My dad has a pretty good collection of scrap and devices he's bought on sale or at the thrift shop. He is a first rate scavenger. I came to visit my parents for a two week vacation. Looking at his collection I just knew I had to Make something.

After a quick look around I decided on one of the projects he would have certainly vetoed when I was a kid. A solar furnace built from the lens of an overhead projector.

Having recently been to a Maker Faire and greatly impressed with the open source building system called Grid Beam I decided to incorporate it into this project.

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Step 1: Gather Materials

You won't need much for this project and only one item is at all hard to find.

A sunny day. I found mine in Southern Colorado in June. 100F in the shade. Plenty of sun.
The Fresnel lens out of an overhead projector or back of an RV or other source.
Some wood. 4 to 6 feet of 1.5" or 2.0" square stock is ideal. (In reality mine was 1 2/8ths square)
A drill or drill press with a 5/8ths bit.
Six to Ten 1/4" carriage bolts and nuts. The bolts should be 1/4"-1/2" longer than twice the width of the square stock.
A socket or wrench for the bolts.
Some bricks are nice to have. Firebricks if you have them.

Step 2: Liberate the Lense

The one in this projector came right out. I didn't even need a screwdriver.

Step 3: Make the Grid Beam

Grid beam is square stock with two holes drilled at regular intervals that are the same distance apart as the width of the stock. One hole goes from top to bottom and the other side to side. The holes intersect each other.

You can snap a line down the center of the square stock and carefully measure the intervals. If you want to use your grid beam to make something nice like a book case or bed this is probably a good idea.

If you just want some sticks to mess around with, the system is pretty forgiving of sloppy carpentry. I just took a bit of stock and used it to measure off the intervals and then eyeballed the center line.

This step took me the most time of everything in the entire project. The sticks are adjustable and re-usable for other projects so it was time well spent.

Step 4: Frame in the Lense.

lay the lens down on some two of the sticks and pin it down with two more. Don't over tighten the nuts and crack your lens. I would have cut my small sticks a little longer, but some hings on the square stock had dictated my cuts.

I ended up centering the lense on the long sticks after some testing. That's the magic of Grid Beam, it took 30 seconds to try a new layout.