 Re: Home Made Exposure unit
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. |