Re: [CAD_CAM_EDM_DRO] X axis load cantilever?

Replies interspersed

> I've just spent a few hours with pencil and paper, doodling out some
> layouts for my (theoretical at this point) PCB mill/drill. I want
> to have roughly 18" x 18" usable area, for the Y and Z its not a
> problem (gantry style) but for the X axis I figure I'll have to get
> MUCH longer leadscrews and rails. But how much longer?

> 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 believe it is not called a gantry unless it moves, so if you plan to have
a moving table it would be called a bridge.

>
> 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 have a picture in the photo section of my 20" X 20" router with a moving
table, similar to what you want. It is under the folder Bills Router. The
distance between my 2 bearings is 3" and the length of each is 2" so with a
20" table I have ((20 - (3 +2 +2 ) / 2) = 7 " of overhang on each end of the
table. I have done wood, plastic, aluminum, ceramic tile, and stainless
steel on my machine, although I wouldn't recomend the last two on a regular
basis. If you are going to be doing PCB's you will have no problem with a
similar setup. You can probably get by without any problems with a 3/16" or
1/4" table although 1/2" won't hurt, it will just require a little more
power. I am using THK SR15 linear bearings on my system. Also you should
have a floating spindle if you are going to rout PCB's

Bill

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