DIY exposure unit: any plans or advice appreciated

[Wildcard]

Following on from one of my previous posts about my crusty old home made fluoro expo unit, I've been considering a fresh build rather than trying to renovate the current model. I'm hoping to tap into the knowledge bank of some of the DIY gurus here.
Basic requirements and factors:
- biggest frame size is 23.5"×31.5"
- floor space is under a staircase, in a corridor, so the vertical swing vacuum table with separate light unit won't work - it needs to be a table top. Vac top may not be able to open all the way up as a rigid frame because of the stairs above.
- mostly just shooting basic spot colour screens, but I'm playing with halftones more and more so I'm hoping for a real step-up from my box of fluoro's.
- emulsions: Kiwo poly plus SWR red (diazo), and also Ulano Orange (SBQ)
- high humidity climate and low to medium runs on screens. 99% plastisol inks.

Topics I'm looking for advice on:
- best light fixture options. Ive decided to move away from fluoros and get a point light source. I'm assuming the metal halides and LED floods available at the local hardware store or lighting shop are not good enough, so would the fixtures aimed at hydroponics be appropriate?

- vacuum blanket setup. Recommended type of unit and setup of the vac unit, and any fiddly things to consider. I've read some topics on the blanket and seems like a nylon lined neoprene is the go.

- general build advice. Anything that might be important to consider that is not common sense, ie.  Air flow around lamps etc.

I hope there is enough back story here to paint the picture, and I would really appreciate any sound guidance. Thanks in advance.

James

[Maxie]

I've built a few.   Recently changed my table from fluorescents to LED.
For a light source contact Greg at Saati, they have a 300w LED that is great.   Amazing for the price.
Just put it a little above a lean floor, it has fans in the back.
When you build the vacuum, make the glass bigger and have a rubber strip pushing up against the glass to give you a seal.      I tried sealing against a metal frame and it kept leaking.    The glass is always smooth and flat.
The lid can be made out of metal, I used 11/2 x 11/2. You can put the rubber blanket on the outside of the metal and connect the vacuum to the metal frame.    Drill a few holes in the metal for the vacuum.
Most of the vacuum table suppliers will sell you a blanket.
Connect a nylon cord neat the hole and lay it over the screen so the vacuum works inside the screen.
Make sure you get clear hardened glass.
I have mine set up with two timers so that the vacuum works for a set time then the lamp switches on.    They switch off together.
If anything isn't clear I can post photographs.

[Wildcard]

Thanks for the info Maxie. I'm probably most curious to know what specs to look for in the vacuum pump and the lamp.
I've found a supplier for low iron glass, the box is simple enough to build, even the blanket doesn't worry me too much.
I've looked at some local hydroponic suppliers for a lamp and they have mh and led options that might work, and I'm intrigued to know if the big led floods at the hardware will be better than fluoro's. I'm not sure it will be good value to import a lamp or fixture from the US, but if it's the key that unlocks the secret door to good stencils then I'll consider it.

And of course photos would be great if it's easy but please don't go out of your way.

[Homer]

wildcard, where are you located? I have a douthitt unit I will give you - search the ads here for pictures I posted up a hwile ago - , has integrator, excellent vacuum top, glass, the only thing is the bulb won't fire. drop in a new light source and you have a nice unit....pay freight, it's yours.

[jvanick]

Wildcard... with how important good exposure is to the whole process, you should totally take Jay (homer) up on his offer.

For light sources, you want something that's strong in the 360nm (Pure Photopolymer) to 400nm (Diazo) range.  Most LED lights are typically single or narrow-spectrum light sources, so trying to get a good exposure out of them unless specificialy made to emit UV light won't work too well). 

MH grow lamps will definitely work better than FL tubes, if you can find something in the 1000w-3000w range, you'd be doing really good.

Remember to get an exposure calculator of some sort too, so you can optimize your exposure times after changing all these variables.

-J

[lrsbranding]

Getting bulbs with the right light spectrum is very important. Don't grab something off the store shelf and hope it works. Don't forget a single light source unit will be a lot deeper than a fluorescent unit so if your cramped on height it may not fit. Here are pic's of my evolved compression lid fluorescent exposure unit. Made a box to accommodate the larger glass. The neoprene sits between the lid frame and glass then wraps up the outside of frame so getting a good seal is no problem.  Used a motorcycle valve stem through the neoprene with the valve removed. Got an a/c evac. pump from Harbor Freight. The light source is a LED insert conversion from Vastex. Most important tip I found is after deciding how big of screen you want to make, be sure your glass and vacuum top is large enough to sit down around the screen frame and make contact by itself. Also the tightness of the neoprene will affect this. Other wise you will be standing there squeezing the frame to the glass to start the vacuum.

[andyandtobie]

Nice!  Would it be rude if I asked what the Vastex conversion piece cost?  We need to upgrade our exposure unit on a tight budget, so we're going to be building something soon.

[Wildcard]

Homer, thank you for the offer. I'm located on the Gold Coast, Australia, so it probably means that the shipping would end up a big hurdle (not sure where you are located or how well the unit will pack down onto a pallet).
@jvanick & @irsbranding, thanks for the additional advice and pics. Much appreciated.

[Homer]

no Problem - mate!-   

offer is open to anyone else looking to build a unit.

[andyandtobie]

Wow, if I could afford the freight, I'd be all over that.  Unfortunately, I'm in northern Idaho, on the other side of the country.  Argh.

[Wildcard]

Yeah I'm not even going to bother with looking into freight to Aus

[Wildcard]

I've done some looking into the metal halide grow lights and from what I can tell, these lamps require a few minutes to warm up to full output.

Do all MH units use a shutter for exposure rather than a basic on/off/timer switch? Not sure I'm keen on trying to build a DIY light shutter.

[Frog]

I've done some looking into the metal halide grow lights and from what I can tell, these lamps require a few minutes to warm up to full output.

Do all MH units use a shutter for exposure rather than a basic on/off/timer switch? Not sure I'm keen on trying to build a DIY light shutter.

Kinda' the nature of the beast

Just another area that LED's appear to offer an advantage.

[mimosatexas]

My diy shutter is a piece of sheet metal i move to start exposure.  I am also using a grow bulb.  Basically, I have lots of airflow across the light and the glass, and manually remove and replace the shutter.  It doesn't get hot and neither does the glass.  You can make the shutter hinged or have it slide back and force or just lift it off and set it to the side.  You don't need anything fancy and automated.

[Frog]

My diy shutter is a piece of sheet metal i move to start exposure.  I am also using a grow bulb.  Basically, I have lots of airflow across the light and the glass, and manually remove and replace the shutter.  It doesn't get hot and neither does the glass.  You can make the shutter hinged or have it slide back and force or just lift it off and set it to the side.  You don't need anything fancy and automated.

Although, a little ingenuity along with a solenoid and a spring can come up with at least an automated way to close it fairly easily.