screen printing > DIY - From master engineered marvels to cobbled together jury-rigged or Jerry-built junk!
DIY LED Exposure Unit
Pangea:
I do but I never hooked them up as I don't really have a use for them. I have a little jig I built to line up positives on the screen, it's not fancy but it only cost $30.
Fiodor Petrenko:
--- Quote from: Pangea on January 20, 2018, 09:49:44 AM ---I'm in the process of rebuilding my LED exposure unit and figured I would document it here.
Through looking at some tech sheets it looked like most emulsion crosslinks at about 395 nm wavelength. I was surprised to find this wavelength was available in inexpensive strips and 2 density layouts. I opted to get the densest at 120/meter rather than 60/meter because more = better, right?
I ended up using 11 34" strips mounted on a piece of coroplast that was then stapled to a box made of 1"x4"s. It looks pretty janky and like a fire hazard which is the reason it's getting rebuilt.
The power supply is 120v AC in and has two 12v DC outputs that are rated at 10 amps. The time controller was purchased on eBay and pretty much interrupts the 12V DC circuit when the time is up, shutting off the LEDs. The switches on the laser cut control panel turn all the power on, start the timer and turn on safe lights (yellow LEDs). I intended to purchase glass at some point but it was never needed because I use a space saver vacuum bag for exposure. For the new build I'll probably end up adding glass and a proper vacuum lid in phase 2.
I plan on reusing the time controller/switches and the power supply but not the LED panel or box. This time around I ordered 4200 LEDs because I want the strips to be much closer together like the M&R Starlight/Workhorse Lumitron. The strips will be soldered this time instead of using the crappy snap connectors and will be done in parallel to avoid differences in brightness. If they're wired in series the end strip has voltage drop and the whole exposure would be uneven.
So now for the before pictures:
Wiring Diagram
Turned on
Janky Wiring
Control Panel Mock Up
Control Panel Finished
First Tests (WBP Emulsion)
Switched to Cryocoat with 18 second exposure
Final exposure time using a Stouffer 21 step is ~80 seconds. I'm curious (and I'm sure someone here can answer) when companies are advertising their exposure units can expose in 10 seconds, are they using the 21 step guide?
Anyway, I'll update this thread when I start the rebuild and make sure to add any updated documentation (wiring diagram). Until then, ask any questions if you have them!
UPDATE:
Redrew the schematic during my morning coffee
--- End quote ---
Hi! I'm wondering if you used 5050 uv leds. I will try these and I'd like to know if they'll work fine:
Specification
Input volts: DC 12V (12V 2-3 A for 5meters 3528 300LED light strip)
Wavelength:395-405nm
Long life span 50,000+ hours
Protection Rank: iP 65waterproof
PCB Color: White
Is Dimmable: Yes(dimmer required)
Is Trimmable: Yes(cuttable every three LEDs)
Drive Mode:Contant Voltage
Beam Angle:120°
Viewing Angle: adjustable by mounting position
Working Tempreture:-20° to 50°
Size: W1.0cm x T0.25c
Did you tried the exposure unit on diazo?
Thanks!
Pangea:
I used 3528s that are spaced about 3 per inch, the densest I could find. WBP is a diazo emulsion and it worked just fine with longer exposure times (45 seconds-1 minute if I remember correctly). I've since switched to photopolymer and expose at 20-25 seconds but may switch back again to compare details.
Doug S:
Fiodor,
Thanks for posting the pics. I think you'll be much happier with the leds closer together. The pic you posted of the lights spaced out like that looks a lot like the lawson unit I bought "I've since went back to metal halide". The lawson was fine for the majority of the work I do but I wasn't happy with the halftone exposures. I know the starlight has roughly 10 times the leds which eliminates the cold spots.
Another thought: I admire you guys that have the knowledge to even attempt building your own because I wouldn't know where to begin.
Fiodor Petrenko:
Hey, Doug, how are you? The work is from Pangea, not mine, so props to him. I will be starting mine next week.
The widht of the strip i'll be working with is about 1 cm, so I'll put one strip (1 cm. empty space) another strip, etc. until i cover 1 mt. lenght.
As I measured, the space between every led light is about 0.65 mm. and the distance between the glass and the lights will be about an inch. What do you think?
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