Re: Digest Number 24

> Poured lead or type-metal bearings are still used extensively on some
> older-type industrial machinery and they are very successful - hence
> there are machines around here still running with them which are over > a hundred years old.

I am going to try something semi-related to this topic. My CNC is
fairly stiff for what I am doing, but I have a huge problem with
vibration. I am using aluminum and steel extrusions and box channel for
the frame. These hollow members are very underdamped in nature. 2 ways
to decrease the amplitude of vibrations is to either increase the
damping coefficient of the material, or increase the mass of the
system. I was lucky to spend a day with Dan Huggins, programmer of
Dancad, and he gave me the idea of making a precast concrete frame
components. Then I saw a company at a trade show (Philadelphia resins)
who make a slurry of granite particles in epoxy, and form it into a
composite that has much of the vibration damping properties of solid
granite. Davenport actually makes an entire lathe bed using this
process. They also fill structural members with this goo to help damp
vibrations in machines. Unfortunately, their stuff is too expensive for
a hobbyist like myself. But, I think I am going to try to fill my
hollow structural parts with a reinforced polymerized concrete. This
will make my machine heavy as hell, but should also decrease the
amplitude of the vibrations radically. I will let you all know how it
works.

-Mike Romine