Vacuum Frame Tune-up

[ZooCity]

I split this off from the blanket thread so as not to clutter it up. 

We have a:

Millington Machine Co.
Model: VFDF180
Serial:  21225
appx. 66x54

I've never had a real vacuum pump to maintain so could use some pointers there. 

Glass- Millington recommended 1/4" tempered.  Sounds thin right?  I was thinking 3/8".  My understanding is that tempered glass is not good for exposures but I don't see how you could use anything but on a large unit like this.

The rest of it is fairly simple it seems.  We don't use a rope on our homebrew expo unit which has the double cloth faced neoprene (which has lasted, unprotected and using roller frames for I think 5 years now) and draws it's air via ports on the sides of the 1x1s that comprise the lid frame.  It looks like these professional frames use a tube that draws air which is different for me. 

We got the big unit to do big frames and, hopefully, 2 of the 25x30s at once but I wonder if the draw down isn't much slower on a unit like this.  Our homebrew unit draws and releases really quickly and our expos are in the 11-18 ltu range with each ltu appx = to a second so it let's you really move. It also keeps the light contained which is nice. 

fwiw, I did check out the reflector type on our Olec to ensure proper distance from glass to glass and what not. 

[ScreenFoo]

Thicker glass=longer exposures.  Not that it sounds like a problem for you. 

What kind of pump do you have, a diaphragm or rotary vane?  A bigger pump won't take long to draw down a bigger frame...  although if you're used to a shop vac, the CFM will be quite a bit different.

[ebscreen]

Big frames like that usually have big vacuum pumps which usually get the job done pretty quick.

As for the glass, I know other swill swear that you must use photo glass, but when I broke the
glass on my Douthitt (it's like 4x6' or something. Don't ask.) my glass dude wouldn't let me have anything
other than tempered. No complaints, shot beautiful halftones.

[ZooCity]

Big frames like that usually have big vacuum pumps which usually get the job done pretty quick.

As for the glass, I know other swill swear that you must use photo glass, but when I broke the
glass on my Douthitt (it's like 4x6' or something. Don't ask.) my glass dude wouldn't let me have anything
other than tempered. No complaints, shot beautiful halftones.

I heard the same, that tempered was a no-no and have always used much thicker, un-tempered 'float' glass on our unit.  My theory is that the tempered is bad for exposure but you can use much thinner glass so it's not losing as much UV as it travels through, probably works out even stevens compared to regular float or optically clear (starfire I believe). 

There was a bad ass thread back on the old tspmb boards about this I think.