Re: concrete/molded structural elements

> Message: 2
> Date: Thu, 27 May 1999 07:30:06 -0500
> From: groehm@... (Geoff Roehm)
> Subject: concrete/molded structural elements
>
> Mike Romine
> wrote:
>
> >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

[]

> >I think I am going to try to fill my hollow structural parts with a
> >reinforced polymerized concrete.
>
> Not being an engineer, I ask your indulgence if this suggestion is
> stupid, but how about foam-cored structural members, molded from a
> Corian-type material? Advantages would be lightness and easy machining
> with common tools, but would they be strong enough? Would the foam
> cores help to "increase the damping coefficient" of the
> material/structure?

I saw formula once for strength in tubular structures, something to do
with the difference between the outside and inside diameters, and the
conclusion was that filling a strong walled pipe (in that case it was
carbon fibre reinforced plastic - used in kites) with lighter, weaker
stuff (foam?) would not affect the bending coefficients much at all.

So I think your molding will need interior struts to increase the
damping, which is hard to achieve effectively with a molding process,
and you might as well make them solid parent material.

> On a related question, how would reinforced concrete work for the bed
> of a largish (5' x 6') CNC wood router?

I would rather use a welded frame covered with sacrificial chipboard,
then at least you don't lose router bits to your bed material (so
often) (-:

Something like the one shown here
http://www.super-tech.com/root/rr.htm

> Geoff
> Tennessee

steam and wind

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