As described here*, I've set my Z upper limit switch to max/homing and
Z lower limit switch to min/disabled. Here are my settings:
$4tr=2.540 (mm travel per revolution)
$4mi=4 (microsteps, 1, 2, 4, 8)(default)
$4po=1 (0=normal,1=REVERSE)(default)
$zsn=0 (low, min z switch, 0=off)(default)
$zsx=1 (high, max z switch, 1=homing)(default)
$ztn=-95.000 (travel minimum)
$ztm=0.000 (travel maximum)
G28.2 Z0 homes exactly as expected: It moves UP...in the POSITIVE direction...toward zero :-)
However, I'm wanting to locate the top surface of material to be cut and find notes on "Automatic Z Homing When Milling PCBs"***
The hookup makes sense but indicates that the result of issuing G28.2 Z0 (same as above) "will move the Z axis in the NEGATIVE direction."
How is this possible?
So I'll answer my own question in case it's helpfull to some other CNC nube.
With the settings below I have (for my machine) both G28.2 and G38.2 commands working as they should. :-)
"G28.2z0" homes to my upper/max switch.
Making no software setting changes, "g38.2 z-100 f1000" moves down to my alligator clip and touch plate (a Normally Open switch/sensor) that is connected to the TinyG Zmin and ground terminals.
settings for my machine:
(motor 4/Z, direct drive 1.8 degree, nema23, 2.8amp, 269 oz.in.)
$4ma=2 (map to axis, 0=X,1=Y,2=Z)
$4tr=2.540 (mm travel per revolution, 2.540)
(1/2 dia., 10 tpi ACME right-hand lead screw)
$4mi=4 (microsteps, 1,2,4,8)
$4po=1 (polarity, 0=normal,1=reverse)
$4pm=3 (power management)
It's always good to keep in mind that up/down, left/right, positive/negative, max/min etc are relative to polarity setting, which is influenced by how you connect your stepper motors to tinyG. Here is a reference
Stepper wiring varieties result in a varieties of setups.
Setup step #1 is always, for your type of motot, to get it connected to tinyG so that tinyG, on command, can spin the motor ClockWise (CW) and CounterClockwise (CCW). Then depending on your machine, when a motor is installed on an axis, CW may be up, or may be down. you can reverse the "up movement" by either changing the motor polarity setting or by rewirng the motor leads connected to tinyG.
Summary - what works perfectly for mristau with $4po=1 might require $4po=0 on another machine , depending on the wiring.
This topic is from the original forum (February 2015). Your reply starts a new discussion linked to it.