Re: Linux vs. DOS

Tim Goldstein wrote:

> From: "Tim Goldstein" <timg@...>
>
> I hooked up my home switches for the lathe and tried the function out. Over
> all it works just as Jon described. HOMING_POLARITY controls the direction
> the axis moves when you hit the home button and HOME_SWITCH_POLARITY takes
> care of whether you switches are NO or NC.
>
> I found that if you set the HOME_SWITCH_POLARITY wrong what happens is the
> program functions just like it does with no home switches attached. Click
> home and it zeros out the selected axis without any table movement.
>
> The one thing I am disappointed in the home function is that the position of
> the switch seems to always correspond to 0.00 for the axis. In looking real
> quickly I didn't see a way to indicate home as being a different position.

It really doesn't matter. this is the ABSOLUTE position. You generally
never work in absolute positions, except maybe when calibrating permanent
fixtures onto the machine. Normally, you work in relative coordinates, ie.
relative to some edge of the part. So, you put an edge finder in the spindle,
and jog the part over until it deflects the edge finder. let's say we're doing
the X axis, and the part is to the right of the spindle, and we have a .2"
diameter edge finder. So, when it deflects, we enter by MDI, G92 X0.1
This sets the relative coordinate offset such that the relative coordinate
system is aligned with the left edge of the part. (The X0.1 is to compensate
for the radius of the .2" end of the edge finder.)
You can now do this with the mouse (I think it's a right click over the axis
in question, and you get a little menu.)
There is also the G10 L2 Pn X1.23 Y4.56 command, which sets up
to 9 work coordinate offsets from the main relative coordinates. Very
handy if you have multiple parts mounted in a fixture.

> >From my limited home shop type experience this is a MAJOR pain for setting
> up a switch for the Y axis (X in lathe terms) of a lathe.

So, the only time you should see absolute coordinates is after powering
up, and before initializing anything. (You can use it later to check for
lost steps, by re-homing.) The relative offsets from the absolute home
position are stored on graceful shutdowns, so you could come back the
next day and power up, home and switch to the relative coords, and you'd
be right at the same place. (The G10 L2 work coord offsets are saved,
too.)

The # key (I think) switches the display between relative and absolute.
The @ key switches between commanded position and actual position.
I keep it in commanded because the flickering digits are distracting.

Jon