Here is a description of what I was talking about and some ideas on
how you could build one. (Apologies in advance for the non-metric
measurements.)
SEEN FROM ABOVE: (how to build)
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
X X
X X
X ooooooooooooooooo X
X o ----------- o X
X o | | o X
X o | | o X
X o | | o X
X o | | o X
X o | | o X
X o | | o=======X===== vacuum line
X o ----------- o X
X ooooooooooooooooo X
X X
X X
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
xxx = flat board
ooo = routed groove
--- = sensitized material/negative sandwich
The baseboard could be made from any relatively thick wood with a
smooth surface. An ideal choice would be the sink cutouts that you can
get at almost any shop that remodels kitchens. I've seen then in the
surplus sections of large home depot type stores. These are about 3/4
inch thick fiberboard with a formica top and approximately 2x3 feet.
I imagine that if you wanted to do really large prints, you could
just buy a section of formica countertop.
Cut the groove with a router. No more than about 1/4 inch wide (1/8
should be OK too - It doesn't have to be large at all). Could be 1/2
deep I'd guess. The dimensions of the groove should be comfortably
larger than the dimensions of the sensitized material you want to
expose.
Drill a hole from the side of the baseboard so that it intersects the
groove at one spot. Figure out how to attach your vaccum hose to that
hole (what, you want the answer from me?)
That's it from the construction aspect.
CROSS SECTION: (how to use)
_________________________ mylar sheet
__________ film (neg or pos)
------------ sensitized material
XXXXXXX__XXXXXXXXXXXXXXX__XXXXX Baseboard w/groove
Place the sensitized material face up in the middle of the groove and
place the film on that. Over it all, place a piece of mylar that is
larger than the dimensions of the groove. I used very thin (like .001
inch) mylar that I got from a drafting supply house in a reasonably
large roll. The mylar is very "clean" i.e. free from surface defects
this way, and you can just throw it away when it gets too dirty.
Then turn on the vacuum. The mylar is sucked down tightly by the vacuum
in the grooves and literally molds itself against the
negative/sensitized material sandwich. I was surprized at how tightly
it held it down.
RANDOM THOUGHTS:
- As Larry mentioned in his post, you need some sort of bleed valve.
Shouldn't be too hard to fabricate. For example, if you placed a hard
plastic pipe in the baseboard coming out of the vaccum hole, you could
drill a hole or two in the barrel and expose or cover the holes as
needed. (And then you could attach a rubber vaccum line over the pipe.)
- Judy asked me what advantage this had over the sort of vaccum frame
that you typically find in platemakers, where the vaccum sucks a
flexible backing against the glass. I think that the differences would
be:
* Cost
* The potential for the thin mylar to transmit
more UV than the glass (As I said, I never tested
that, I was just trying to compensate fot not
having a more conventional vacuum frame)
* If you were exposing a stiff substance (like a
photo-etching plate), then having the flexible
part mold itself over the film rather than from
behind might give you a better contact.
- Larry mentioned another style of vacuum easel which is basically a
flat box with the top made out of peg board (i.e. lots of small holes).
Aside from the fact that this is slightly more complicated to build,
the one caveat I should mention about this style is that where the
holes are sucking vacuum from the image area of the sensitized
material, you will see some sort of distortion or densitiy in the
image. A workaround for that would to place some sort of stiff backing
down before you place the sensitized material/ film sandwich on the
easel. OTOH, the vacuum bleeding in this type of easel is much easier.
You just leave however many holes outside the image area you need open
and stick some sort of covering over the rest.
That's about it. Hope there is enough here for people to figure out
their own system. Please email me if you have any questions.
Carson Graves
carson@ileaf.com