you may use the reference planes to assemble the gears.
Just a simple example assuming that both are identical
and have been constructed on the x/y plane:
- place first gear
- place second gear:
- use Planar relationship
- show placements part's reference planes
- select x/z plane of placement part and
connect to x/z plane
(Y-axis movement constrained)
- use Mate relationship
- select x/y plane of placement part and
connect to y/z plane (use your calculated offset)
(should now be at 90 deg to 1st. gear)
- use Mate relationship
- select y/z plane of placement part and
connect to x/y plane (use your calculated offset)
(Z-axis movement constrained)