One easier trick for bevel gears: If you extend a line from the crowns (or roots) of the gear teeth, they’ll all meet in a single point called the “Apex”. The Apexes of two meshing bevel gears must be coincident. See below:
So in your 3D cad program, you can draw a sketch on the midplane of each of your gears to find the apex point. Then in the assembly, mate the two apex points together. Then measure to see how far off the rest of the assembly is
Good luck with the project! There isn’t a lot of need for differentials in FRC, but they do come up once in a while:
