Mesa THCAD With Parallel Port Setup
Hello Guys and Gals,
I need help. Again. I have read through posts, Mesa's THCAD manual, the samples included with LinuxCNC and the man pages for THC. For now, I would like to setup a plasma THC using the Mesa THCAD and parallel port setup with a C-10 breakout board. I have latency numbers around 14,000-15,000, but am not sure if these numbers are extremely good enough for a basic THC setup. I'm not expecting to cut corrugated metal (today , but am looking for something to adjust small irregularities in cutting material, thermal movements during cutting, etc. I do have a floating head setup working and use my post processor for Sheetcam setup to touch-off fairly often to help compensate until I can get some type of THC going.
I may be over my head on this, but I am looking at the config files first trying to see where the physical pin assignments are defined. I am also struggling with the THCAD's divided frequency output setting – Not sure what setting to use. I'm not against getting a Mesa FPGA setup someday, but would like to use what I currently have for now.
Are these questions so basic that not knowing the answers puts me on the should-not-be-attempting-this list? Thanks for any information.
If you read through the other THCAD/parallel port thread there's a
little discussion of the limitations of using the parallel port with the THCAD
Basically it may limit how fast your torch height control can follow material
height variations. (This may also be limited by your Z axis performance)
For a parallel port configuration a free input pin is fed to linuxCNCs encoder
component and the encoder components velocity pin is connected to the THC
component (all in the HAL file)
All of the pin connections are in the thc man page and one of the well documented components IMHO.
My plasma configuration files (using a 5i25-7i76) are here . Also note the touchoff.ngc which is what I use with sheetcam to touch off before a cut starts. I even have the sheetcam post file that I use... I think it is the latest.
OK - Thanks for the replies. I did read a post about the performance of the THCAD using a parallel port, but am thinking that it's better to have a slow thc compaired to no thc. Maybe it just won't work, but right now the changes I need are not much and want to be hopeful that this can work out. Even temporarily until I decide how all this is going to play out for me.
John - Thanks for the files. I have been going through them, but didn't know how much of the 5i25 config files I can learn from to implement into my parallel hal file. I did see your Sheetcam post file, but didn't think it included torch touch-off reference so a touch-off didn't have to happen every pierce. Also, I plan on using a scribe someday which this post incorporates along with some thc control, but I have that part turned off for now.
I will plug away and see how far I can go. Thanks for all of the information all of you have provided. I wouldn't be this far without it.
One important thing is the plasma cutter itself. If it does not provide a pre build reference voltage it could be dangerous to open the plasma cutter and create yourself the reference voltage as the voltage / amperage combination are dangerous.
I am currently waiting to my plasma cutter ends warranty to make this myself!
The biggest changes will be the pin names and you only need the section that connects the output from the THCAD card to the computer. Just change the pin name to match the parallel port pin your using.
Thanks emcPT. Fortunately, my plasma cutter has a CNC port for 1/50 voltage reference, torch activation and ARC-OK. I think the Proma THC unit is designed to be mounted in the plasma cutter if a reference voltage is not available, but like you said - that would be a wait for the warranty to expire.
Maybe you already knew this but if you load the 'Plasma-5i20' sample configuration in Linuxcnc. The 'Plasma-demo.hal' and 'Plasma-demo.ini' files are set up for parallel port. They should get you very close to what you want.
Thanks Coolmo32. I did save those samples and went through the parallel files. I need to sit down again when I get a chance again and go over the 5i20 files, too. As of last week, I haven't been smart enough to see any pin assignment samples getting the THC info in. I just haven't had the time the past few days to sit down and go over John's files for the 5i20, either. I'm not saying the pin assignment isn't there, but I haven't found it yet. I see the pin assignments for everything else: Touch off, torch on, etc.
I was kind of expecting to find a line, generally, like:
net thc-data-input <= parport.0.pin-10-in-not
...or something like it.
in a terminal window, type:
this is the THC manual and lists the THC components pins
Note that no parallel port pin will connect directly to the THC component except ARC-OK.
The actual voltage reading is done by measuring the frequency that the THCAD generates
This frequency is measured by using the encoder components velocity output pin.
So voltage measuring connections are: THCAD --> Parallel port pin --> encoder component 'A' input --> encoder component velocity out --> THC component