Wheel construction
Outside edge of wheel has a "crown" to it.
Wheel is wider in the middle than at the rims.
Widest part of wheel should be 40 cm in dameter or slightly less. If you have a soft metal tape measure, check the circumference to be 125.6 cm.
Main wheel disk should be roughly 3.0 cm thick.
Use good quality plywood, but it doesn't have to be the fancy birch plywood.
Add flanges to bring the middle of the gear to about 4.2 cm in thikness.
1 3/8" or 4 cm holes, 11 cm from center. These holes are to make it easier to turn the wheel by hand. Also use them to put bar clamps through when gluing the flanges on.