You would do well to ask yourself what type(s) of prints you do. If it is mostly solid spot color with no half-tones, then unfiltered blacklight florescent tubes will work. If you do half-tones and very high detail, then a single-point light source would be better. In single-point systems, some use halogen (very inexpensive but generates a lot of heat and takes a long time to expose the screen because there is very little UV light), and others use Metal-Halide (the best source of UV light next to messy arc lights and/or the sun). In either case, the best thing to use is a vacuum blanket to achieve a good seal between the positive and the screen, but if you can't do that, a compression lid will have to do.
Use A metal-halide stadium light with as much wattage as you can find- mine's is only 400 watts.
You MUST use a rubber, vacuum sealed lid- this makes all the difference!
Also use a good inkjet printer with DARK black and good clear film-not vellum!
I got some cheap film off E-bay couple of weeks ago- u get what you pay for- sucks!
Good luck!
i dont understand, i cant burn halftones with unfilterblack lights?...dont most expensive units have these types of bulbs?...
or are you saying that they will come out better with a single point light!......or faster expose time?
I agree Single point light source is rock solid for most anything you'll be doing. Longer exposure time is only a problem if you have hundreds of jobs running....(I wish I had that problem!. Flip the switch and have a beer and relax 12 minutes is no big deal! I haven't used a vacuum table in a while since my pump broke. I use a heavy glass plate and it works fine.
I certainly appreciate all of the suggestions and help. its almost overwhelming trying to learn all of this stuff. I am thankful for this forum and the people in it.
I dont believe there is any difference between a vacuum blanket setup and a good "compression lid". As long as the positive is completely flat against the emulsion, its all the same(barring EXTREMELY fine detail).
ScreenPrintMan is right, unless you are running jobs by the second, why worry about exposure time. I use a 500W (single point) halogen that I bought from Menards for $10 and it exposes QTX in 5 minutes, every time.
The only time I run into problems is when I dont get the positive flat on the screen due to a lousy glass weighting setup.
If it takes 12min to burn 1 screen, then that's really an hour for 4 colors, plus set-up and inking up.
I guess for single color designs it might not be a big deal, but I couldn't imagine!
with blacklights you'll get undercutting and you'll lose any halftones 15% or less.
sorry i dont understand....15% of what? . the size of the dot or 15% of the halftone's.....i use a 500 watt halogen
and can burn halftones ,but not very small ones!..so at
the least enough of the tones wash out that i can still use the image...i just want to be able to burn half tones...better
then i do now...my buddy has a lumitron odessey unit, and
he burns halftones all the time on que!...i'am about to buy some blacklights , but if i'am goin' to spend the money i might as well make a single point mh unit right?....
Sounds like a combo problem with under exposure or poor emulsion coating and screen mesh is to large.
More holes per inch means smaller holes. Your dots need to be larger than the holes you're pushing ink through or they will be distorted. Make your dots larger and your film positive very opaque. If you go to higher mesh counts it will harder to push ink through the screen and you'll build new muscles. the previous discussion on percentages is a way of optimizing the grey scale visual impression.
Hope this helps....just one mans opinion. There are others who know way more than me, but this is from my personal experiences.
Sorry I forgot to add that I think you'll be happy with a single point light source. Why black lights? They are filtered . You want UNfiltered UV tubes. They operate at up to and beyond 360NM depending on the manufacturer. You don't need visible light. I still think a single lamp will work just fine.
sorry, i also forgot to add that they were the unfiltered blacklights, so would a 1000 watt halogen single point give me better results then say 8 to 10 48' inch unfiltered uv fluorescent lights , i got them lined up next to each other about a 3 inches from
the glass which is untempered plate glass.....currently i have regular fluorescents in there ,but they dont expose a screen for nothing, so i use my good ol' 500watt halo'.....i'd like to use metal halide , but i'am tryin to budget.....so maybe a halogen might be alot cheaper.......i built the whole unit and everything is nice but the bulbs...so i'd still like to use it!! and just put in the right lamps
thanks for your time and prompt responses i really appreciate it !!
building an exposure unit, any suggestions? 
DeAnna Rasberry
. Flip the switch and have a beer and relax 12 minutes is no big deal! I haven't used a vacuum table in a while since my pump broke. I use a heavy glass plate and it works fine.
