At 09:44 PM 3/21/2009, DJ Delorie wrote:
> converted my UV exposure box to vacuum hold-down.. . . the glass bow in so
>much I feared it would break!
i've built several vac hold downs over the years and the trick is to
have the substrate supported everywhere. one way i did this was to
take a piece of good quality flat plywood and cut parallel groves
with a table saw in both directions about 1/8 inch deep on one side
across the entire face of the board. (say, 1/2" apart) spray it with
acrylic or some other sealer to seal the wood, drill a 3/4" or
whatever size hole you need to connect to the vacuum line in the
center of the board and then glue a piece of Formica on the top of
the grooved side carefully so's not to get glue in the grooves (i
used contact cement on a 2 ft x 3 ft table that lasted over 20 years
for screen printing). now you can see from the edges where the
grooves are and draw pencil lines across the formica and use these
guides to drill 1/16" holes across the entire surface over the
grooves beneath. now tape up the edges to seal the ends of the
grooves and attach the vac hose (maybe with a 90 degree connector).
you will have to put wooden feet on the bottom so the hose can exit
from beneath and keep the board sitting level. now whatever size
board you place on the top, just tape around it's edge to seal off
the uncovered vac holes and any size board can be accommodated. if
you want to expose negs to photoresist, you can also place a piece of
flexible clear plastic over the top of the board/litho neg sandwich
that covers the entire hold-down surface and get perfect contact for
exposures. i used to use sunlight to expose and place a toy dart
stuck on the top edge of the board to orient to the sun. when you
move the board so that the shadow of the darts shaft disappears, the
board is exactly perpendicular to the sun's rays. i now have access
to some free corian and will build one from that which has a
perfectly flat and smooth surface.
William Alford
GI Motility Medical Research Page
http://alford.grimtrojan.com/ [Non-text portions of this message have been removed]