Re: Ball screw cost and sources - Moglice - Phillycast - concrete

You can always make just a decent slab of concrete (cure for a
month), make sure it's level, put a liquid-tight dam around the
edges, and pour in some liquid surface plate...

http://www.precisionepoxy.com/PlateInfopg4.htm

The CMM I had was a gantry type machine that used a field-built
concrete inertia block as the structural base/floor of the machine.
It was 12 feet x 8 feet x 5 feet thick, and filled with 3/4" rebar
layed in a 4" x 4" grid at every 4" of depth (that's a lot of
rebar). The four machine pillars sat on embedded 18" x 18" x 1"
ground plates that had big J-hooks embedded about 3 feet into the
concrete. The standard base was about 3 feet thick, but ours was
spec'd special to handle 80,000 lb. dies without deflecting the block
and tilting the top of the pillars (about 4 feet tall, with the x-
axis beams at the top of them) a zillionth of an inch. You know how
flimsy those cheapo 3 foot thick concrete slabs are! The concrete
had to cure for a month before the machine was assembled, aligned and
calibrated. A year later, at the 2nd calibration, the machine mapped
almost identical to the 1st... proving the concrete was incredibally
stable.



--- In CAD_CAM_EDM_DRO@yahoogroups.com, Stephan Kotzé <stephank@c...>
wrote:

> Hi guys
>
> I have also been toying with the idea of using a concrete cast

reinforced base. A few OEM machine builders use them in their
machines, as concrete has excellent vibration absorbing properties,
and is used in high speed milling machines. My idea was to use a self
levelling screed to give the final flatness. I was planning on using
a orbital sander to "tap" the mould during the initial cast to get
rid of trapped air bubbles, and during the screed pouring to let
gravity along with the tapping action give me a perfectly flat
finish, essentially water level.

>
> For the main beams, I was also planning on pouring concrete into

the square tubing to stiffen them. Problem is the binding of the
concrete to the inside of the tube. I thought of using some studding
running through the tube with two endcaps and a couple of bolts to
pre-stress the whole unit, the same way pre-stressed concrete
flooring slabs are manufactured.

>
> Stephan
>
>
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