Re: [CAD_CAM_EDM_DRO] Re: vibration damping materials

Our ShearDamper system (ITW Philly Resins) was developed by
none other than Dr. Alexander Slocum. It allows a structural steel
member to be highly damped , very stiff, and light weight.
Modern machine tools are designed to be stiff but light, like
an airplane structure.

In the old days before modern computational techniques the usual
method was just to use huge chunks of iron.

Damping involves getting a mechanical impedance match between the
energy absorbing material and the structure to be damped. What
the heck is that? Well, I will try to avoid reams of math here and simply
say that the forces needed to deflect the damping material need to be
of the same magnitude as the forces needed to similarly deflect the
structure.

So damping material for structural steel shapes really has to be quite
stiff.
It's easy to see that a surface coat of car undercoating doesn't supply
much deflection or velocity force reactions compared to a quarter inch
steel wall. So very little damping will occur. (lots will occur on 0.015"
sheet
though- it's a better match.)

The damping materials can be made appropriately stiff by constraining them
in a sandwich between two steel members. Since it is virtually
incompressible
it is forced to shear and absorb energy.

So that's how ShearDamper and other systems work. I have to admit
that there is a problem though... our damping compounds are too expensive
for most hobby use. Epoxy and urethane resins are often over $200/gal
these days.

I also think dry sand might be an economical alternative. For many
applications
portland cement type concrete is too unstable for machine tool use. I have
seen it used some, but consider that even after curing concrete has huge
changes in dimensions with changes in humidity- kind of like wood.
That is why polymer concrete was developed.

Les
Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.alltel.net/~leswatts/wattsfurniturewp.html
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