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  1. #1
    Member
    Join Date
    Jan 2021
    Posts
    6

    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
    567

    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
    6

    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
    Registered
    Join Date
    May 2015
    Posts
    567

    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
    Member
    Join Date
    Jan 2021
    Posts
    6

    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

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