I have been reading through heaps of posts and it seems most people are mounting the fresnels between glass. I want to have as much light reaching the screen as possible so I want to forego the glass. How do you frame the fresnels without using glass so it doesnt end up bowing?
Any help apreciated.

I have the same problem, but I haven't found a good solution yet.

A ridgid frame would help keep it flat but I don't see a way to assure that it is absolutely flat without glass. It has been determined that when they bow, they bulge out from the middle toward the grooved side. So you should be able to use only one piece of glass on the grooved side with the edges captured in a frame. This will also help keep the grooves clean.

Of course you would still need the tempered glass/heat shield on the collumating fresnel, so that's three pieces of glass total.

Do both of the fresnels bow, or just the one that is closest to the lamp?

I also read somewhere that the fresnels bow because the slots they sit in are too tight, not allowing for any expansion. Is this correct? If this is the case, couldn't you just make the frames for the fresnels a little bit larger than they need to be?

I'm trying to figure this thing out too. I have my monitor stripped and am now in the box-design phase.

Generally just the one closest to the lamp. The front should not ever get hot enough to warp.

I have my fresnel slid into slots on either side rather loosely. It did bow inward slightly and I fixed that by placing a small piece of wood at the the base to keep the bottom from bowing. Then I cut a groove in a piece of wood and screwed this on the top of the fresnel. Now I have no bowing at all and I maximize light throughput

Would you be able to show a picture? so I can have a better idea of what you are describing.

Thanks.

I'll try and remember to hop up on the ladder and grab a couple shots for you later this evening ;-)

I tested using a 1mm thick, 15mm wide strip of galvanized steel (strap) as a cross brace, eg. for an X pattern. It cast an out-of-focus but still very unaccceptable image on the screen. Oh well.

My test setup was 330mm fresnels both sides, 330mm pj lens, 7mm arc 50W halogen lamp. New to my setup is a bulb with a fairly elliptical dichroic reflector ($6 at Walgreen's)... this reflector brightens the image very dramatically, compared to a bare 7mm halogen bulb of the same wattage.

I ended up using a strip of 10mm aluminium angle mounted along the top with high temp silicone sealant for the rear fresnel. no bowing or warping after many hours of PJ use. ( I don't have the rear fresnel mounted on the heat shield, I have a gap of 1" between the tempered glass and the fresnel, in hindsight I should have just mounted the heatshield closer to the LCD and mounted the fresnel on the tempered glass as in the plans, it would have been easier.
For the front fresnel, it isn't framed at all, I just Bluetacked it in place at the right angle for keystoning, glued a small piece of plastic channeling next to it on either side and hold it there with bluetack. works very well and was very easy to do. I don't need to adjust keystoning at all as the projector is permenantly mounted in a coffee table and will never be moved.

Wait, wait, wait .. you can't just throw that out without details!!

50W halogen??
Eliptical Reflector!!?? (Drool)

Pics please!!