Here is a link I saved some time ago.
https://www.backyardchickens.com/th...w-we-did-it-and-test-run-ready-set-go.861788/
It looks like a good start. I would look to use a different material than wood inside the incubator. Maybe wood is ok, but humidity and wood might not be a good combo long term.
I made a small incubator a couple of years ago and got pretty good hatching rates on quail.
Heat shield is metal lid from a bent lunchbox. Lightbulb was 25 watt, I think, ceramic socket. Attached to a dimmer - outside of the incubator. Piece of wood to support the egg trays. 2 layers of plexiglass - one layer caused condensation, so two seemed necessary and no more condensation after the two layers installed.
To vary humidity, it worked well to have holes in the water filled glass and then move it above the light, or away from the light as needed for more or less humidity.
Change I would make: put the lightbulb closer to the bottom of the cooler. it is a still air incubator, so more airflow would have occurred with heating the cooler air that sank, causing it to rise better and create more of a thermal flow. If you can see, the HWC is raised up off the bottom, but flat, then vertical, then a horizontal shelf where I put the water and protected the lightbulb from any thing hitting it.
I rotated eggs 3x per day. I took the 2 layers out, put bottom on top, then turned the whole thing 180 degrees and put it back in. Generally, using paper trays isn't a great idea, but it seemed to work out ok. Should also note that I sat this whole thing inside a larger-than-the-incuabator (but not taller) cardboard box to try to help mitigate temp fluctuations. Seemed to help.
Cost: Styrofoam cooler bought at store ($5?), light bulbs to test out for temp, dimmer. Everything else we already had.
Good Luck and Happy Mother's Day!
