I built my incubator by following Miss Prissy's 'Chic Chick Bator' instructions. https://www.backyardchickens.com/forum/viewtopic.php?id=8510 I added a small hatch on the side for easy turning of eggs without letting all the heat out. Worked pretty good 
I hatched my first batch of eggs. On day 18 I had 25 eggs and 20 of them hatched just great! 
I hatched my first batch of eggs. On day 18 I had 25 eggs and 20 of them hatched just great! Here's my bator....
Computer fan, thermometer, digital thermometer/hydrometer, water heater thermostat. I covered them with hardware cloth
after one chick stuck his wing in the fan and one got too close to the posts on the thermostat. Both are fine
And my wiring diagram
With eggs.... I put them in cartons on day 18 (numbers show order of hatch)
One of my clear eggs when I candled.. I ended up with about 5 or so of these...
My first pips.... They're a bit hard to see
Some hatching babies......
A few days old....
Computer fan, thermometer, digital thermometer/hydrometer, water heater thermostat. I covered them with hardware cloth
after one chick stuck his wing in the fan and one got too close to the posts on the thermostat. Both are fine
And my wiring diagram
With eggs.... I put them in cartons on day 18 (numbers show order of hatch)
One of my clear eggs when I candled.. I ended up with about 5 or so of these...
My first pips.... They're a bit hard to see
Some hatching babies......
A few days old....
