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Old 07-20-2017, 09:37 AM   #61
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Well, I had a bit of a rethink about the ohmic sensor on a torch that does not have a shield as its the cutting tip that hits the plate so I moved onto other things. I spent a day and a half last weekend soldering up all of the connectors on the case



And an SMA coax connector for the wireless pendant closer to the top of the enclosure.



I had one stuffup that cost me hours trying to work out why the gantry was not homing correctly. Eventually today I worked out that I had accidently plugged the 5V stepper controller wiring back into the wrong controllers so stepgen 0 n the 7i76e was wired up to joint 1. This was OK except that the home and limit switches were unaffected. so when we homed, the wrong switch was triggered so the wrong motor kept running.

That will be all double dutch to anybody that is not using the new LinuxCNC joint axis homing sequence for gantries. What happens when homing is that the gantry heads towards the homing switches and when the first side hits the homing switch, it waits for the other side to catch up. Once it catches up, each side moves to the specified offset and then home is set.

The good part about this is that you can home the gantry in software by altering the offsets. In my case, the offsets were different by 2mm between sides to square the gantry.

The problem I had was the wrong side was trying to catchup which did not work very well... :cry: I only worked it out after I really slowed down the homing velocities so I could see what was going on.

Anyway, If I can massage a Sheetcam post processor, I might even be able to cut something this weekend! But don't hold your breath as I've got a busy few days coming up!

I also have a couple more wires to add to the cabinet for the 5th axis and a couple more things so I can seal the cabinet up once and for all. None of these are critical for the present config though.


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Old 07-22-2017, 07:25 AM   #62
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Its Alive!

https://youtu.be/zVM5Tz4Tzm4

We had a lot of trouble this morning. I've had the machine torch for 12 months but this was the first time I had plugged it into the machine. The torch came on with the machine and would not go out. Then we tested the hand torch and we could control it from LinuxCNC without having the trigger pressed. So after comparing wiring between the two torches, I cut one wire inside the machine torch so it looked like there was a switch turned off and everything worked perfectly.Well it sounds simple but the process took several hours of troubleshooting!

I've still got some things to sort out. I'm not sure why the flame goes out on startup. We did edit the gcode a bit and got the outer circle to cut perfectly.

I was not seeing an ArcOK signal or a torch voltage. I hope it is just a wiring fault in the cable I made up.

I spent about $300 on air fittings in preparation for setting up an engraver but that can wait for a while...

I have so much work to do to set up Sheetcam and work out the right cutting speeds.


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Old 07-22-2017, 01:00 PM   #63
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That's great to see running. I believe you will get the rest of things sorted.

Thanks again for posting this thread and all the details.

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Old 07-22-2017, 11:59 PM   #64
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Good to see it up and running Rod. I'm sure you'll get on top of those teething problems .
Cheers
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Old 07-23-2017, 06:06 AM   #65
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Impressive to see it moving and cutting! Awesome work. Teething problems ... pah! After what you have achieved to date I can't seem them evading you for long.

Cheers,
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Old 07-23-2017, 08:49 AM   #66
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Thanks guys, James, you are right!

I knew nothing about Linux CNC
I knew nothing about CNC in general
I knew nothing about Gcode
I knew nothing about Plasma cutters

But today I managed to cut a donut!



I solved the torch voltage issue by plugging in the connector. What a dope!

Then I found one of the Arc OK signals had been soldered to a pin in the interconnect cable that was not connected inside the plasma cutter! I wonder who did that?

Because I knew nothing about my plasma cutter, I did not know that it tries multiple times to establish an arc with a pause in between. So the reason why part of the cut was skipped at the beginning was that I was attempting to pierce too high and the plasma cutter did not get a good arc and turned off and retried just as we were started moving. Lowering the pierce height to 3mm fixed the issue.

I'm still not convinced I've got the ArcOK signal working properly, but that won't take much to sort out and then hopefully, I can say the wiring is finished. Here's just a small part of it.

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Old 07-31-2017, 06:53 PM   #67
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I did not get much done over the weekend or so it seems

I wrote a small program to make a series of cuts at different speeds


I started with cuts at 100 mm/min apart, zeroed in on the best looking one and then repeated (several times) at 10 mm/min apart.

So now I have the machine dialed in for 2mm mild steel. As part of this, I told LCNC to log the torch voltage (at 1000 times a second) I kinda forgot about this for a while and the next thing I knew was I had an 8 gb text file!

I also was able to do a bit of debugging of some signals and checked the code for one component I'd written becasue I was only showing a voltage of about 20 volts. This was due to a software error in my C code. I was only out by a factor of 20.

I think I need to revisit the calibration resistor in the torch voltage circuit becasue I think the THCAD board is receiving a voltage above its full scale range. After fixing my error, the THCAD should have a full scale reading of 320 volts but I think it is getting up around 400-500 volts on startup.

I need to spend some more time cutting while checking some internal signals in LinuxCNC and also with a volt meter. I did debug a bit more of my config. Some of it I did so long ago, I had forgotten how it worked. I'd added a delay on the THC enable signal and I was able to confirm that all of my THC enabling logic (3-4 things must be true before the THC is engaged).

So once I know I've got the torch voltage nailed, I will be able to look at the Torch height control. Once I get this far, I'll be on my own as I have not seen anybody else using the new experimental LinuxCNC branch on a live machine. I really hope it works!
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Old 08-07-2017, 09:46 AM   #68
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I'm afraid nothing much has happened the last couple of weekends Because I did not have the confidence the torch voltage and dividers were correct. So I decided to hack the probes off a cheap set of multi meter cutters and solder them onto the raw voltage output on the CNC port



This let me plug a multimeter in to read the raw arc voltage while cutting



While I was doing this, I fired up halsampler in a new terminal window and it logged the voltage and a few other things 1000 times a second



And something clearly was not right with the voltage divider. So I pulled the plasma cutter apart to access the CNC board so I could change the divider ratio by changing a link on the board which the manual said selected between 16:1 and 50:1.



And nothing changed! Grrr

So I pulled the board out of the machine and inspected it in the sun to find that the manual was wrong! So a few more testcuts later, neither divider was showing correct results.

So I stopped and phoned a friend and I walked down the road to his place and he traced out the circuit for me. Still with nothing definitive I wandered home quite despondent. The next morning, I spent hours analysing the board and drawing out the circuit. Still with no further progress and after thinking about a few things and a bit of research, I decided That the best way to do this was to connect a known voltage somewhere in the cutting volts range to the board and make some accurate voltage readings.

I had a couple of 48 volt power supplies so I decided to join them in series to get 96 volts.



Pretty close, all 17 amps of it!



So I took a deep breath and plugged it in.



And put a high quality multimeter on the raw outputs.



You can see the voltage dropped a couple of volts because of the 100k resistors on the raw voltage outputs to prevent arcing.

So now I could measure the divided voltage



and I could also read the data back in LinuxCNC. I had a discrepancy for a while until I remembered I had a scaling resistor in the cable and I was reading the voltage after it. Sure enough, when I read the voltage before the resistor it was perfect.

Time to do the maths! No wonder I was in trouble. The dividers were out by a factor of 1.5. The 50:1 divider was actually reading 75:1 and the 16:1 one was showing 24:1.

So A quick tweak of the calibration settings in LinuxCNC and I was getting a perfect result within +- 0.7% on the voltage sensing circuit! Finally! So now I can actually get on with setting this puppy up!


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