Re: [CAD_CAM_EDM_DRO] New question about limit and home switches

> If I understand correctly, you are asking what happens if you drive
> over a home switch while running a program, subsequent to homing
> the machine. The answer is nothing - the home switch only gets
> looked at during homing. Running over a limit switch on the other
> hand will shut the machine down.

I'm not sure I understand the need for them in CNC. On the mill I used in
school we have a cursor keypad on the control to position the spindle
somewhere over where we want to consider home. Then you lower it until it's
pressing against the bit of plassy you want to cut into a shape and press
the okay key, setting this position as the home. Start the commands going
out, lots of most definitly cool whirling noises later you have a shape. I
can see the need for them if say, you were using a power feed so you don't
wack the table into the end of the travel but that's a limit switch isn't
it. Why do you need home switches if you can tell the mill where you want it
to home to when you start it? Would be it for things like, if the power was
turned off and you left the work clamped in exactly the same place you could
turn the mill on the next day, ask it to find home again and it'd set it's
home to exactly the same place as it was at the day before? Because if you
set it only as a position in the computers memory it's taking it as a
position such and such increments away from where the motors have the table,
which won't be remembered the next day. Or is it possible save the table's
position, motor increments from home, in the control so you can turn it off
and then ask it to use a set home position in relation to the saved table
position? I always thought the idea of CNC was that the machine knew where
it's own motors were going in relation to table size etc while it's running,
so that's how I've come to the perhaps completely mad ideas above.

John H.