@ onetrack: But how did they make the 1st propellor perfectly, to enable it to be used as the master on the copy lathe?
A propellarblade is an array of wing-sections, differing in thickness and incline as the speed through air is higher at the end than close to the hub.
The cross section is rather easy to calculate for each 1/4" and likely ist possible to cut out the same sections in 1/4" wooden plate and stack them all together, whereafter the 'digital' surface is smoothened to 'analog state' with sandpaper!
Actually I think the RC-guys makes wings in the same manner, just with styrofoam :-/