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Plasma Cutter on an ACRO & Blackboard - THC & other issues.

Discussion in 'Laser Cutters' started by Jay Riffs, May 27, 2019.

  1. Jay Riffs

    Jay Riffs New
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    I want to build a CNC plasma table based on the Acro + Blackbox + NEMA 17 motors. Size should be 750x1000 or 1000x1000, didn´t decide yet.

    Could you please take a few minutes of your valuable time and advise me on whether or not it is a good idea, and also answer some general questions? Even if you answer just one of them, already helps me a ton. I did a lot of research (days and weeks on end), but it is still my first CNC project and there are a few probably dumb and obvious points I don´t quite get yet, possibly due to my tendency for massive overthinking. Basically I´ve hit a research wall by now and need some help.

    Gear-specific querstions:

    1. I plan on cutting mostly really thin materials, 1.0 - 3.0 mm aluminium and various steels. To not "overcook" my sheets, I want to be able to cut at up to 7m/min (thats around 275 in/min) and up, which according to my research is a good approach for thin materials. Will the NEMA-17s provide enough useable speed and acceleration to move the gantry & the plasma torch fast enough? I know they do fine even for light milling regarding TORQUE, which is however not per-se interesting for plasma...Could not find any reliable info on the net about SPEED thou. Basically should I even concern myself with NEMA-23s at all for this type of build, or just roll with NEMA-17s and be happy forever after?

    2. With a 750x1000 Acro, what is the effective work area? ???mm x 800mm?

    3. Assuming I get the cutting speed right, will there be a lot of sheet bending at the specified sheet thickness & sizes, leading to a necessity of a THC system of some sort? Does aluminium bend more/less than steel? Some people say you can´t go without THC at all unless you wanna be holding your work down with a wooden stick at all times, others say it´s fine, and some even offer commercially available products (Crossfire) that have no automated THC whatsoever. Bit confusing.

    4. I know torch on/off can be connected easily to the Blackbox. But what about a torch height control module - be it touch before every pierce and then lift, or a fancy THC that controls the height by overtaking your Z-axis entirely and measuring arc current, then moving Z accordingly at all times? If you know some THC modules that fit, which one(s) would you recommend?

    5. Does the Blackbox eat gCode exclusively from it´s dedicated program "OpenBuilds CONTROL" on the computer, or can one also run it with Mach3 or universal Gcode Sender etc. etc.? Not that I must, just asking. Also unlike Openbuilds CAM software, which needs internet, the CONTROL can work perfectly without, right? Just making sure, this is very important.

    6. Is the Acro the best suited (ready) Openbuilds kit for this, or would the Ox be better? Intuitively I say Acro, but who knows..


    Generic questions:

    7. When running a water table under the machine, should one not take great caution for the water not to splash on the drive belts (or screws, or rack) and especially on the motors? It always looks so messy and splashy but I don´t see waterproof..welll..anything around the motors on a lot of machines out there, especially DIY ones.

    8. Are there certain types of torches that provide a better edge finish? I know to buy brand names and not china crap, but beyond that? Some things like specific sub-type of cutters (or cutter heads etc.?) that are maybe less suited for thick materials, but leave a better finish in 1-3mm sheets? Also should I generally opt for a lower-powered cutter, as it is "gentler", such as 35A or 40A instead of 60A? Or is it the other way around, that ESPECIALLY thin materials need lots of power so it gets through fast and can move on and doesn´t overcook the sheet? Ranges below and above 1-3mm I can live without entirely - if it gives me better cut quality in the ranges I need.

    9. I know about not using HF cutters to avoid intereference, but using Pilot-Arc ones instead. Any other pointers in terms of not frying your electronics with the cutter itself, for a first-timer. I am talking about things just a tiny bit less stupid than "Don´t clamp the ground clamp to one of your motors or the Blackbox". Anything below that level of dumb might not be obvious to me yet :)


    Cheers, and huge thanks if you took your time for answering me, saves me a lot of trouble and money!
    Jay from Germany
     
    #1 Jay Riffs, May 27, 2019
    Last edited: May 27, 2019
  2. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
    Staff Member Moderator Resident Builder Project Maker Builder

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    Grbl does not support THC. If your application needs torch height, i would advise digging a little deeper into pocket from the getgo for a controller that would.

    That said, checkout Floating Head / Drag head plasma designs. Discuss the options with your plasma vendor. Many modern plasmas have looped current torches that slide along the material, no THC or air gap needed.

    Acceleration: Nema17s are going to suffer. Keep in mind that plasma cable/hose is a heavy beast to sling around over the table even if suspended from the ceiling.

    Blackbox uses standard Grbl, so any Grbl compatible gcode can work (sheetcam, fusion360 etc)


    On the machine designs, and plasma inverter/torch questions i cannot provide too much input. My advice, lots of research. But figure out the main goal first. Jack of all trades, master of none, remember. What works great for thick 80a cuts won't work so good on 10A 0.5mm sheets.
     
  3. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Oh and just another note: Aluminum suffers severe dross issues under plasma. Unavoidable, its like a heatsink. Milling gives clean edges...
     
  4. Giarc

    Giarc Master
    Moderator Builder

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    Another potential issue is heat. The acro plates are made of acrylic and may not fair as well as aluminum gantry plates.
     
    Peter Van Der Walt likes this.

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