Re: Steel plate for hexapod bed

--- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers <rogersmach@y...>
wrote:

>
>
> If I were going to build a Hexapod, I'd use a welded frame

construction due to its "lanky" design. Use some 3X3X1/4 w/t or
2X2X1/4 w.t square tubing and build a hexagon and at the
intersections of this base weld an upright riser to attach the 6
actuators atop of each. Then tie all risers together at their tops
with anything i.e. water pipe, conduit, etc. Torsional stresses are
going to be the biggest issue and its inherent inability to apply
much force to the workpiece, the table/ work surface could be
pratically any type of sheet material (plywood even) inset and bolted
into the tubular hexagon base. That would be the cheapest route, just
some tubing and a welder. Use gussets at the joints and it would be
light, strong and rigid. Just another alternative. Granite surface
plates are very heavy and not very durable, they break easily.
1"thick plate base is redundant because the machine will never exert
those types of forces, 1/4" plate is too flexible.

>
> Ron

The idea that the fixed point of the arms need to be ridigdly fixed
should point out the need to also have a sturdy base.

Without a strong foundation the cutting force would bounce the
connecting points of the arms around.

The machine, like any, will be as strong as it's weakest link. In a
simple drilling operation, the pressure on the base would be like a
person drilling a hole in the floor. At some level of pressure, the
unit would lift itself off the mounts or at least start to flex them.

If one was to stick a corner of the 1.4 plate into a bench vice, so
that about 4 inches of it were held firm, a person could grab the
part and bend the plate. The ammount of force a person uses to push
will depend if the bend is just flex and will recover, or if it is
strong enough to make a permanent bend.

But, the amount of force is not very high. for a machine tool trying
to cut metal the flex will show up as chatter.

Once the machine is running and you start to test the envelope the
weakest links will reveal themselves.

Adding support to a flat plate is a rather simple matter, so the
ultimate base thickness is one that can evlove easily without having
to tear things apart.

Dave