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  1. #1

    CNC Conversion - which path to take

    Hi All, I would like some help, mainly conceptual regarding CNC conversion of a milling machine. As I understand there a number of options of which I know 2 of, to some extent.

    1) one of my machines have a Mitsubishi PLC - this seems to me a little cumbersome in respect of setup and programming
    2) I have added CNC functionality to an old Berco Surface Grinder using a DSP0501 and couple of Stepper Motors - this seems a simple solution but this is open loop which is a concern on the vertical axis especially
    3) Someone suggested a CNC9640 controller with Servo Motors or Hybrid Stepper motors
    4) Another suggestion I had is using a pic32 controller with Hybrid Stepper motors

    The first one I use on the daily bases and at this stage I am not impressed with the system as it seems like a whole lot of electronics for very little automation: The machine has a control panel that consist of a few dials and buttons and allows to set a depth in mm using 2 dials to nominate the boring depth starting from the current position . My first wish was to have the machine remember its starting position and have a button assigned to reposition the head... well it doesn't appear to be a simple task

    The second is simple and working fine but would be better with a larger interface and be able to set parameters instead of loading a G-Code sequence and running it

    I was told that option 3 or option 4 would do what I need:

    I would like to add CNC control to a New Surface Grinder/ Milling machine.
    Optimally the machine would have a screen where the user can:

    1) confirm the the head is in starting position - Call it "Zero" ( X and Y) which is a position relative to the current work-piece
    2) enter the length of the work - the head should travel from Zero on X
    3) enter the number of passes the machine should make
    4) enter the height adjustment the machine should make after each pass ( Y- axis - lower the head before the next pass)

    What are my real options to achieve the above?
    Should I look at something else?



  2. #2
    Community Moderator Jim Dawson's Avatar
    Join Date
    Dec 2013

    Re: CNC Conversion - which path to take

    I'm a little confused here, are you wanting to retrofit a milling machine or a surface grinder? Or both? The two machines are really controlled differently from a functional standpoint. Same control hardware, but the G code would be different. A surface grinder could be set up with some simple step & direction controllers and some movable limit switch cams for the table travel, and a little relay logic to move the head down for the next pass. But this would be more complex than simply using some off-the-shelf CNC software, and standard G code.

    There are a number of inexpensive CNC software/hardware options; Dynomotion, Centroid Acorn, or Mach3/4. Any of these would be compatible with closed loop steppers or step & direction input AC servos.

    From here, the options are endless and are increasingly expensive up to crazy expensive. It is possible to use battery backup absolute encoders to always know where the position is, even after power down. But this gets into the crazy expensive area.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3

    Re: CNC Conversion - which path to take

    Hi Jim
    Thanks for your reply.
    It is a automotive surface grinder and milling machine (segmented stone grinder and fly cutter)
    The requirements in respect of motion control complexity are much the same as an engraving machine would have.
    There is one spindle and 2 axis.

    1) The spindle speed just need to be variable/adjustable and that is easily done by a VFD

    2) The X axis is also relatively simple, an electric motor with a gearbox driving it and the only thing we must know is a rough position of the carriage, 1-2mm +/- is not an issue so I think a linear scale would be great as long as its data can be utilised by the system

    3) The Y axis is the one where it needs the accuracy. We need to be able to have the ability to accurately position the head, and make small adjustments to the vertical position during a job

    I understand there are controllers that use G-Code and I have done one system already with the DSP and stepper motors but here I like to be a bit more sophisticated

    We need to have loop-back as if the head positioning is not correct, we have to abort the job. Not sure what is better to use, would a Hybrid Stepper motor or a linear scale or perhaps the 2 together provide a solution?

    I also would like to have a simple interface that doesn't require someone to read and write G-Code

    Ideally the user would be able to define say max 10 passes
    For each pass would be able to nominate a head position decline value (like 0.02mm, or 0.1mm)
    and a speed for x axis and run the machine
    On a windows machine it would be no problem, I have done many years of programming, but no idea what hardware would get me close to this solution?
    If this can be done by a Mach3, Mach4, pic32 or whatever controller, than that would be an option.
    Can this be done using a PC?
    How would the PC interact with the controller?
    Any help would be greatly appreciated,

  4. #4
    Community Moderator Jim Dawson's Avatar
    Join Date
    Dec 2013

    Re: CNC Conversion - which path to take

    OK, now I understand what you are doing. In another life I was an automotive machinist (about 50 years ago), so am familiar with the process.

    This Van Norman is like the machine that we had in our shop.

    I would look at the Dynomotion motion controller, it is field programmable, and has a Windows API. Another option would be Galil motion control products, also field programmable and has a Window API. I use Galil products in my machines. You would need to write your own custom UI. I use Microsoft Visual Studio (free version) as my programming platform. Using this, you can write code in the language of your choice.

    Given the requirements of the application, it might be better to close the loop at the controller using a linear scale as you suggest. Optical, magnetic, and capacitive linear scales are available. My personal favorite is 1 micron magnetic scales, I use these on all of my scale equipped machines.

    You can use stepper, hybrid steppers, or AC servo motors. All of those can be closed loop at the controller level.
    Jim Dawson
    Sandy, Oregon, USA

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