Breaking point formula

[David Love]

You're right, I think I misread it.  So the breakpoint is actually d^1.667?
And the safe upper limit is 55.7% of that.  



David Love
davidlovepianos at comcast.net 

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of ed440 at mindspring.com
Sent: Saturday, April 08, 2006 5:16 PM
To: Pianotech List
Subject: Re: Breaking point formula

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 
>
>
>