screen printing > DIY - From master engineered marvels to cobbled together jury-rigged or Jerry-built junk!

DIY Exposure Unit Question.

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JackThrasher:
I am building an exposure unit and I am planing to put a 400w Metal Halide bulb in it. Ant recommendations as to the distance I will need from the screen? And would I be able to burn halftones with that type of light source?

Frog:

--- Quote from: JackThrasher on December 27, 2013, 02:56:24 PM ---I am building an exposure unit and I am planing to put a 400w Metal Halide bulb in it. Ant recommendations as to the distance I will need from the screen? And would I be able to burn halftones with that type of light source?

--- End quote ---

For distance, assuming that you have no specially designed reflector, the rule of thumb is 1.5 times the diagonal of your desired exposure area.

As for halftones, they are much more a product of how closely you can press the film to the emulsion.
Vacuums are the single biggest improvement in holding resolution, and reducing undercutting.

Surprisingly though, for many non-demanding jobs, many folks do pretty well with units designed with foam and draw-down latches.

JackThrasher:
So should I build it with a diagonal reflective surface from the light source to the glass? Or should that be black, with a reflective ballast? The NuArc 2000w exposure unit I use at my day job has it set up that way... Would that be a good BluePrint to follow design wise?

Northland:

--- Quote from: JackThrasher on December 27, 2013, 02:56:24 PM ---I am building an exposure unit and I am planing to put a 400w Metal Halide bulb in it. Ant recommendations as to the distance I will need from the screen? And would I be able to burn halftones with that type of light source?

--- End quote ---

I converted a fluorescent unit (15 lamps) to metal halide a couple years ago.... I chose to use three 400w lamps, because I wanted to get plenty of curing punch. Some have suggested the multiple lights sources  is a huge no-no, but I prefer to deal with the chance of undercutting and avoid underexposed screens. I found 400w fixtures (with lamps) for $25/ea, so it's a pretty cheap retro.

If I stumble across a 1000w MH fixture, I'd back up and redo the thing.... but for now, I'm enjoying better screens than my old beamed blacklight fluorescent provided.

Photos:
http://www.flickr.com/photos/northlandsp/sets/72157625703927040/show/

screenxpress:
Man, you always have some of the neatest DIYs and your presentations/explanations are always top-notch!!

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