I am looking for some detailed schematics of home made exposure units. Right now the way i do it is kind of ackward. I would like to build one that you can place the screen in close it and set a timer.
Pat
I burn with a home built exposure unit and get good results. My advice to you is to stay away from a timer, though.
It's more advantageous for you to build one that is has a single point light source to burn your images so you get less undercutting of your positive. You can get 1000w metal halide ballasts and bulbs at any hydroponic shop in town.
So long as you don't use a reflector (these normally come with the ballast and bulb) and you buy the right kind of bulb, you will get good results. I looked at the product information on Phillips' metal halide bulbs, and a 7000 degree kelvin bulb is one that outputs the most UV-A light.
Building a vacuum sealing top is not too difficult. Buy a sheet of neoprene (from eBay or from a screen printing shop) and glue it to a frame the same size as your glass. Hinge that frame to the unit, put some weatherstripping on the bottom of it to ensure an airtight seal.
Then, you can just drill a hole in the frame, stick some garden hose into it and attach the other end of the hose to a shop-vac with a universal tool adapter. When you turn on the shop-vac, the screen should be brought into intimate contact with the glass.
The only problem with this set-up is that hydroponic metal halide ballasts are not designed to be turned on and off very often and they take time to warm up. You have to put in a shutter under your glass that you can pull out. You would let the bulb warm up, put the screen and image on the glass, turn on the vacuum, pull out the shutter, and after the time required, push the shudder back in.
This is why I recommend staying away from a timer that would shut the ballast off between every burn, it's not good for the bulb. You kinda have to plan it so that you burn a bunch of screens at once.
I use this set up and can burn great 55lpi halftones in a 196 mesh screen.
Ok, that helps but i'm not sure where to place the lights, and also is the neoprene glued under the glass. How is the glass held into place. Just a few questions for now
Pat
Instead of neoprene, you can also use pond liner from Home Depot. It's cheap, tougher than neoprene, and convenient. You've gotta build in slightly more slack than with neoprene because it doesn't stretch as much, but it'll pull your screen and film down tight to that glass. I bought some, then ended up using neoprene. When the neoprene got too many holes in it, I figured, what the hell, I've got the pond liner, I'll try it. It's all I'm ever gonna use.
What are you using for emulsion? 2 minutes is impressive for a 500W halogen. I'll probably build a 1000W halogen this week. My black light florescent is just not making it.
He discusses the type of light source needed, the importance of using single-point source, and the proper distance of the screen from the light.
He gives an email address at the end where you can send for plans.
I built one of these, and it was very easy to build, inexpensive, and works fine (though I haven't tried it for anything particularly demanding.) My only complaint is that the halogen light is really freakin' hot.
Hi Bro...
I also used the same specs for my exposure unit. (Halogen 500W)
Coz i'm still new in this t-shirt printing, my exposure time is 5 minute...
So for 2 minutes exposure time from your quote, it is a really-2X good info there....
Hahaha...
I only coat one side so i can get the finer Detail and half tones with my home made Exposure Unit. in two mins ive been using it for about a year now and seems to work just like the good ones.
I've been researching metal halide. It's really not that expensive. A bulb, ballast and reflector is around $200 from the hydroponic store, give or take a few dollars. Add another $100 in materials for a metal cabinet with vacuum hold down frame and I should have a 1000W MH unit with vacuum for between $300 and $400.
Home Made Exposure unit 
good info there....
Re: Home Made Exposure unit 
