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From: Gary Casey <casey.gary@yahoo.com>
Subject: Tungsten and other heavy metals
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There was some discussion on the use of tungsten as a balance weight, so I =
did some research on the density of various materials - here is a list of a=
pproximate specific gravities:=0ATypical epoxy resin - 1.5=0AAluminum - 2.6=
=0ASteel - 7.8=0ALead - 11.3=0Atungsten - 19.2=0A=0AIt would appear that th=
e higher density of tungsten would allow a more compact balance weight, all=
owing the weight to be more concentrated to the extremity of the available =
space, reducing the overall weight.  But things are not usually as simple a=
s they at first seem.  In order for lead to be effectively used it has to b=
e cast in a shape to fit the space, which is what I did.  It is hard to get=
 all the air bubbles out, but a lead casting can be reasonably dense.  The =
tungsten, however must be used in the form of powder or rods held together =
by an epoxy matrix.  I don't have directly-related experience, but I would =
guess that it would be very difficult to get a 90% by volume tungsten mixtu=
re in epoxy (resulting specific gravity =3D 17.4) and if one was a little t=
oo casual and wanted to get an easily pourable mixture he could end up with=
 a 50% mixture (specific gravity =3D 10.4), less dense than a lead casting.=
  With reasonable care, which means careful
 measuring of the epoxy and thoroughly mixing without trapping too much air=
 I would guess a 70% mix is reasonable and 80% is possible, but not likely.=
  In comparison, rods perfectly nested in a linear pattern, not hexagonal, =
will be 78% "packed."  A 70% mix will yield a specific gravity of 13.9, 23%=
 greater than lead.  Will that reduce the overall balancing weight by 23%? =
 No, because only part of that weight is at a small radius - the weight sav=
ings is more likely to be about 10% or less.  Is it worth the trouble?  It =
might be if an accurate lead casting is particularly difficult, but otherwi=
se I doubt it - at least that was the reasoning when I decided to use lead.=
=0A=0AGary Casey=0A=0A=0A      
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<html><head><style type=3D"text/css"><!-- DIV {margin:0px;} --></style></he=
ad><body><div style=3D"font-family:'times new roman', 'new york', times, se=
rif;font-size:12pt"><div>There was some discussion on the use of tungsten a=
s a balance weight, so I did some research on the density of various materi=
als - here is a list of approximate specific gravities:</div><div>Typical e=
poxy resin - 1.5</div><div>Aluminum - 2.6</div><div>Steel - 7.8</div><div>L=
ead - 11.3</div><div>tungsten - 19.2</div><div><br></div><div>It would appe=
ar that the higher density of tungsten would allow a more compact balance w=
eight, allowing the weight to be more concentrated to the extremity of the =
available space, reducing the overall weight. =A0But things are not usually=
 as simple as they at first seem. =A0In order for lead to be effectively us=
ed it has to be cast in a shape to fit the space, which is what I did. =A0I=
t is hard to get all the air bubbles out, but a lead casting can be
 reasonably dense. =A0The tungsten, however must be used in the form of pow=
der or rods held together by an epoxy matrix. =A0I don't have directly-rela=
ted experience, but I would guess that it would be very difficult to get a =
90% by volume tungsten mixture in epoxy (resulting specific gravity =3D 17.=
4) and if one was a little too casual and wanted to get an easily pourable =
mixture he could end up with a 50% mixture (specific gravity =3D 10.4), les=
s dense than a lead casting. =A0With reasonable care, which means careful m=
easuring of the epoxy and thoroughly mixing without trapping too much air I=
 would guess a 70% mix is reasonable and 80% is possible, but not likely. =
=A0In comparison, rods perfectly nested in a linear pattern, not hexagonal,=
 will be 78% "packed." =A0A 70% mix will yield a specific gravity of 13.9, =
23% greater than lead. =A0Will that reduce the overall balancing weight by =
23%? =A0No, because only part of that weight is at a small radius - the wei=
ght
 savings is more likely to be about 10% or less. =A0Is it worth the trouble=
? =A0It might be if an accurate lead casting is particularly difficult, but=
 otherwise I doubt it - at least that was the reasoning when I decided to u=
se lead.</div><div><br></div><div>Gary Casey</div><div style=3D"position:fi=
xed"></div></div><br>=0A=0A      </body></html>
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