Originally Posted by
Eldon_Joh
Cast iron has at least ten times the dampening coefficient of steel, perhaps 100 fold, and steel has a higher dampening coefficient than aluminum by perhaps a factor of 10, except for certain cast aluminum alloys which have high dampening coefficients. Epoxy granite may or may not have a higher dampening coefficient than cast iron, when you account for its density and stiffness. it depends. its modulus of elasticity is also a huge variable. epoxy for instance iirc is 100 - 200 times more flexible than steel. so if there's 10% more epoxy than needed your epoxy granite may be half as stiff as it could be, as the modulus of elasticity of granite is 40 times that of epoxy and one 8th that of steel. so until you measure both the stiffness and the dampening coefficient of the EG and make it a repeatable process its not really appropriate to make statements as general as you have made, and of the documents i've read, i've found a variation on the order of 10 one person reports 40GPA, the other 6 for the modulus of elasticity of epoxy granite.
But it is the modulus of elasticity divided by density, multiplied by the dampening coefficient that matters.
Cast iron actually wins for the most part. There are a couple other materials that can do better but they are expensive. like a mixture of indium and carbide particles iirc which has a dampening coefficient of something like 0.5 but its horribly expensive.
where epoxy granite is of most use is when its not possible to get a cast iron casting made (mostly limitations regarding what the foundry is capable of doing). so for years now many machine tools are made by filling the inside of the cast iron castings with epoxy granite. -but you only apply as much as you need. filling the machine solid lowers its resonant frequencies and that is often not what you want.