Mercury Vapour exposure unit:

[Switch]

Here it is . I took our old fan off the halide, wired it in to the box, just to keep the glass/box relatively cool etc. My timer is ghetto, its a light switch (which you use to turn lights on for a set time when your out) . The actual box is a crate from a engineering company that used it to ship an engine. The glass as I say was the dearest at £50. The whole unit cost £60.

See the books, and a dark sheet to stop us getting blinded. My set up is of course ghetto, but take a look at my posters to see what I have achieved with it along with the emulsion I have used.

[Tom]

Posters look great. Ive been using a shitty diy exposure unit for 2 years (a 250w photoflood suspended with foam & glass for contact) with 20 min exposure.

I just want to build a good one this time. Im not that busy at the moment printing wise so its a good project for me to get my teeth into.

Would 1/4" tempered glass be enough for the vacuum lid?

[Switch]

Straight plain sheet glass. Tempered scatters UV. Sheet glass is lethal when broke, but it doesnt scatter UV.

[Andymac]

plain glass is the cheapest, 1/4" is fine. Tempered is OK, it just takes longer to expose, depending on it's UV blocking properties. It's more expensive, and can have roller marks from tempering.

if you can find some used glass from a big window getting replaced.

as far as vac no vac, the beauty of a vacuum top is you flick a switch, it sucks down, nice and even and no spaces. the ones I've seen lately, the rubber is attached to the top of the frame, the vacuum enters through the side. they are using a regular vacuum cleaner for this.
if you want to go 'compression', then hinge a top with a plywood sheet covering the frame edges, clamps in front, and make it slighly higher than your screen frame. then have a piece of foam wrapped in black cloth (or a couple of diff sizes for diff screen sizes) and you just stick that in the centre of the screen, then close the lid. the plywood compresses the foam into the screen mesh and pushed against the glass. Easy.

I built one from scratch years ago and used the valve off a truck innertube, take out the stem and glue the base to your rubber blanket, connect to pump with clear tubing.

It's all good.

[Fools Gold]

Vacuum top is the best thing ever. When I got my big vacuum frame my exposures got about 100x better and more consistent. But I think there is something up with the glass, my exposure times went from 3 minutes to about 15 .. . but the results are so much better, and I can do two frames at once.

[Tom]

Okay so plain 1/4" glass. Thanks.

I did a step test today with the lamp 32 inches from the glass & optimum exposure was between 3 & 4 mins. Im delighted with that as my time with photoflood set-up is 20 mins.

I also have a blow pump for an air mattress here. It deflates too. Reckon its
powerful enough for a vacuum lid? I deflates a 2 litre coke bottle real good.

[Tom]

So I spent the weekend making my exposure unit. Its done & im delighted with the finished product. Thanks to all for the info.

The box:





Interior all painted:




The 400w Metal Halide lamp:




The cover for the light area:




Inside finished unit (with two fluorescent lights for set up & spotting out):




Wiring it up:




The finished product:








Breakdown of costs:

Metal Halide lamp: 120 euro
1/4 inch glass: 50.00 euro
Fluorescent lights: 30.00 euro (15e each)
Digital timer: 11.00 euro
Power strip with switches: 16.00 euro
Plywood: 50.00 euro
Trunking + wiring & plugs: 8.00 euro
Castor wheels: 6.00 euro (1.50e each)
2 x 1.5 plained wood: 10.euro
White paint: 7.00 euro
Black paint: 11.00 euro
Roller tray & gloss roller: 2.50 euro

Total cost: 321.50 euro

I didnt actually spend that much as I got the ply for free but thought it was important to add it in to show what it really would cost to make.

[Switch]

Tom thats class. I like the digital timer. Tried it out yet ?
I see the glass costs as much as it does over here.

[Switch]

One suggestion - the box needs a vent some place , as the temp of the lamp will make the box super hot. Not good for the glass or box sides. Apart form that I dig it.

[Tom]

Yeah Ive tried it out. Its amazing. 4 min exposure time. Bulb is 38" from the glass.
Re: Heat - I had it on for 15 mins straight yesterday & no sign of any over heating & no funny smells either & my actual burn time is 4 mins so I dont think there is any need for vent holes. Will probably fit a vacuum lid at some stage in the future.