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  • CNC Mechanical issues...

    While debugging my electrical issues elsewhere I thought some advice would be good re mechanical table issues I have.
    These Pics are of some 20mm holes I was popping this afternoon while the electrical gods were on my side
    Material is 1.5mm zintec steel @30A 3800mm/min although I think sheetcam cut that to 3610mm/min due to radius etc.

    Front


    Back


    Cut height was 1.5mm which is the minimum recommended by the mfg.

    While there is very little dross, there is considerable uneven bevelling and a very odd flat spot on one edge which is repeatable.

    Cuts were made anticlockwise, expecting the 'good' part to be the plate not the punchings.

    There is a 6mm lead-in and out but this is not coincident with the flat spot.
    If it does'nt fit, hit it.
    https://ddmetalproducts.co.uk
    http://www.davekearley.co.uk

  • #2
    The first thing to do is to replace the torch with a marker or scribe and run the part. That will tell if this is a tool path or cutting problem.

    Comment


    • #3
      Appears to me you may have some backlash issues?
      Max.

      Comment


      • #4
        Originally posted by jlevie View Post
        The first thing to do is to replace the torch with a marker or scribe and run the part. That will tell if this is a tool path or cutting problem.
        When I was waiting for the plasma torch to arrive a while back, I had a biro in the holder and it ran very intricate tests all day, and worked very well.

        The only difference here was that I underestimated the speed needed and the tests were run at a leisurely 2000-2500mm/min and these cuts were faster at 3600.
        If it does'nt fit, hit it.
        https://ddmetalproducts.co.uk
        http://www.davekearley.co.uk

        Comment


        • #5
          Originally posted by MaxHeadRoom View Post
          Appears to me you may have some backlash issues?
          Max.
          That's the odd thing, apart from a slight wobble in the floating z axis/torch mount, it's pretty firm all round, not perfect but pretty good, certainly no loose areas of movement. I found it odd that it only showed up at that point on a circular cut.
          If it does'nt fit, hit it.
          https://ddmetalproducts.co.uk
          http://www.davekearley.co.uk

          Comment


          • #6
            Which way are the X and Y coordinates on that part?
            Amount of experience is in direct proportion to the value of broken equipment.

            Comment


            • #7
              The top picture is as it was - up/down is Y and left/right is X.
              If it does'nt fit, hit it.
              https://ddmetalproducts.co.uk
              http://www.davekearley.co.uk

              Comment


              • #8
                Originally posted by Davek0974 View Post
                When I was waiting for the plasma torch to arrive a while back, I had a biro in the holder and it ran very intricate tests all day, and worked very well.

                The only difference here was that I underestimated the speed needed and the tests were run at a leisurely 2000-2500mm/min and these cuts were faster at 3600.
                I'd suggest repeating the test, at about the same point on the table as when the cuts were made, over the entire speed range. You may find that path following suffers as the speed increases.

                Comment


                • #9
                  Will try that, thanks
                  If it does'nt fit, hit it.
                  https://ddmetalproducts.co.uk
                  http://www.davekearley.co.uk

                  Comment


                  • #10
                    Increase the look ahead if you are travelling that fast.
                    .

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



                    Comment


                    • #11
                      Knowing squat at the moment!, your torch leads not dragging is it?
                      Mark

                      Comment


                      • #12
                        Look ahead is definitely something you need to look at. I assume you are using Mach. I have had issues like this when Mach runs fast. It starts to cut corners. Also try selecting exact positioning.

                        Comment


                        • #13
                          Great stuff, I have not touched the look-ahead setting yet, will head that way Thursday when I get a chance to do some more tests.

                          The torch lead is suspended from above with a little slack so that should not be causing drag.

                          Thanks
                          If it does'nt fit, hit it.
                          https://ddmetalproducts.co.uk
                          http://www.davekearley.co.uk

                          Comment


                          • #14
                            Originally posted by jlevie View Post
                            I'd suggest repeating the test, at about the same point on the table as when the cuts were made, over the entire speed range. You may find that path following suffers as the speed increases.
                            Having finally beaten the electrical gremlins today I ran this test and the results were still good all the way up to 5000mm/min so it appears the transport is reasonable with a pen fitted.

                            The torch cut still seems poor, these were the results after some fooling around (rear views)...





                            The dross does knock off easy as can be seen in the first part of this one...



                            There are lots of issues here that even my minimal knowledge can see.

                            A fair amount of dross,
                            Wobbly cuts that do not appear to mechanical,
                            Severe edge bevel that varies as the cut goes round,
                            When stacked up, the parts are different sizes, slightly distorted in places,
                            The poor cut seems unaffected by cut speed from 3300 to 4000mm/min,
                            The cut was worse at 2mm cut height,
                            The best cut seems to be at 1.5mm height, 1mm gave no improvement at all.

                            So, I need the voice of CNC plasma experience here to guide me in a direction for tests/checks etc.

                            Can anyone offer advice?

                            Thanks
                            Last edited by Davek0974; 03-21-2014, 04:13 PM.
                            If it does'nt fit, hit it.
                            https://ddmetalproducts.co.uk
                            http://www.davekearley.co.uk

                            Comment


                            • #15
                              I DONT KNOW ANYTHING ABOUT PLASMA CUTTING.
                              Here is what I would try ,pick your longest axis and make a long STRAIT cut then cut over about an inch and return on the long strait axis .Keep repeating and adjusting your variables until you get a good cut. If you cant get a good cut on a simple thing like this ,it would seem that the trouble is in your plasma torch..I hope this makes sence ,good luck, Edwin

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