Re: [CAD_CAM_EDM_DRO]floating z axis

At 03:50 PM 5/23/02 EDT, you wrote:

>Bill: I have seen plotters, and have BUILT a couple using vacuum, but that
>REQUIRES that the blank be ABSOLUTELY-flat, preferably somewhat compliant,

as

>is paper! Further, drilling a PC-blank with FEWER than an average

hole-count

>opens up enough "leak" that even a 29.9" vacuum at the start would be
>useless.

Very doubtful!! I've had some real router experience, a big multi-head
Showa. We used it on ply and chipboard, and on multiple small chipboard
parts there is a problem losing vac. However, industry experts say you only
need 12-14" merc to make it work out and that was essentially our
experience. This is obtainable in the chip board despite a cut length of
say thirty or forty feet, times 1/2" width. With ply we were able to cut
complete 4x8' sheets into 4.5 x 6" blocks and with a few holes each to
boot, with vac enough to hold even the last ones. So if sufficent pump
capacity is on hand, a series of holes isn't going to be too tough.

As for flatness, if you have about that much vac starting, you don't have
to worry about the part being flat at beginning.

>table-top! Putting a "backup board" (waste) over the table, then the blank
>on top of that, would defeat the vacuum aspect in the first place!

Nope, we cut masks for the chipboard, which have a seal and port for each
part. You can probably use this trick with only a few ports in parts of
board that don't have many holes. But I think you're making more of this
than it needs.

There is one thing I had trouble making the shop people realize, and for
that matter the big boss too: dull tools will make all the diff. These
idiots ran their mills for months and wore several thous off cutting edges.
And parts started shifting radically, over time. In fact, they added a
second pump at $20,000 (ignoring my written analysis of the tool-drag
problem), with nearly no change in slippage. They didn't listen til one day
they were totally unsuccessful in a job that had run before w/o problem.
And it still took a call to a local furniture firm, who replaced cutters
each 8 hours, before they fell in line. You might want to keep that in mind
in drilling, though it seems a lesser problem.

>that is 12" x 19", what do you do, then, with the BULK of the unused
>perforated table-top?

Mask! It's so damned simple to just lay on a piece of cardboard over unuses
area, maybe tacking the edges with tape. How'd you miss that one?


Regards, Hoyt


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