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  1. #1
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    Join Date
    Jan 2021
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    7

    Plasma Controller

    Good day folks
    i am in the process of putting together a plasma table for a friend of mine. i have a few criteria i need to fill.

    -somewhat inexpensive, i am hoping to put the brain together around 500$
    -the desire to have quality torch height control
    -fairly user friendly
    -it's an everlast plasma and has a CNC plug in the back.

    so far, i think the biggest decision i have to make for him is the software.

    i know mach3, i look at mach4 and find it quite straightforward.
    for what i read, LINUXCNC seem to have better options as long as software integrated torch height control functionality.

    what's the best software to have today ?

    as for the brain,
    my mini-mill, has a parallel port stripped and hooked up direct to my 3 G203V.
    it's safe to assume there will be a need for opto-isolation, is there a breakout board out there that would allow me the good old parallel port connection while offering adequate protection ?
    would it be possible to have signal input for software controlled torch height control ? how is that done ?

    are the standalone torch height controller worth it ?
    i did some research on few of those and found one that some have a quite slow response, and might not have adequate anti-dive capabilities. was i reading lies ?



    thanks for your time

  2. #2
    Registered
    Join Date
    May 2015
    Posts
    601

    Re: Plasma Controller

    I might be a bit biased becasue I have had a lot of input into Linuxcnc's Plasmac configuration becasue I tackled the plasma puzzle before it was conceived.
    There are too many people migrating from Mach and UCCNC to ignore it. Whilst you can run it via a parallel port BOB, you will get much better results if you grab a $119 Mesa 7i96 ethernet board and a $69 Mesa THCAD-10.

    To adopt a Windows solution today is much like buying a VHS video camera instead of one that records to SD cards.

    With Linuxcnc, you don't actually need a THC, all you need is a way to read the torch voltage (via a THCAD-10) and then Linuxcnc's motion controller with sophisticated PID based algorithms can control the torch height. With Plasmac, you get a complete plasma controller, not just a tacked on THC unit. It includes RS485 communications to Hypertherm plasmas, statistics collection and a whole conversational module so you can walk up to the machine and cut simple shapes for flanges and brackets etc.

    I started with an Everlast and if you select the 16:1 divider, then you need to set the THCAD up to read 24:1 (with no scaling resistors) becasue the THCAD sees the Everlast's resistors as being part of its scaling resistance (which is not an issue with hypertherm or thermal dynamics).

    The other thing is that he ArcOK relay inside the everlast has a minimum current requirement of 100 mA. The Mesa card has a high impedance to ground so my recommendation is to add a 90 Ohm, 10 watt pull down resistor from the Mesa input to 0 volts (assuming 24 volt field power). This will ensure 267 mA passes through the ArcOK relay. A cheap way to do this from off the shelf components is to uses 3 x 270 ohm resistors in parallel to give 15 W of power dissipation (it needs to handle 6-7 Watts).

    Finally, the new evolving QTPlasmac touch screen interface is purpose built for plasma control and is very exciting and easy to use.

    Good luck!
    Rod Webster
    www.vehiclemods.net.au

  3. #3
    Member
    Join Date
    Jan 2021
    Posts
    7

    Re: Plasma Controller

    i looked into Linux CNC and Plasmac, it all make sense.

    looks like i could simply do:
    -Mesa 7196 Ethernet
    -Thcad
    -standard Desktop.
    -sheetcam
    in the end, its fairly cheap.

    this definitly fits every requirements, except for the anti-dive.

    what are the workaround for this ?

  4. #4
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    May 2015
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    601

    Re: Plasma Controller

    Anti dive is included.
    Corner lock or velocity anti dive is such a trivial feature to implement in linuxcnc. You monitor the current velocity against the feed rate and disable the THC when velocity falls to sa < 90% of the desired cut velocity

    Void crossing or kerf crossing is also included. I'm not sure how effective it is. I have a different algorithm but its a hard one to test. Lots of cutting required!
    Rod Webster
    www.vehiclemods.net.au

  5. #5
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    Join Date
    Jan 2021
    Posts
    7

    Re: Plasma Controller

    Quote Originally Posted by rodw View Post
    I might be a bit biased becasue I have had a lot of input into Linuxcnc's Plasmac configuration becasue I tackled the plasma puzzle before it was conceived.
    There are too many people migrating from Mach and UCCNC to ignore it. Whilst you can run it via a parallel port BOB, you will get much better results if you grab a $119 Mesa 7i96 ethernet board and a $69 Mesa THCAD-10.

    To adopt a Windows solution today is much like buying a VHS video camera instead of one that records to SD cards.

    With Linuxcnc, you don't actually need a THC, all you need is a way to read the torch voltage (via a THCAD-10) and then Linuxcnc's motion controller with sophisticated PID based algorithms can control the torch height. With Plasmac, you get a complete plasma controller, not just a tacked on THC unit. It includes RS485 communications to Hypertherm plasmas, statistics collection and a whole conversational module so you can walk up to the machine and cut simple shapes for flanges and brackets etc.

    I started with an Everlast and if you select the 16:1 divider, then you need to set the THCAD up to read 24:1 (with no scaling resistors) becasue the THCAD sees the Everlast's resistors as being part of its scaling resistance (which is not an issue with hypertherm or thermal dynamics).

    The other thing is that he ArcOK relay inside the everlast has a minimum current requirement of 100 mA. The Mesa card has a high impedance to ground so my recommendation is to add a 90 Ohm, 10 watt pull down resistor from the Mesa input to 0 volts (assuming 24 volt field power). This will ensure 267 mA passes through the ArcOK relay. A cheap way to do this from off the shelf components is to uses 3 x 270 ohm resistors in parallel to give 15 W of power dissipation (it needs to handle 6-7 Watts).

    Finally, the new evolving QTPlasmac touch screen interface is purpose built for plasma control and is very exciting and easy to use.

    Good luck!

    we did just that, and hopefully i can start putting the "brain" together over the weekend.
    the integrated THC sold it for me.

  6. #6

  7. #7
    Member
    Join Date
    Jan 2021
    Posts
    7

    Re: Plasma Controller

    we're having so much trouble installing everything, Linux CNC is becoming more of a nightmare than anything else.

    can anyone who use this system with a plasma give me a bit of help.
    it looks like i need linux cnc 2.8, which will not work with debian wheezy
    having debian buster(10) seem to create other issues where it won't connect to the mesa without a bunch of work.

    what is the best system to use this on a desktop.
    which OS and version of linux CNC works best with the plasma, and also the mesa ethernet card.

  8. #8
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    May 2015
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    601

    Re: Plasma Controller

    You will get better support if you post on https://forum.linuxcnc.org/

    Here is a video I did on the mesa 7i76e which is similar to the 7i96 which may help..
    https://youtu.be/75tAJ4tdBgs
    Setting up the networking for the mesa card is discussed at about 16:30

    To use the latest version of plasmac (QTplasmac), you need to run master branch (v2.9). Personally, I think Linux Mint is a better platform
    Tommy has a really easy to follow method to install it, patch it with the required PREEMPT_RT kernel and install Linuxcnc master branch here:
    https://forum.linuxcnc.org/9-install...y-installation

    It should only take half an hour or so to get it going and a CNC menu will appear

    Editing the grub menu lets you make the new PREEMPT_RT kernel the default.

    Do the bit about Linuxcnc dev at the end as that will install halcompile which you will probably need. Tommy added that bit yesterday after I had issues...


    So then check your latency to make sure it is say <150000 jitter for a mesa card... Play with BIOS settings to turn off all the power saving and Cstates if it not good enough.

    From there run pncconf to build your configuration. It includes features for plasma configs now. After you get this done, you may need to edit the config files created by hand.
    Rod Webster
    www.vehiclemods.net.au

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