a string at whose tension is 447 lbs and whose >calculated T(max comes in at 556 lbs. He then says that this falls within >the prescribed maximum of 60% of T(max). Seems to me that 447 is 85% of >556. Is the formula he gives incorrect? > >David Love >davidlovepianos at comcast.net > > >
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