Re: [CAD_CAM_EDM_DRO] X axis load cantilever?

On Thu, 4 Sep 2003, ghidera2000 wrote:

> If I fully support the 18x18 X-axis table with say, 6 linear
> bearings, one in each corner and one in the middle, I'll need a X-
> axis length of roughly 36" + bearingwidthsetc in order to access the
> entire PCB. I can shorten that by pulling the corner bearings
> towards the center and letting the ends of the table hang in the
> air. If I used something like 1/2" aluminum for the table, how much
> overhang do you think I might be able to get away with? Keep in mind
> I'll just be doing light work on this.

I agree with Dave. For PCB milling I don't think you need to have the
table supported at the corners. You should be able to get away with a
fair amount of overhang.
Especially if you make a floating head for the spindle. I think that's
how most PCB routers are designed anyway. The floating head has a 'foot'
that rides on the surface of the PCB, and the cutting bit is set at a
fixed depth in relation to the 'foot'. That way the whole Z axis moves up
and down and compensates for small amounts of table deflection and
differences in thickness in the PCB material. What you want for PCB
milling is a constant depth of cut from the surface of the material, not a
constant thickness like you would get on a 'normal' milling machine.

Also I think a 1/2" aluminum plate is too think and will be unnecessarily
expensive. I would use a 1/4" aluminum plate and put supporting pieces
uderneath like joists under a floor.

> I also considered a stationary table and moving the gantry - but
> that looks a bit scary... Have to use two matched screws and timing
> belts etc.

I think the stationary gantry and moving table would be easier myself.

C|