plasma cutting thc, arc good signal

New features
1

Hi Les,

I’m currently implementing my own torch height controller. It will be
integrated into the main CNC and uses the analogue output normally used for
spindle speed to set the nominal tip voltage. This way it will be possible
to save the cut height (voltage) together with the tool parameters instead
of having to adjust a trimpot manually.

What do I have to do to tell the postprocessor to output something like
this:

G0 Z[pierce height]
M3 P[pierce delay] S[voltage]
G1 X…Y…
…
M5 P[end delay]

where […] is replaced by the corresponding variable. Currently, SheetCam
has no parameter for “voltage”, so I could use the cut height multiplied
with an arbitrary factor, for example 10.0 means 100V. My problem is that
the postprocessor normally outputs a G1 F[plunge rate] to the cut height or
a ramp lead in after the M3. I would like to control this with the THC and
set up the parameters in the M3 macro. So I have to know the cut height
before M3 is called.

Another question: How is a flameout condition usually handled. The
controller can stop the machine when the “arc good” signal goes inactive.
But starting a new pierce at the current position is probably no good idea
as it leaves a burn mark on the workpiece. Starting all over again is also
not good because there’s no matierial below the initial pierce point so the
arc might not transfer or go out again. Should I go back just to the end of
the kerf and try to restart the torch without pierce delay? Or is it common
practice to simply throw away the whole workpiece in this case?

Regards

Bene

–
Benezan Electronics, Stauffenbergstr. 26, D-72108 Rottenburg Baisingen
CNC- und Steuerungstechnik, Elektronikentwicklung

2

Hi Bene,

This is all done in the post processor. I have attached a post that should hopefully do what you want. Note that I have made the S word modal so it only appears when the height changes.

Another question: How is a flameout condition usually handled

It depends on the controller. With some you have to restart from where you stopped. Others, such as Mach3 can back up along the cut path. You manually back up to the start of the cut and restart from there.

Les

3

This is all done in the post processor. I have attached a post that
should hopefully do what you want. Note that I have made the S
word modal so it only appears when the height changes.

Hi Les,

thanks a lot for the quick response. I didn’t know that’s so easy. Is there
a list of available postprocessor features and variable names? If so, I
could find out the solution on my own, next time.

BTW, sheet cam is great! I haven’t bought a license yet because I don’t have
a plasma cutter of my own. The THC development is for some of my customers.
They will surely buy some as soon as everything is ready. I’ll recommend
your program as often as possible.

Regards

Bene

–
Benezan Electronics, Stauffenbergstr. 26, D-72108 Rottenburg Baisingen
CNC- und Steuerungstechnik, Elektronikentwicklung

4

Posts are written in the Lua macro programming language <www.lua.org>.
They have a manual but it is quite hard work to read. If you look in
c:\program files\sheetcam\posts there is a rtf document that describes
the SheetCam extensions to Lua.

Les