mdf for machines was Re: Vacuum Table

Peter,

Mdf can make fine, long lasting furniture; IF its' inherant qualities
are considered and accounted for... This is no different than the
consideration which must be given to solid wood construction.

When MDF "moves" due to humidity changes it moves fairly equally in
all directions, whereas wood will move twice as much width vs.
thickness(tangential vs. radial), depends on grain direction. An
eaxample: Quartersawn or vertical grain is often specified for drawer
sides since it tends not to cup or warp, BUT the grain direction
going through the thickness of the board means that vertical grain
stock will change more in THICKNESS than in width (per unit). For
High grade drawer construction(without mechanical slides) this
matters...

Wood ALSO moves more in BOTH width and thickness (regardless of grain
orientation) than in length. What solid wood offers that is missing
from mdf is stiffness, due to the grain fibers running the length of
th solid wood stock. This is sometimes handled by mfrs laminating MDF
onto a plywood or oriented strand core. This retains the stability
and finish of the mdf while at least "improving" the stiffness over
plain mdf.

MDF is dense and damps vibration very well when used in machine
construction. It has a tendency to split when fasteners are driven
into the edge without pre-drilling. (so do many solid woods!)
Compared to Jon K's choice of plastic, it is cheaper (but must be
finished (sealed)to have a long, stable life. It will damp vibration
better. But its surface is not hard enough to use for axis movement,
whereas the plastic could be used this way.

Of course, as always the size and use of the machine need to be
considered; and a "blanket" statement about "a" being BETTER than "b"
is doomed to failure, IMO...

Hope this helps.

Ballendo

--- In CAD_CAM_EDM_DRO@y..., cadcamcenter@y... wrote:
<snip>
> Very popular with the furniture manufacturer because it
> comes in large panels and has smooth surface, and when
> painted/laminated, makes beautiful furniture in the show room, but
> which does't last. Give me solid wood anytime. Further, the MDF
> will change dimension with changes in atmospheric humidity.
>
> Because of its relatively poor resistance to water and dimensional
> stability, I just wonder if John Kleinbauer have hit upon a better
> way of making home-made CNC machines with grey platic, compared
> with those like Dave Rigotti, etc. who use MDF. Any opinions CNC
> old-hands?
>
> Peter