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basic CNC questions

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  • basic CNC questions

    i'd like to try to build a CNC plasma cutter and would like to know what i'm getting into. i imagine it is very similar to alot of the CNC milling discussions, and i hope to find some experience here.

    3'x3' CNC cutting tables cost about $10,000 -- without the plasma source or computer.

    given the following, how much might a guy spend?

    first .. i'd be pretty darn happy with a 1/16" accuracy. how sloppy would acme thread be? do i really need ballscrews?

    i dont think i need alot of power. the torch is pretty light. i need everything to move quick (~40 to 100"/min).. and have very little inertia. ie the torch/head would have to change directions pretty darned fast. any 'lingering' will burn a hole.

    i'd prefer to 'scrounge' for as much as possible. i have access to alot of old laser printers / copiers / office equipment.. anything in there i could use?

    free software anywhere? recommendations?


  • #2
    I have been building one now for about three years. Got all the parts laying about here and there.

    Friction reduction is the one cool thing about ball screws. UHMW sliders like the one I built for less than $100 will work.

    I have built two more sliders like the old style, out of 2x2 square tubing. Rollers (inline skate wheels) carry the load. It does not take much of a motor to move a plasma cutter, about 250oz motors will do fine. Gecko 201's are as good as anything on small motors. On the larger ones I still think not. The cheap drive I bought off ebay didn't have the speed of a gecko.

    I did post pictures? I don't remember. I got a lot on my plate right now. (just brought in another 24 sheets sheetrock) the bedroom, bathroom, and the basement. I think the basement will wait till after I do a few union jobs and get caught up.



    • #3
      There are loads of plans out there on CNC routers.
      Some are free and some are paid for. You can always crib ideas from looking at machines on the web.
      Ballscrews are a must as you need speed and throwing an acme screw at speed reduces the effiency.
      This is if you use screws, some designs use timing belts with the carriage fastened to the belt.
      Others use rack and pinions or even lengths of timing belt as a rack.
      Many, many choices.

      Rails can be proper linear rails, tubes with nylon rollers or even square box mounted corner up and two ball races running on two adjacent faces.
      Many, many choices.

      My personal choice would be the box section rails, off the shelf bearings, timing belt drive on both sides of the main axis powered by a stepper motor with geared jackshaft to stop it crabbing.
      Other axis similar but only powered one side as it's narrower.

      All the rails mounted well above the table with the head hanging, this way the rails are clear of the crap and crud.
      Also gives you table clearance to slide a sheet in under the rails.

      Software has got to be Mach3.
      This is the only affordable program geared to plasma.
      It has reverse if you need to go back and also torch hight control for the sheet.


      John S.

      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


      • #4
        thanks for the input guys.

        can you give me the big picture on information flow? once i draw, say, a bracket in my cad program. where does the drawing go from there?

        poked around for Mach3 with no real luck. do they have a website? am only finding references to the software but no details (price, etc)


        • #5

          Save drawing as DXF file, import into Mach3, convert into cutting strategy, then cut.

          Mach3 is to be found at:-

          There is a brilliant manual available on the download page.
          DXF import is handled in Chaper 8.

          Cost of a licence is $149.00 but the demo is uncrippled except that it's limited to 1,000 lines of code before it stops.

          Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


          • #6
            I'm running Mach3 here on my bridgeport. I like it. I have had a couple of minor problems. Most the problems come from Windows.

            Not tried the "jpg" cut feature or the Plasma cut program in it thou. It does have a converter. The Yahoo group has plenty of information and you get to pick the brain of the code writer Art. he is a nice guy. He has worked out several of my Mach3 and not-Mach3 problems.

            The License if worth it. I went through 3 software changes before I settled on it. I didn't like however going back to Windows. I feel Dos is much more stable. Single tasking and single dedicated. Turbocnc is a simple dos program, the demo runs fine but you are encouraged to register it. It is wrote in borlands turbo Pascal. But as most users never see the working end of that code. It works as is.



            • #7
              oh boy, i've got a funny feeling that money is about to be spent.

              i'd like to go the PC route, not the big black box. i understand that the motors need controller cards, and my PC will use the printer port.. does the printer cable plug right into the controllers? if so, i dont have two printer ports on my computer! what now?

              so 250oz (1.8Nm) motors should do it?

              i'm hoping i wont need a 3rd axis for plasma. i'll be experimenting today. built a 'linear guide' with two heads, one for the plasma and one for the oxytorch.. 3' long, uses an old bosch drill motor and the head from an angle grinder to get me to decent speed/power. the drill trigger can do some speed control.

              going to try straight cuts today and see if it goes well.



              • #8
                john, i've been doing alot of reading and its starting to make sense now.

                any good suppliers in the UK (website, etc) that sell kits?

                took a good look at the MACH2/3 software and i like what i see.