Cardboard box construction

[yoyoman]

My goal is to produce a lightweight projector, and I was wondering if this might work. I am using a 15" LCD, so I'm automatically going to be heavier than a 7" design.

I have a cardboard box from my old computer, and it's pretty thick and sturdy. It's got a double layer of corrugated cardboard and an outside shiny layer, so all together it's pretty thick and not very bendable. I was thinking of mounting items on some sort of "track" on the bottom, or at least to build any wood items on the bottom. To keep it from burning, I was going to add some aluminum flashing around the area behind the first fresnel.

I was also thinking of mounting the projection lens on a sliding track using a pair of tracks from a ball bearing drawer glide (http://www.lowes.com/lkn?action=prod...012-130-1129WP). With that, i was thinking of "shrouding" the front area of the box with blackout cloth wrapped around a spiral wire frame, kind of like an accordian. With this contraption, I could "retract" the front lens when transporting it. By not using any wood for the front half, I assume that I'd cut the weight in half. Heck, would it even be possible to skip most of the majority of the frame and encase it all in the cloth/wire frame, like in a barrel shape. It might even look rather artsy this way ....

So, is this a hair brained scheme, or do y'all think it might work with more thought?

[Inkog]

"So, is this a hair brained scheme?"

Yep, unless your out for some insurance money

Jokes aside, this would be very dangerous.

[yoyoman]

Well, in retrospect, not enclosing the area around the lightbox was a dumb suggestion and would be very dangerous.

As for the front side, wouldn't shrouding it with cloth be similar to the recommendations given for OHP/LCD users to reduce light leakage?

[Stocker]

If all you are after is light weight, try fiberglass or carbon fiber construction. Possibly Nomex around the light engine!

You can have ANY shape you want with these materials.

[phillip0101]

sound like a bad idea to me! lol.... very bad.

If your using a 15" monitor its gonne be pretty big anyway, why would you need it to be light weight? your not gonna be moving it around that much if its that big are you?

[yoyoman]

After my first ballast arrived, and it was a brick, I decided I wanted to go the lightweight route, for convenience. I got a good deal locally on a 250w electronic ballast, so I've already reduced a great percentage of the total weight. I know the 15" will never be shoebox sized, but I have hopes that it will at least be portable.

Faites777's design at OMega-567s projector is pretty intriguing. I saw another design on some other site which showed the projection lense mounted on wooden dowels that could slide back into the box.

[ringram]

hmmmm, lets see....

Take a very hot light bulb, and enclose it with cardboard and cloth. Nope. I don't see any problem with that.

[yoyoman]

Wouldn't the aluminum flashing I mentioned + a cooling fan be sufficient to keep the heat down? I am also considering building the light + reflector into a small aluminum box.

[karrock]

Yes! Very dangerous to use cardboard!

I've used it for prototyping, as a light shroud/shield when I was gauging distances for the light path, but even very short periods of time, the heat of the lamp would noticibly discolor or scorch the inside of the cardboard box.

I've seen some projectors made with a lightweight aluminum frame and like the others have suggested, you could enclose it with a more fire-resistant paneling material like aluminum, fiberglass, carbon fiber or even lexan, with proper heat shields and cooling.

[Guy Grotke]

Aluminum or other shiney metal materials do not transfer radiant energy as well as materials with matte or black surfaces. This makes people think that they can use it as surface heat sheilding by mounting it directly on some material that would be damaged by proximity to the projector lamp. Initially, the reflective effect will keep the material cooler, but this ignores the heat buildup problem: The lamp will supply a constant source of energy into the metal, which has no way to dump that energy. The wood (or in this case cardboard) acts as an insulator for the metal. So the metal will get hotter and hotter, until it begins to scorch or even ignite the underlying wood or cardboard! This has been observed in real DIY projectors with aluminum flashing mounted several inches from the lamp directly on the surface of MDF.

You can (and should) use aluminum as a heat sheild around your lamp, but it can't be in direct contact with anything flammable. As long as there is forced air circulation over the surfaces of that aluminum, it can dissipate energy into the air. Transforming unwanted radiant energy into hot air easily removed by a fan is a great way to minimize LCD cooling problems.