Re: [CAD_CAM_EDM_DRO]floating z axis

In one of my alter egos I am a cabinet maker and use vacuum quite
extensively. You have the option of using either high volume/low
pressure, as per shop vacs, or high pressure/low volume, such as the
GAST rotary vane. If you are holding a large surface area a shop vac
is fine, but if I was routing a smaller areas, such as PCBs I would
use a GAST. On a 6"x4" pcb with a shop vac @ 14" mg (7psi) you get
148 lbs of hold, with a GAST @ 28"mg (14psi) you have 296 lbs.

Personally I hate all the mess associated with ds tape and use vac
almost exclusively and for small parts tape doesn't hold any where
near as well as vac.

If I were doing this type of work I'd use a vac vice to rout the
boards and then use edge clamping to drill them.

regards,

Bernard

--- In CAD_CAM_EDM_DRO@y..., bjammin@i... wrote:
> 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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