Re: [CAD_CAM_EDM_DRO] RE:Need a vacuum system for acrylic sheets

In a message dated 1/12/2005 9:13:54 A.M. Central Standard Time,
skotze@... writes:

I am using bullet catches through MDF (actually melamine) with about an inch
of vacuum space. Is there a better way[?]<<
In '74 I wrote an article for a pipe-organbuilders' periodical about using
vacuum for flat-stuff clamping. Hate to use the cliche, but, "Been there;
DONE that!" You do NOT need "space" for the vacuum! It has NO mass nor
dimension, and even when the "bag" seals-down ot the table-surface or whatever, the
% of vacuum "all inside the bag" is still the same! If there is a tiny leak,
any offending air will "hiss" right under any places the "bag" is "sucked
down" and the vacuum will remain constant all over!

The ONLY way for the vacuum hold-down system to work is to use sufficiently
thick or "air-proof" plastic, WIDE tape to hold it all down, with NO "folds"
which produce open creases, and a solid little vacuum-pump. Better it run at
"only" 29 mm Hg and be only a 1/4 hp. machine than to be a 5 hp machine which
runs at 28 mm Hg! Common sense! Vacuum is NOT magic. Has NO mass. Is
NOT "particles" (matter). It can NOT be seen! (One can ONLY see the "effects"
of vacuum!).

MDF may SEEM like mighty solid stuff, but it "breathes", and using that as
"one side" of a vacuum-hold-down lash-up may-well cause failure and
frustration! Glue FORMICA on the top side of your MDF table-top! Besides, that
surface will allow taping the "bag" down more properly! That will DOUBLE the
effectiveness of a larger area. These days, SEVERAL organbuilding firms use
vacuum-clamping with PVC "paint-drop" sheets and 2" masking-tape! I have seen 2"
duct-tape used for this and asked, "WHY?" and was told, "Well, it COSTS a lot
more, so it MUST be better!" The gene pool is leaking!
Near-expiration-date masking-tape is quite good enough! A semiconductor hermetic seal is NOT
essential for this application!

Jan Rowland, OLD [deleted]





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