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<DIV><FONT face=Arial size=2>good evening to all,</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>I have been reading the comments on =
shear force
with much interest.This being the first time I have felt I can =
offer some
thought on a subject I hope that it helps.Basically it follows what most =
other
people have been saying.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>1.Stress is the force per unit =
area on a body.
e.g. the force applied to a material 25m^2 is 100N, the material is =
under a
stress of 100N/25m^2=4Nm^2</FONT></DIV>
<DIV><FONT face=Arial size=2>2.Shearing forces try to slide =
particles or layers
of a body over one another. </FONT></DIV>
<DIV><FONT face=Arial size=2>The string exerts a force of 12kg<FONT =
size=1>+/-
5kg </FONT><FONT size=2>on the bridge pin which is trying to =
shear the
bridge pin in two.As the bridge pin has a high resistance to shearing =
forces the
pin exerts a compressive (relatively speaking) force onto the bridge =
this is
resisted by the material around the pin.As the wood is able to resist a =
shearing
force is felt at the glue joint between the bridge and soundboard =
(assuming
there is no bridge cap) as this is extremely strong it resists the =
initial
string force.I am sure you have all seen what happens when the glue =
joint fails
between the bridge and sound board, usually the bridge has moved
position(depending on other variables)I feel t</FONT></FONT><FONT =
face=Arial
size=2><FONT size=2>he tensile force between the bridge pin and =
CA glue is
negligible.Imagine if there was only the tensile strength of the glue =
holding
the bridge pin and not the wood , there would be no way the tensile =
strength of
the CA glue could resist a stress of 120N acting on an area
.775mm^2.</FONT></FONT></DIV>
<DIV><FONT face=Arial size=2>Also because the glue joint between the =
bridge and
soundboard is so strong (for the forces we are using) </FONT><FONT =
face=Arial
size=2>we could assume that the bridge and soundboard are one. =
So now it
could be said that the bridge pin is exerting a shearing force on the
bridge/soundboard.When bridges split it because this is the weakest link =
in the
chain, I seriously doubt a bridge pin will ever shear and as long as the =
glue
joint is strong the bridge will never shear from the soundboard. The =
wood around
the bridge pin will give usually give way when the holes are =
usually
drilled to close together and/or the hole is drilled to close to the =
edge of the
bridge.</FONT></DIV>
<DIV><FONT face=Arial size=2>I am doubtful as to how much =
strength the CA
glue actually offers to the resistance of string forces(long term) I =
would think
reducing the string force on the bridge pin would be a better move of
recap/replace the bridge. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I hope this has helped, apologies for =
writing some
much.</FONT></DIV>
<DIV><FONT face=Arial size=2>time for sleep, good =
night/morning</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Stuart Balsillie</FONT></DIV>
<DIV><FONT face=Arial size=2>Piano Technician</FONT></DIV>
<DIV><FONT face=Arial size=2>Victoria</FONT></DIV>
<DIV><FONT face=Arial size=2>Australia</FONT></DIV>
<DIV><FONT face=Arial size=2><A
href="mailto:sabalsillie.@bigpond.com">sabalsillie.@bigpond.com</A></FO=
NT></DIV>
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