Hi,
welcome aboard. The confusion over these terms is very common when starting out and can still catch you out years down the track.
A large part of CNCing is understanding these terms and being able to use them sensibly.
You may have noticed with Mach4 enabled on the file ops tab there is a button 'Help Docs?'. On that button you'll find a directory of useful
manuals and reference documents. Over a period of time you will probably find several other useful documents and they can be added to this
list, I have some for ENUMs and pound variables and more for LUA coding.
This one is useful
Mach4 CNC Controller
Mill Operations Guide
If your new to CNC then
CNC Programming Handbook by Peter Smid
is pretty much the bible for CNC.
The upshot is that when you turn a machine on the machine has no idea of 'where it is' unless you have some very expensive absolute linear encoders,
and if you had those 'why piss about' with Mach4 when you can afford Fanuc/Seimens? Consequently you need to home or reference your machine.
Its common to use one extreme corner of the machining envelop as reference but is not in fact required. The simplest way to achieve that is to fit
microswitches, one to each axis, called home switches. When you home or reference your machine you will drive an axis until it triggers its home
switch, back up a little until it deactivates again, and set its 'machine co-ordinate' for that axis to zero. The next axis in the list will now be homed
in the same way. When all axes are homed the machine knows where it is and will maintain that knowledge throughout the session. It will know
for instance that its getting to very close to the end of travel on an axis and will fault out if you try to exceed the travel limit if you've set soft limits
correctly.
Most users fit limit switches as well, one at each end of an axis. If the machine tries to drive off the end of an axis it will trigger a limit switch and
go into emergency shutdown. Emergency shutdowns will often mean that the machine loses an accurate measure of its location and so restarting
the machine to continue with the job clamped in the vice may be out of whack and wreck the part. For this reason we try to avoid banging into the limits
whereas soft limits can be used and the machine can shut down and protect itself in a controlled manner and so that much easier to restart the
job if required.
Soft limits only work if the machine is referenced, its no good telling the machine 'don't go beyond 1000mm' if the machine doesn't know where it
started from. You can program Mach to know what the extents of your machine are, very useful. It will also warn you if the part program you've
just loaded exceeds your machine boundaries.
There are a number of techniques and tricks that can be used to reduce the number of switches and wiring by combining some functions together.
They can be confusing if your just starting out, I would recommend separate home switches but all six limit switches can be linked in series. While
even more comprehensive arrangements can be devised this one is reasonably simple to implement and understand and still offer good results if
soft limits are used intelligently.
Craig