"Karl Townsend" wrote in message
...
....
There are a few ideas in there but, frankly, those guys are mostly not up
to
speed with this material. The machine designer who complained about cracks
in the polymer concrete reinforced it incorrectly. Most of the others are
talking about making sheet metal structures and trying to beef them up
with
concrete. That's really not what I'm talking about. That's been done for
...

Yea, I know what you mean. its a bit like mining gold. You got to
shovel a lot of ore to find that nugget. My hobby time has morfed from
cutting metal to rebuilding old CNC iron to like new with a brand new
control. Among all the idiots, there are a couple gems.

For example, I learned that my old wire EDM is the best possible
candidate for upgrade to a new control and I found a guy that knows
this machine like the back of his hand.

Say, I think the project after this is to build a four foot by ten
foot Plasma, torch, router combination machine. I'm thinking weldament
for the machine frame. Does this technology have any benefit for
vibration dampening on this application?

Karl

Yes, concrete is a good vibration damper and you could make an effective and
inexpensive router frame out of it. But it would take some real
understanding of the material to avoid potential problems. And a good
structure is not going to be light.

For something like that I'd look at prestressed concrete sections that are
available commercially. If you wanted a perimeter frame, you could use small
beams, which tie together with special mortar at the corners. Or, if you
wanted a slab, you can buy hollow floor slabs. These things are heavily
reinforced and prestressed so that they'll handle a lot of tension loads.

But after it was built, I don't think you could move it without wrecking it.
That's one of the limitations. Small, squat machine tools are one thing.
Larger structures are another.

Some of the first machine tool applications were oil-country-type lathes
built by the Soviets back in the '40s, so big machines are entirely
possible. In fact, that's a major attraction of concrete for machines. But
you pretty much have to build them in place. Unlike cast iron or steel, they
have to be built for the specific loads they're going to be subjected to.
Put a forklift under a long span that's stressed for heavy loads from the
top, and you can crack it.

Small machines, like a lathe chucker or a squat bridge-type mill, are an
entirely different story. You can build them with ferrocement and they'll be
capable of handling stresses in all directions. And they can be much lighter
than girder-type structures. The material itself, loaded with a dense matrix
of welded steel mesh, has an overall density similar to that of aluminum.

A big frame like your router idea is something for one's second or third
project, IMO. It's a challenge unless you've been designing bridges all of
your life.

--
Ed Huntress