I was on a no-budget budget in high school. I had saved all my pennies to buy a nice 35mm camera, and had nothing left for the darkroom side of the photo equation. But I realized that the camera was a reverse enlarger, and the expensive parts of projection were already available to me on the camera.
So I made a structure in sort of an A-frame shape, about 5 ft tall, standing on the floor, with a small plywood platform on top, where I cut out a hole to fit the camera with the back open. I made a reflector housing from sheet aluminium and mounted a 60 watt, 120VAC bulb so that it would shine thru the back of the camera, thru the lens and vertically onto a horizontal plywood table where the photo paper would be.
I had to make a small, weighted glass piece to hold the film flat, since the camera back wasn’t pressing on the film. This helped dissipate the heat, which never seemed to be a problem.
Since the enlarger “head” could not be moved, I put shelf brackets down the inside of all 4 legs, and to change the enlargement ratio, slid out the table and moved it up or down to a new position.
I even made a 45 degree mirror block to project the image on the wall for extreme enlargements.
Since the camera had an advance mechanism, it was easy to move the film exactly one frame at a time with the lever.
One of the great things about the optical arrangement was that the image was projected back thru the same lens as was used for exposure, and this seemed to cancel out any distortions. The prints were amazingly sharp and clear, much better than real enlargers I had to use at school.
One of the cute things I did was to write a scale down one leg, measuring the distance from the film. Next I made a chart (using a slide rule!) of exposure times vs. distance. So if I had computed the exposure to be 10 seconds at X inches, I could change the distance to Y inches and know the correct exposure from the chart and not have to run test strips.
Yes, I know that could be done with a conventional enlarger, but I never saw it done before.
It worked, and I used my lumber enlarger all thru high school.