Re: [CAD_CAM_EDM_DRO] RE:rE:re:Re: not stiff enough! (machine design considerations )

I have made both types- gantry and bridge.

The advantage of gantry as I see it is stationary work. If it
is rack and pinion drive or similar, the x (base) rails can
be grouted right in to the floor. Gantry travel can then be very long... 20
feet or more if you need it. For smaller gantries
heavy or long work can be machined then shifted down with further machining.
Just in case you want to carve dugout canoes or make airplane wings. :^)

Bridge is usually easier to construct. X can usually be driven by a single
screw due to the favorable bearing force angles. It does not require the
massive stiff construction needed on the gantry feet to preserve stiffness
at the spindle.

Of course the ultimate is a hexapod. I would like to build one
but I did a quick cost estimate of constructing the gimbal
assemblies and found it to be much too expensive. It required
I think 48 high precision preloaded bearings. That's some big
bucks. The gimbals need to be precise as it operates near
poles.

I understand EMC is capable of doing the hexapod maths.


Many, many machines at the 2000 IWF show were double
table bridge. One table is cutting while the other is loaded/
unloaded.

In my work the added versatility of gantry for very long work
is worth the extra cost. As long as I reregister the work accurately when I
shift it down only the building walls limit
the length.

Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.rabun.net/~leswatts/wattsfurniturewp.html