I'm new here but I have been looking at all of the exposure unit threads. I plan on building a unit about 4 feet long and roughly 3 feet wide, using six 4ft tubes. I have been researching which bulbs to use and have a pretty good idea of what I need. I was looking at the F40T12BL (would order online, can't find them in stores) since the general opinion is that unfiltered black lights are the way to go. However I have heard mixed opinions on whether or not the filtered black light bulbs (which can be easily found in stores) will work. I was also wondering if the F40 Plant/Aquarium bulbs from GE would give off enough UV for exposing. I'm trying to keep my exposure times in the 3-5 minute range. Just want to make sure I am getting the right stuff before placing an order. I was planning on using fixtures that have a plug on the end, hooking them all up to a power strip and running them that way (not sure if that would trip a circuit). I'm also aware of the need for non-protected glass.
I've always heard unfiltered black lights are the way to go for this design. They can be ordered online. However, I have heard of success with the black light tubes you can get at Home Depot and places like that.
The exposure units I have made personally were always with halogen work lamps. They're actually quite a bit easier (you can definitely chain them together with a power strip) to set up, and you'll get excellent results. For a 3x4' area, you'd want at least two 500-watt lamps (safety glass removed). I know that might not be in the information you're looking for, but I wouldn't rule out the halogen exposure unit. They're simple and highly effective.
I use the F40T12BL bulbs and they are def the way to go. I think I have 8- 5 foot bulbs and the exposure times are 90 seconds at the max, usually less. If you can swing it I would also recommend building a vac blanket well.
Thanks for the answers, i'm gonna go with the blacklights and 1/4" glass. Gonna put the vacuum blanket on hold for now, although I would like to have one. My print professor told me that sandbags (or similar pliable weights) work well for good transparency contact.
I use 4' unfiltered black light tubes and they are fantastic. Beauty is, you can put them 2-2.5" away from the glass which allows my exposure unit to be only 8" deep and an extremely portable countertop unit. I just framed it with 2x3's and faced it with 1x8 pine, sitting slightly higher than the 2x3's, to make a lip for the glass. Simple. It's also really easy to build one into an existing countertop. Just hang a regular fluorescent fixture or customize your own.
As for the vacuum lid, I spent $250 at a local Vancouver shop for (2.5"?) square hollow aluminum tubing to be cut and welded into the size of the frame, to drill holes a few inches apart all around the inside face, to weld a port with a stub of pipe to fit my vacuum hose (2") -this can go anywhere you want- and they even welded strips with bolts to the top face, and another set of strips with drilled holes to use as a pinch frame for the rubber blanket. (hard to describe, but it's just a smart way to be able to put in or remove a blanket, repeatedly...cause you don't want to drill into the frame..) Works amazing.
In the 4min20sec arena for exposure times....anywhere up to 6min for tshirt screens and old emulsion.
I got my exposure figured out and 15 minutes is about the minimum I need to harden my emulsion through 20lb paper. What do you guys use to ensure good contact between the screen and your transparency? After testing exposure times, it was pretty obvious that the edges weren't crisp and were more rounded. Also, I don't have a vacuum blanket, so that is not an option.