screen printing > DIY - From master engineered marvels to cobbled together jury-rigged or Jerry-built junk!
DIY LED Exposure Unit
blue moon:
--- Quote from: mimosatexas on January 24, 2018, 10:26:38 AM ---if the angle is 120, that would mean the ideal distance sits closer to an inch away max unless im missing something
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it would depend on the LED spacing. The further apart they are, the further the glass has to be . . . Vastex unit still has the best field I've measured (data is kinda old now though) and their unit is about 6" away.
pierre
Northland:
This post caused me to look a little closer at my exposure unit. I'm using a DIY LED that is about 300 watts of 5050-SMD diodes (1500 total)... that are mounted 1.75" below the glass. The spacing between diodes and rows of diodes is 16mm (5/8") and covers about 18" X 32" in total area, so it's a pretty tight pattern. I don't know what angle the diodes broadcast at... but I think the 1.75" distance between the diode and glass is a good compromise between even exposure, without too much undercutting.
The nature of my work is predominantly simple spot color stuff... so I've never really investigated it's maximum capabilities.
For a long time I burned S-mesh screens at 15 seconds.... but changed that to 45 seconds to increase durability (I catalog a lot of my screens for re-use and the removal of tape was pulling emulsion from the edges of the screens). The longer (45 second) exposure time fixed that problem.
I've just burned a 180S, using a Chromaline test film, and I would say the dots between 10%-90% we're really good... and a 6 point font looks good too.
The 90% to 100% range looks the same (fully Open) and the 0% to 10% range looks the same (fully Closed).
Maybe I could squeeze a couple percent better by adjusting the exposure time, but that's a capability that I haven't needed, yet.
So.... I'm guessing that a decent DIY LED will require about 75 watts of power per square foot.
And, the spacing between diode rows should be the same as the spacing between the diodes on the strip.
The quality of LED strip is questionable.... I needed 15 meters of strip to get 10 meters of uniform product, but it's cheap so that isn't a deal-breaker.
Pangea:
--- Quote from: mimosatexas on January 23, 2018, 12:19:00 PM ---Based on the last image, isnt the glass pretty far from the bulbs? Arent most of the LED units closer to like an inch or two from the glass vs 4 to 6 like in the image?
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Yes, I had the panel about 4 inches from where the screen rests for exposure. I've never seen an LED exposure unit other than photos and those weren't too helpful in figuring out the proper distance. I exposed a new test screen this morning and raised the panel up 1.5" higher to see what would happen. The Stouffer test came out at a pretty solid 9 with 25 seconds exposure on a 305 with Cryocoat emulsion so I could probably cut it in half and hit a decent 7.
Here are some photos:
blue moon:
going to 7 from a 9 requires doubling the time rather than cutting it in half. Or am I missing something?
pierre
Pangea:
Other way around. I'm aiming for a 7 but I'm at a 9 (which is slightly over exposed).
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