This is a plain and completely parametric model of involute gears. It's meant to serve as a base for further gear customization.
To modify it, go to Tools > Parameters.. from there, you can change the parameters' values:
Pd - Pitch Diameter
Phi - Pressure Angle
k1 - Addendum Ratio (a = k1/Pd)
k2 - Deddendum Ratio (d = k2/Pd)
N - Number of Teeth
Thickness - Disk Thickness
I've included two slightly different models. One works when Rd > Rb and the other when Rd < Rb. If the model throws an error with the parameters you've set, then switch to the other model.
Rd = N/(2*Pd) - k2/Pd
Rb = [N/(2*Pd)]*cos(Phi)