An egg incubator emulates the conditions a mother bird provides to her eggs before they hatch, including the heat and humidity that an egg would receive under natural conditions. Your incubator has an advantage over a mother bird in that more eggs can be hatched in a shorter time. You can fit more eggs in an incubator than a mother bird would be able to roost upon.
Place the smaller cardboard box into the slightly larger cardboard box. Fill the gaps with newspaper to serve as insulation.
Cut out the panel of the boxes that has been matched to the size of your pane of glass. Do this for the larger box and the corresponding panel of the smaller box to create an insulated box into which you can easily place your eggs.
Cut a hole just large enough to fit through the porcelain socket. Make this hole high on one side of the box. If it is too low then some eggs will receive more heat than others and heat will not be as evenly distributed throughout the box. Make the fit as snug as possible so that heat does not escape.
Fill a pie tin with water and place it in the corner of your box. The water will ensure that the conditions do not become too dry.
Tape the thermometer in a place where it will be easily viewable and close to the area in which you will place the eggs. Maintain the temperature at the ideal heat for eggs to incubate, which is usually between 99 and 101 degrees Fahrenheit. If you are making a larger incubator, place another thermometer on the other side of the box to ensure that the heat is being evenly distributed
Tape the glass over the opening to secure it.
Plug in your light and test your incubator. Check to see if the heat stays consistent at the intended temperature. Heat can be adjusted by changing the wattage of the light bulb or the amount of insulation provided.
Add your eggs when the temperature is consistently maintained and regularly refill the pie tin with water as needed.