Re: Going home

> Why not make the home switch adjustable like it is on my mill?
> Smoke

Smoke, List,

Depending on your use of the machine, this can be a bad thing... Home
is a REFERENCE position, from which ALL other coordinates (on the
axis) are determined...

If your home is adjustable, how do you "go back" to something you set
up last week? Without setting it up again? A fixed home position
allows for this possibility. A movable home position will also shift
ALL your fixture offsets(G54-59) as well!

You could use a mechanical "extension" or "actuator" (or even a
second switch connected in parallel,or series; depends on wiring) to
cause the home switch to APPEAR to be somewhere else. But keep the
home position fixed, for the easiest usage by the operator over time.

Ian,

The switch need only be checked (in a properly operating machine
design) once, when the machine is first turned on. Control software
will often let the "resting position" to be specified as some OFFSET
FROM the home position. This lets you put the machines' "absolute
reference point" at any arbitrary position, as needed by your machine
or parts...

Some controls also have a "tool change" position, yet another
specified place in the machine travel that you cvan return to
reliably. Again, with a properly designed and functioning machine!
The HOME position is generally located at the extreme "corner" of the
machine travel. I've posted previously, and extensively on this
subject...

Finally, you have a "reference" or "release" plane (see R word in
Gcode, also G98,G99), which can be set at some arbitrary height above
the material surface. THIS is the point (in Z) that tools will return
to during a toolpath execution. It has typically been set .100 above
the part surface. More precise machines and pressing commercial
deadlines have some shops setting this plane much nearer the part
surface (to save transit time, as you suggest)

So put the Home switch at the top of mill Z (and W) axis travel, and
use the rich set of g code to deal with the other "points" you'd like
to return to...

Hope this helps.

Ballendo

P.S. On some commercial CNC Vertical machining centers, the z home is
set NEAR, but not AT the top of axis travel. On these machines a
positive Z move will be toward the TOOL CHANGER. Having this
distinction can make machine tool change "crashes" less likely, since
tool change takes place OUTSIDE the machine "working" envelope.

>>This may sound like a silly question but where on the 'Z' axis
>>would one normally put a 'Home' switch?
>>I assume it would be safest to put the switch at the top of the
>>axis, as far away from the table as possible but, if I then have to
>>home all the axes before starting a job, this could add quite a bit
>>to the processing time. My other thought would be to put the home
>>about half way up as the chances are that most machining will take
>>place near the bottom of the 'Z' travel. What do you think and
>>where is the home switch on your mill?
>>Ian??