I'm having trouble locating 1/8 in tempered glass at what I consider is a reasonable cost. The local glass suppliers want about 30 dollars for a 14" by 10" piece. My local Home Depot has lexan much cheaper. I'm building a verticle enclosure and will be laying the collimating fresnel on top of whatever I use. The 1/8" thick lexan felt to flexible and I'm afraid it might sag. They had thicker plastic that was stiffer but it was not called lexan. Has anybody used any plastic other than lexan with success? I don't think 1/4 stock should reduce tranparency that much, but I'm not sure if plastic is as clear as glass in the first place. Am I splitting hairs too fine on this? Should I just bite the bullet and fork over the 30 bucks? Should I just go away and stop asking these dumb newbie questions? (Not much chance of that as I'm still only in the procurement and design phase.)Opinions on any and all of these questions would be greatly appreciated.

Schoolman:

I'm using 2 barriers right now.

1 piece of lexan (up near my rear fresnel) and one small about 5x7 piece of glass from a halogen floodlamp near the eye.

The reason I'm using 2 is that I find it is helping me keep my lcd temperature chamber where I want it to be. I did lots of experimenting with the lexan and halogen glass. - positioning, doubling it, gaps, etc.

I tried doubling the 1/8" lexan. I found it didn't block any more heat than one piece. Also, I couldn't notice any light decrease with the 2 pieces (or 3 pieces for that matter).

The only thing I found with the lexan is that it it's really close to the lamp (around 4-5 inches) and I checked it after about an hour, it's very warm to the touch, and it tends to be somewhat bendable (flappy) if you push it by hand when it gets hot. Seems like it works ok for me. Also, when I cut it with the table saw, it cut nice and clean (I gues since it can take the heat).. Regular Plexiglass has a tendancy to "Melt" when you try to cut it.

From what I can tell, the lexan seems to be as good as the tempered glass. I think someone else mentioned that in a previous post also... They switched from lexan to tempered for around $30 also, and figured they'd get a temperature decrease in the lcd chamber but they concluded it worked no better.

On a side note, I was going to encase my fresnels in glass to protect them from dust. Seemed to be a big deal in the forums. But during my projector construction, I had a few mishaps where my fresnels got full of dust and even dropped one between a piece of a plywood and a rough concrete wall. The fresnel got all scratched up. Both fresnels look rough and full of dust, and I can honestly say I can't see any problems in the projection, so I think the handling/dust concerns of the fresnels are a little overrated.

the_big_show

Thanks for the benefit of your experience Big Show. I think I'll try the lexan first and see how it goes.

what about 2 lexan sheets that sandwhich the LCD in side to protect it from dust? 7 Is this needed, or is it overKill?
Also, how far should the Lexan be from the light, and how far from the first fiesnel then?
I appreciate all the help. Thanks!

Hi to all.

My last experience with Lexan (15 years ago...) proved that it was very resistand, almost impossible to break.

I also remember one thing though... it would easily scratch. Has this changed or does have the same problem ?

Thanks

CBY

Nope has not changed, still very soft material and easy to scratch.

Hi


I'm having trouble finding Lexan in Norway. Anyone who have any good sources for it?

Anyway, the one I could find is 3 mm thick and a sheet of around 250 x 350 mm would cost around $35. This one can take a temperature of 140°c (284°F). Does this sound like the right stuff?? The same shop can sell me normal tempered glass at around the same price..

Have anyone measured the temp on the bulb side of the tempered glass??

The Edge

"Lexan" is a trademark. Look for polycarbonate.

A common use for the material is as replacement windows in doors, to make it virtually impossible to break the window and open the door from the inside.

Ok, thanks alot. This will help, as I have seen polycarbonate several places..

The Edge