Hi,
1. I believe I read someplace that you could program the unit to hit the switch and then back off the switch before stopping. How is that accomplished?
What you are referring to there is homing, and what you have described is not the norm with Mach3 and parallel port motion
controller but is enacted by certain specific motion controllers only.
Generally what happens when you 'home' your machine is that each axis in turn drives towards it's home switch. When the home
switch activates it stops and backs up until the switch deactivates, whereon it stops. The machine coordinates for that axis
are set to zero (or some other number called home offset, as programmed in the Homing/Limits page). Note that specifying
a non-zero offset does not cause the machine to drive to that location.
Some motion controllers, the PoKeys 57CNC for example, however allow you to specify a distance and the machine will drive
to that location. Machs parallel port motion controller does not have that feature.
To be honest its not such a big deal. Lets say you want to drive the x axis to a location 4 inches from the home
switch, which we will assume is at the end of the x axis travel, then you would specify a home offset in the Homing/Limits
page of -4 inch . When the x axis homed it would stop just after it had backed of the home switch. Once homing is
complete you issue an MDI:
G0 G53 X0
This causes the machine to drive to the x machine coordinate x=0, which is 4 inches from the home switch.
What a motion controller (that has the 'drive to offset' feature) does is automate it. You can do it in a two step
process with ordinary Mach and parallel port.
2. There is a ++, and --, but I assume the "home switch" refers to software switch? If I am correct, how is it programmed?
No, it is a real switch. Most people have, say, the X-- limit switch to double duty and be the X home switch also, but you
could have a separate switch if you wish. There are certain advantages in doing it that way but requires more input pins
than you probably have. Lets say you have the X-- switch assigned to port 1 pin 11 in Ports&Pins/InputSignals page.
You would assign the same pin to the X home signal as well, that is port 1 pin 11. Then when that pin goes active it
would be treated as a limit normally, but if the machine is homing then it would be treated as a home switch.
Craig