THCAD-10

Dee436 wrote:

Thanks both, I will look at the manual and give it a try tomorrow

So in halmeter or halshow, you should be able to locate the encoder count pin and it should follow the expected frequency eg idle it should bounce around near the 0 volt frequency on the calibration sticker (adjusted per the 1/32 link on the thcad) and with a 9 volt battery it should be close to 90% of the difference between the two calibration readings plus the 0 volt offset.

Ok, here is the current situation.

Using the code uploaded by Islander261 earlier in the thread that uses the scale component. I applied my thcad figures and I my output figures in show hal are within .0006 at 0v input and .04 with the 9v battery on the input.
So the thcad does seem to be converting the volts to a frequency that is being picked up and scaled correctly, which is fantastic.

The question now is, how do I let Linuxcnc know what voltage I require and how do I then get it to drive the z axis in relation to this.

I am assuming I can add a signal and link this to a pyvcp screen where I can input a value, I then somehow get Linuxcnc to check the value of that signal and compare it with the output of the encoder. Based on that comparison the Z axis would be driven to try keep the 2 values equal.
But I would need to make sure the thcad could only control the z height, after any pierce operation has completed and the torch is at its initial cut height with arc ok and moving.
Control of z would need to cease at torch off

Looks like I need to do some more reading

I also noticed the green led that confirms 5v, is orange on my thcad10 but I checked and I have 4.8 v.

Dee436 wrote:

The question now is, how do I let Linuxcnc know what voltage I require and how do I then get it to drive the z axis in relation to this.

Welcome to the confusing world of plasma control with Linuxcnc. There are many ways to skin this cat. There are a few configs that have been around for a while but none of them are in the core code but the components that are used sometimes are.. There has been a lot of work by a few over the last couple of years to step to the next level and use custom written components and PID based torch height control taking the torch voltage as a feedback signal.

Probably the most promising one from a stable config that might make the cut to master branch is the one written by PhillC and currently being tested by Islander261. You will find it under a heading "Another plasma component"

To use this config you will need to learn how to compile LinuxCNC from source. That in itself I think is a very useful skill to have and once you get the dependencies sorted, you can upgrade linuxcnc with just a few command lines

But conceptually, you need to turn your Torch on with motion.spindle.0.on which will turn it on with M3 and off with M5.
IF you get that far, you will be able to cut thicker material without a THC

Move to pierce height, turn torch on, wait for ArcOK, wait for pierce delay, drop to cut height and start cutting
About 1.5 seconds later, sample the torch voltage, waiting until the cut speed is near the commanded velocity.
Then enable a THC that takes that sampled voltage and adjust the cut height to the very accurate linear relationship of arc voltage to cut height. This is generally accepted to be about 10 volts per mm. So then if the velocity falls to say < 90% of the cut speed, disable the THC to stop diving on corners. So to get all of that done, you will end up writing quite a bit of code and a lot of time.

PhillC's branch has done the heavy lifting for you and has rolled up just about every feature we've experimented with over the last couple of years.. I've got every confidence PhillC and Islander261 will nail this in the next week or so and produce a kickass config.

Good luck

Hi Rod

Thanks for the reply.
I do already use M3 and M5 for the torch control, I also have initial height sensing and pierce delay all incorporated. I am regularly cutting parts and now have a job to cut around 300 parts from a number of full 8x4 plates. The plates are 10 mm so highly unlikely they will be straight, hence the reason I was looking for a quick way to incorporate some form of thc.
Until about 5 months ago I used to work in IT, so compiling and writing code are not too difficult for me , I also used to have a cnc mill and am happy hand writing G code. With time I will learn what makes Linuxcnc tick just not quite there yet. For the moment I just need to use the machine so will try to get something working with the example from islander261, or one of the other components out there. I will however keep an eye on the config PhilC is putting together for the future.

Darren

Hi

I have been testing the plasmac branch for the last week. I am using it with Mesa 7i76e and THCad cards on my machine. At this point I am chasing Phill into getting probing on thin sheet working. The THC is quite awesome, easily the best I have seen out of the box. I think it is worth a shot if you are going to be cutting 10mm plate, the floating head should work fine on plate that thick. Yes there is a catch in that like very other plasma application you will need to fix your .hal and .ini files to work with your hardware. If you have a working configuration this is quite easy.

John

Hi John

Thanks for the reply, the thc component your trying sounds like it will definitely be the thing to have and something I will definitely be looking to try. Unfortunately att the moment I have very little spare time to put into learning Linuxcnc, things should hopefully improve somewhat by the end of the month. To be honest the first time I saw Linuxcnc was just over 2 weeks ago and I will admit I am currently quite lost with it. I do have a config that allows me to use the plasma and am wary of messing about too much until I have the knowledge needed, loosing the plasma at this point would put me in a world of pain.
I used the config you uploaded and that shows me that the thcad is correctly wired and my calculations seem to be accurate in terms off having the correct offset etc. I am using pretty much the same setup as you but 5i25 and 7i76 rather than 7i76, so it was easy enough to adapt what you uploaded. Where I am totally lost at the moment is what to put in the hal and Ini to drive the z axis based on the output of the encoder and make the thcad usable. If I could even get some basic height correction for the short term I would be very happy.

Darren

Ok

You will have an easier time using one of the established plasma configurations than "rolling" your own. You already have most of the work done with working machine movement. Again I would use Phill's plasmac, it is very complete all you will need to do is use your mechanics hal file and make a few connections in the plasmac.hal and you are done. The other choice is Tommy's toma configuration, I believe he has one for Mesa hardware now.

John

Ok

Well at least two of you have told me to try the plasmac branch, so I am going to take the advice and give it a try.

Hopefully I can get a couple of hours this weekend to get it set it up and try a few cuts. I appreciate the help and advice and will let you know how I get on.

Darren

Dee, I reckon you should take the time to learn how to checkout LinuxCNC master branch from git and compile from source and run that via run in place . Thats the only way I've ever run Linuxcnc and only after some amazing guys on this forum helped me compile the PREMPT_RT kernel from source! You should end up with the source and the working config in a folder called ~/linxcnc-dev. I'm not 100% sure but from what I understand this will not affect your current working config at all But keep a backup copy of your config folder.

Once you get that far, get your existing config working via run in place (which may need some minor changes if you are using V 2.7.

So from that point, you should connect to Phills git repository and checkout his code into a different folder (~/plasmac comes to mind).
Then from that folder compile his source and the plasmanc config will be contained only in that folder so it will be easy to swap between configs using the correct rip-environment script.

Watching from the sideline for the last couple of weeks, Islander261 and Phil have just about nailed it with plasmac. Tomorrow I am really hoping to get ohmic sensing working on my home made table and then I'll be doing exactly what I'm advising you to do. The reason why I recommend this course is people like Islander and myself and others have done a lot of work on plasma over the last couple of years which Phill has pulled together into a single cohesive config.

This pair make a great combination becasue John the Islander makes a living out of cutting stuff on his plasma and one of the few guys in the open source movement that totally understands plasma so with Phills coding skills building on the assistance I and others have provided John, I reckon this is a real winner to back. For John to praise Phill's THC code the way he has when he is already on record stating that his home grown LinuxCNC is performing way better than other commercial THC's he's used, hacked and studied in extreme detail says to me that this is the way forward, Embedded somewhere in this config is months of work by Dewey Garrett one of the lead LinuxCNC developers trying to guide me on the other side of the world to use the then experimental External Offsets branch to do THC on a crappy Chinese Plasma. Sadly Dewey's hpid component I use did not make the grade outside of my prototyping workshop and is deprecated from the main code but all of the learning are alive in Phills' config. I can't wait to catch up with it but like you my time is also really limited right now.

Finally, let me say that you should have no problem cutting 10mm material. I've cut heaps of 8mm and dialed my 120 amp machine in on it. and I've also cut 16mm without problems. The real Issue I have had is touching off on 2mm steel in the absence of an ohmic sensor. Now I have a machine that can do Ohmic, I reckon I will solve that problem with some rework on my my macine just in time to cut a few hundred parts out of 2mm that I used to outsource to a laser cutter.