Re: [CAD_CAM_EDM_DRO] Vaccuum table holes

In a message dated 07-May-02 07:21:10 Central Daylight Time,
davemucha@... writes:

> I am working on the table/platform of a router and want to hold parts
> with a vacuum.

Dave: I have done a LITTLE with vacuum hold-down, but nothing such as the
large manufacturers do, of course. The first method is a smooth, flat-top
table for clamping woodwork, NOT machining!) which had Formica top. There
was a 3/8" hole in the center, and two "V-grooves" heading "north" and "south
from that, about 18" each (was a 48" wide x 10' long table). When the wood
item to be glued was on top, we covered it with PVC "paint drop" and taped it
(sealed it) to the Formica with wide masking-tape. Then turn on the pump.
The PVC film "sucks up" into all the cracks, indicating seal and force.

The other item is a home-brew plotter (which does tracings of "CNC" programs,
for checking tool-bit moves before wasting metal!). Only a sheet of
grid-paper is to be held down. Professional plotters use this "vacuum grid"
method; that's where I got the idea. The top of the plotter is Formica,
again, and the Baltic birch plywood "sandwich" below is a matrix of saw-kerfs
to distribute the "vacuum" from a relatively-strong "muffin fan" to about
2000 #72 holes through the Formica. On 0.1" grid. A #72 drill is 0.025"
dia. This works good enough for my particular plotter, but the "professional
jobs" I have examined have maybe four or five times that number of holes (a
0.025" grid, with 0.015" Ø holes?).

I have had NO experience with situations I have only seen in pictures, where
metal parts are held down with RTV gaskets, etc., and 1E-3 mm Hg. vacuum,
etc.

Lotsa luck! Jan Rowland


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