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<DIV><FONT face=Arial>I'm so excited, I just can't hide it, awaiting the test
results.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Al Guecia</FONT></DIV>
<DIV> </DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=JD@Pianomaker.co.uk href="mailto:JD@Pianomaker.co.uk">John
Delacour</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=pianotech@ptg.org
href="mailto:pianotech@ptg.org">Pianotech List</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, April 21, 2008 7:03
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: stretching wire</DIV>
<DIV><BR></DIV>
<DIV>At 20:29 -0500 20/4/08, you wrote:</DIV>
<DIV><BR></DIV>
<BLOCKQUOTE cite="" type="cite">Well I have to admit this is very
compelling.</BLOCKQUOTE>
<BLOCKQUOTE cite="" type="cite">I am tentatively sliding off the agnostic
fence to join you.</BLOCKQUOTE>
<DIV><BR></DIV>
<DIV>Welcome!</DIV>
<DIV><BR></DIV>
<DIV>Although I have massive 10ft I-beams with 30mm web supporting my upper
floor, which I was planning to use for a vertical test, I have decided today
to do the test horizontally on the bass string making machine. The
apparatus is as shown below. The wire is given a normal English eye,
hooked onto the machine and tensioned with a determined weight. Near the
eye end it passes through a clamp at the end of a square steel tube that lies
free on the bed of the machine. Any movement owing to the eye tightening
up will therefore move the tube bodily and not affect the results. At
the far end of the tube a ball (eg. split shot) is clamped to the wire and
makes contact with a lightly-sprung pointer, behind which is a dial. The
tension is applied to the wire and the tube is adjusted on the bed of the
machine so that the pointer is upright and pointing to zero on the dial.
The wire is then clamped at the hook end. This operation must be done as
quickly as possible after the load is applied.</DIV>
<DIV><BR></DIV>
<DIV>This apparatus keeps the wire under a constant tension by means of the
dead weight at the left end of the machine. Though slight movements in
temperature are hardly significant in any case, the apparatus compensates for
any change by the fact that the steel tube will expand as well as the
wire. Any movement at the eye is isolated by the design from the test
length. Since only light clamping is required to secure the wire to the
compensating tube, there is no distortion of the wire at either extremity of
the test length. Any movement of the pointer over a period of time can
thus be attributed exclusively to an elongation of the test length.</DIV>
<DIV><BR></DIV>
<DIV>Does anyone see any fault in principle with the apparatus?</DIV>
<DIV><BR></DIV>
<DIV><BR></DIV>
<DIV><IMG src="cid:p06240803c432af03c9e7@[10.0.0.1].1.0"></DIV>
<DIV>___________________________________________</DIV>
<DIV>From Oscar Faber's Reinforced Concrete
<http://books.google.co.uk/books?hl=en&id=_8JJewhwDnQC&dq></DIV>
<DIV><BR></DIV>
<DIV><BR></DIV>
<DIV>STEEL STRESSES</DIV>
<DIV><BR></DIV>
<DIV>Steel stresses are limited to provide a margin of safety on the steel,
and also to avoid excessive stress-relaxation due to creep of the steel.
In this way, the risk of permanent deformation from overload is also
reduced.</DIV>
<DIV><BR></DIV>
<DIV>For hard-drawn steel wire, C.P. 115 (1959) recommends the initial tensile
stress should not exceed 70 per cent of the ultimate strength, or the 0.2 per
cent proof stress, whichever is the less. To reduce loss of prestress
due to creep of as-drawn wires, a 10 percent overstress is sometimes held for
two minutes.</DIV>
<DIV><BR></DIV>
<DIV>For alloy-steel bars the initial tensile stress should not exceed 70 per
cent of the ultimate strength, nor 85 per cent of the 0.2 per cent proof
stress, whichever is the less.</DIV>
<DIV>___________________________________________</DIV>
<DIV><BR></DIV>
<DIV>JD</DIV>
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