Well its been a while since I updated this thread. Once I upgraded the machine, I needed to do 2 things. Add a larger drag chain for the larger torch cable and also to install ohmic sensing to sense the material height more accurately than my float switch.
The plasma cutter came with a clip to connect a wire to the torch shield. Note this is not the actual electrode tip but a protective shield that is isolated from the arc voltage.
The Ohmic sensing took a lot more work than I expected as it required a seperate isolated power supply and a three optoisolated relays. 2 of these isolate the probe circuit while cutting and the third switches field power to an input n my Mesa 7i76e when the torch touches the material. I also added a small circuit board with some protectivediodes and some LED indicators which are now redundant as the relays have LED on them anyway!
I've spent a fair bit of time with some plasma enthusiasts in the Linuxcnc movement working on a new plasma controller written by Phill, a fellow Aussie. He has been amazing with the features he's added from feedback by people like me and there is now no point buying a commercial controller as this is that good and very easy to install.
Whats so unique about this config called Plasmac is that all control is built into the GUI so the plasma cutter just receives a M3 command to start and all probing and torch height control just happens. I have not shown it here but on the Plasma Run tab, I have a list of about 50 cut charts that can be selected from G code or by walking up to the machine and choosing your material from a dropdown. It also has a Statistics tab which tracks the number of piercings and distance cut so you can monitor consumable life or gather data for quoting purposes.
Today I wrote a Sheetcam post processor which found a lack of error checking and while I was workin on the Post, Phil added some clever error checking that checks for invalid tool selection in G code before a cut is made. (Which you can see in the screen dump)
But proof is in the pudding. Here is a part I cut yesterday on a steeply angled bit of material and it had no trouble following the material at the 2mm cut height I was working to just be reading the arc voltage and using a PID loop to control height.
In the next post I'll add a couple of videos but it looks like its about time plasmac did the obligatory cutting of a sheet of corrugated iron!