When you request referencing (by button or GCode) the axis (or axes) that have Home switches
defined will travel (at a selectable low speed) in the defined direction until the Home switch operates.
The axis will then move back in the other direction so as to be off the switch. During referencing, the
limits do not apply.
When you have referenced an axis, then zero or some other value, which is set in the Home Off(set)
column of the Config>Homing/Limits dialog, can be loaded into the axis DRO as its absolute
machine coordinate. If you use zero, then the Home switch position is also the machine zero position
of the axis. If the reference goes in the negative direction of an axis (usual for X and Y), then you
Table-X+XFrame-X andReferenceramp+X, X & Ref switch-+X ramp
4-15
might get referencing to load something like -0.5” into the DRO. This means that the Home is half an
inch clear of the limit. This wastes a bit of the axis travel but if you overshoot, when jogging to Home,
you will not accidentally trip the limits. See also Software Limits as another way of solving this problem.
If you ask Mach3 to reference before you jog off the switch, then it will travel in the opposite direction
from its “reference” direction (because the machine already on the Home switch) and stop when the
machine gets off the switch. This is fine when you have a separate Home switch or are on the Limit at
the reference end of the axis. If, however, you are on the other Limit switch (and Mach3 cannot know
this, if the switches are shared), then the axis will move away from the actual Home point until it
crashes. So the advice is always jog carefully off the Limit switches, then reference. If you are concerned
about this problem, it is possible to configure Mach3 so it will not automatically jog off the
home switch.
From the manual Mach3Mill_Installation and configuration...
Bill C.