Axis Viewpoint

[Gene Warren <gwarren-at-execpc.com>]

Hi Enrique,

Enrique Sanchez Vela wrote:

---- stuff snipped o< ------

>
>   Also I have a CNC question, when I jog or mdi the table to the left,
> the value on the X encoder decreases, is this correct or do I have the
> encoder wired backwards?
>
>   also, where is home supposed to be?
>   moving the table all the way to the left and all the way in?
> thanks,
> esv.
>

     According to EIA RS-267-A, "Axis And Motion Nomenclature For
Numerically Controlled Machines", June 1967, Positive X axis is "to the
right looking from the spindle toward the workpiece".  Positive Y is "in
the direction to make a right-handed set of coordinates; i.e., +X rotated
into +Y advances a right-handed screw in the +Z direction".  Positive Z is
"in the direction from the workholding means toward the tool-holding
means".

     "The location of the origin (x=0, y=0, z=0) of the standard
coordinate system ..... may be fixed or adjustable."

     That's also as clear as mud.  Your Tree Mill is Homed when the Y axis
is all the way towards the column, and when the X axis is all the way to
the right.  Tree Mill specs, not mine.

     Once you get the Machine home, a positive voltage from the
Servo-To-Go to the X axis drive (your Gettys pin No. J7-2, wire no. 418,
red) should send the X axis towards the left and the encoder counts should
increase.  A positive voltage from the Servo-To-Go to the Y axis (Gettys
J7-4, wire no. 428, red) should send the Y axis away from the column
towards the operator, and the Y encoder counts should increase.

=============================================================

    Back to the EIA RS-267-A stuff.  It's a matter of viewpoint.  Their
viewpoint is the tool moving.  The tool on your mill does not, of course,
move.  The table moves.  Sending the table left, as I have indicated, is
the equivalent to sending the tool to the right, and you meet the EIA
specs, as Tree Mill did.

    That screwy Y Axis is a little more difficult to explain.  If you  put
a piece of wood on the table with a wood screw sticking up and push the
right side of the table away from you, you screw the wood screw into the
spindle (right-handed screw going into the +Z direction) and meet EIA
specs.  It's the best I can do.

    It's a real brain buster, but:  +Y is towards the column.  (Table
moving out = tool moving back)
+X is to the right.  (Table moving left = tool moving right.)
+Z is up.  Easy one. (Tool moving away from the workpiece)

My head hurts.

     For Drilling purposes, you have a computer controlled positioner and
a manual (Armstrong) drill, just like a drillpress.  The Tree Mill has no
computer controlled Z Axis.  (If you did, the Z Axis going down would make
encoder counts in the minus direction.)

    The origin (Program Home) is where you set it.  Some people want to
set the Program Home so they can program all positive moves.  Others want
to set the Program Home to the center of the Spindle.  You set that in the
EMC somewhere.  The main thing to consider when you program is to think of
the tool moving and set your machine axis to act accordingly.

Later,
Gene