Exposure Unit Glass just cracked/exploded [&$#@#*&!&]

[mimosatexas]

Welp...guess it's time to finish my metal halide unit :/

Looks like I can get a new piece of standard glass for $45 by tomorrow morning, but I'm definitely going to finish the vacuum unit ASAP.

[Doug S]

That kind of stuff never happens at a good time.

[mimosatexas]

Yea I have two rush jobs due by end of day tomorrow, and about 600 more shirts across a few others due by the end of the week :/  I'm cleaning the crap out of my shop in the interim though

[Homer]

I have the perfect set up for you....I have a Douthitt DMA that won't fire up... but it's a solid unit, you can stick that MH ballast right inside and boom -done....vacuum top is in great shape, glass too....remove the guts and you'll be set to go. It has an integrator in it too...let me know...

[ABuffington]

When ordering glass for an exposure unit it is important to request optically clear glass.  Commercial glass, especially for windows, has a UV blocker in it, which kind of defeats the purpose it is used for.  Also ordering optically clear in safety glass prevents a worker from a major accident.  We had a free standing vacuum frame on a mezzanine once.  When it was being raised for an exposure the worker lost his grip and the table slammed up against the stop.  We had bought it used and didn't realize it had plate glass, not safety glass.  When it broke, 2'x3' chunks fell to floor below and missed a worker by inches.  Safety glass can be optically clear.  Make sure to get the same thickness.  The Douthitt offer looks pretty good to me!

[sben763]

Star fire glass.  They make it in plate and safety glass. My 33"x47" cost $142 with tax. For the plate glass

[T Shirt Farmer]

Star fire glass. 

StarFire or another Low Iron glass is optimal

[mimosatexas]

I got quotes for standard unfiltered clear glass, tempered and not, and starfire.  The only one that could be done overnight was standard untempered so I kind of had to go that route for now.  I called around to about a dozen shops and the least expensive piece of starfire in 1/4 for 36x42, which just happens to be the most convenient size for a rush replacement, was almost triple what you just quoted sben, and was going to take 7 days.  Not sure what source you got yours from, but that is absurdly under market based on what i saw both online and what local glass people quoted.

Thanks for the offer Homer, but I'm not in the position to pay what that unit is worth plus shipping costs right away.  I'll keep it in mind for a few weeks from now though for sure!

[Evo]

Make sure to run a step wedge test with the new glass. If the glass has lead and/or iron it can seriously filter the UV energy. You'll see your exposure times jump.

[sben763]

I just went our local glass company and was given a standard contractor rate which was only $20 less then the full retail.  Sounds like you area glass companies are high priced. The other glass company in our town told me around $200. The star fire is cut at the supplier and not the glass company so they don't stock it

[gtmfg]

The last time I bought Starfire I only paid $50 from a place in Minneapolis

[mimosatexas]

I'm not sure what the deal is...I called local and chain places on both ends of town.  The prices quoted were all almost identical and all were almost $30 per sq ft.  You seem to have gotten it for $10.77 per sq ft...which is less than some places quoted normal safety glass.

UPDATE: Just finished burning my first job on my diy metal halide with vacuum top.  I have to say I learned a hell of a lot during the process!  I'll post a thread in the DIY section when I have a free second, and after I finish the cosmetic stuff and make a few modifications, but so far I can say the following:

1. pond liner is garbage as a blanket, but it does the job.  I am going to buy a neoprene blanket asap to replace it.
2. stouffer testing is awesome.  I was able to dial in the exposure after two total test screens.
3. metal halide = woah!  GREAT detail and I'm exposing to a solid 7 on the scale in 65 seconds.  I'll likely do more testing for different coatings and meshes and adjust a few things with the height of the light and what not, but it is much faster and no undercutting!  I'm holding a 2 pixel line on a 300 dpi transparency, which just wasnt possible on my tube setup, and the screen has no scumming or tac on the squeegee side.  I even wiped it down with a paper towel to check for any discoloration, and nothing.
4. I'm using an oil vacuum pump from harbor freight, and I am definitely thinking a gast pump would have been better, though twice as expensive.
5. definitely need some kind of release valve for the vacuum.  It is lifting the glass when I try to lift the lid, so I am using a strip of koozie as a shitty quick release under one edge at the moment.  It works, but it isn't very elegant.

In hindsight, after really getting into this project, I can say that a fully functional used unit for $500-800 would almost definitely be worth it instead of building it DIY style.  I always enjoy building stuff, but there are a fair amount of specialized parts to a build like this that make the build cost nearly that much to do it right.  I only have about $220 in this version and mostly just needed it up and running asap, so I was limited to locally available stuff instead of online stuff or things like the starfire with lead times.  Adding better glass, a better blanket, and a better pump would definitely bump it up into the $500-$600 range.