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Don't know about the signal issues (probably need JT to help with that), but the negative scale issue is because the THC uses an encoder counter velocity signal to read frequency. The encoder counter is set in up/down mode (A input = count, B input = up/down) the default high state on the unconnected B input makes the counter count down rather than up, causing the velocity to be negative, You can fix this as you did, or by setting the encoder scale to a negative number (or setting the encoder 'B' pin to TTL mode and grounding the B pin)

OK. That makes perfect sense. I didn't think about B being the signal for up/down. So in differential mode would you need to make B+ low(ground) and B- high(+5v)? Or is differential mode even necessary? It's supposed to have more noise immunity.

Thanks,

Tim

I would jumper the B pin as single ended and then ground it,
I would use differential on the 'A' pin (for noise immunity)

Ok. Didn't know you could do that. Guess that's why there are 3 jumpers.

Got it working and it's working good. THC is almost a must have for long cuts. Made a small classic ladder program for the under, ok, over indicators.

link to vid.
www.dropbox.com/s/tgl8bx1dc1qu4vm/VIDEO0054.mp4

nozzle is old but still cutting ok with the thc.

Looking good! I like the scenery outside your door... The THC panel looks familiar...

John

BigJohnT wrote:

Looking good! I like the scenery outside your door... The THC panel looks familiar...

John

Yeah, I like your panel layout. Thanks for all your help.

One thing I may need to do is turn off the THC during the pierce movement. I was cutting some 1/2" steel and the thc would cause the nozzle to dive and touch material until the torch stared moving horizontally. I think I could do it in classic ladder and have the THC turn on when Z axis is below a set point like 0.065". Do you know of a better way?

Tim

If your arc voltage is ok while piercing it should not dive. I guess you could "and" something to block the enable while piercing.

John

I may not be doing things right. I was doing edge starts with a pierce movement and a slight delay. Maybe I shouldn't do that.

You only need a pierce delay for piercing not for edge starts.

John

I started to test my machine. Not the plasma side just yet. I made some changes to your code to work with my own setup but the bulk is still the same.
I found that the Z axis is very sluggish under manual control or jogging. Do you find the same?
What is your server thread time period set to? I think this might have an influence here.

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.

Paul

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.

John

Hi all,
I am using the THC300 config provided in the examples. I use a component in place of the hardware. The component provides the up/down signals as well as the arc_ok signal.

I have a problem that the torch fires while the tip is still on the plate and in the process of pulling up to the cut height. At this time the float switch is still closed as well.
Any suggestions please?