torch height control problem

[drieslaas]

I'm having trouble setting up the torch height contro on our new plasma table.

Allow me to describe verbosely my understanding of the process:

I built a touch-probe which has the torch floating in a housing so that the tip can be touched on the workpiece. The z-axis is supposed to continue down for a known distance until a limit switch is tripped.

Z zero is reset, z is retracted by the known distance, z zero is reset again.

z is now retracted to the pierce height and reset again. The torch is fired and after a dwell, z is retracted to the cut height and reset again.

Now the code for actually cutting the profile is released and the torch height is managed.

So far so good.

I now have to figure the block of g-code that will achieve the above:

I suppose it will look something like:

G0 z20. (retract to above the workpiece)
G28.1 z- (probes for the limitswitch activation in z negative direction)
G92 z0.
G0 Z20. ( WHERE 20 IS THE KNOWN DISTANCE TO TRIP THE LIMIT ONCE THE TIP HAS TOUCHED THE WORKPIECE)
G92 Z0.
G0 Z3. (MOVE TO PIERCE HEIGHT)
G92 Z0.
M3 (SPINDLE ON TO FIRE TORCH)
G4 P2. (DWELL FOR 2 SECONDS AFETR TORCH FIRES)
G0 Z 2. (LIFTS TORCH 2MM TO CUTTING HEIGHT)
G92 Z0. (RESET Z ZERO )
.....CONTINUE TO REST OF PROFILE CUTTING MOVEMENTS

Can someone please have a look and see where the mistakes are?
I am sucking substantial parts of this from my thumb.

The Mach 3 setup reads the limit switch as z-home, by the way.

Thanks in advance

[I Lean]

Here's a little segment of a Gcode file I used recently, just the part moving to the first pierce point and going through until it starts moving:

N0090 G00 Z1.0000
N0100 X1.0376 Y-0.7923
N0110 Z0.1500
N0120 G28.1 Z0.12
N0130 G92 Z0.0
N0140 G00 Z0.1250
N0150 G92 Z0.0
N0160 G00 Z0.1500
N0170 M03
N0180 G04 P0.1
N0190 G01 Z0.0600 F100

[drieslaas]

That looks almost exactly as I thought it should.

I shall metrify it and test.

Thanks a sixteenth,

Dries

[I Lean]

It looks like the only differences are that you are zeroing the Z axis at pierce height, and again after the move to cut height.

You also mention lifting the torch from pierce to cut--that's backward, pierce happens higher than cut.