Yes it is a bit backwards.
You need have AXIS_Z MAX LIMIT and JOINT_3 MAX_LIMIT the same 70? (or 100)?
set the following JOINT_3 paramaters:
STEP_SCALE = -200.0 (negative will reverse the motor direction so it is correct)
HOME = 65 (or 95)
HOME_OFFSET = (72 or 102)
HOME_SEARCH_VEL = 20.000000
HOME_LATCH_VEL = 1.000000
HOME_FINAL_VEL = 10.000000
EDIT: Here is a diagram of a Z axis (we should add it to the PlasmaC docs):
linuxcnc.org/docs/devel/html/plasma/qtpl...tml#qt_initial-setup
Thats quite a good diagram, thanks for adding it to the docs.