Hi,
its common practice to wire all the limit switches in series with normally closed contacts. When any one switch operates the continuity of the switch string is broken and
that is what Mach detects. There again its common, but not universal to have Mach Estop on a limit event.
Large and powerful machines are even more safety oriented and a limit event will cause the axis drives and spindle to de-power. When a machine de-powers in such a manner
it is a time consuming matter to restart the machine, assuming no damage is done, and pick up where the job currently in the machine is and start from there.
None the less safety requires such an arrangement, if the controller has 'brain fade' and the EStop doesn't work or is slow, it is essential that the machine be made safe.
Because of the inconvenience and lost time a great deal of effort is expended to prevent a machine from ever operating the limit switches.
Mach has soft limits. They are programmed usually to be just inside the physical limits and limit switches. The program will detect that you or your Gcode is attempting
to drive your machine out of bounds and stop you. They work really well, but they absolutely rely on the machine being referenced or homed. So when you turn your
machine on and you 'home' your machine it will drive to pick up its home switches in each axis. Mach knows thereafter where it is in relation to the boundaries of the
machine and soft limits become useful.
It is for this reason that I argue that good, reliable, repeatable home switches are more important than limit switches. For about a year or so I operated my mill
without home switches and suffered a few crashes because soft limits didn't work because the machine was not repeatably referenced. Once I got around to fitting
home switches the number of out of bounds moves dropped dramatically. Good home switches were the best addition/development I ever did on my mill not to mention
very cheaply too!
Craig