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  1. #1
    Join Date
    Sep 2016
    Posts
    4

    Z axis, floating head limit switch

    Hello all

    5x10 build almost complete, except for z axis. now here is where the newbie kicks in......

    with a floating head, i understand torch lowers till touches the plate, head raises till limit switch trips. and with the known distance to the switch, this sets zero......

    now the newbie question, is their still a upper and lower limit switch to stop the z axis?
    1.) from raising too high, and running out of threads, and
    2.) if for whatever reason misses plate, and the float limit doesn't activate, so that it doesn't bottom out the threads.



    or is overall upper and lower a setting in mach3/sheetcam?

    and bonus question, if it is 3 seperate limit switches used, does someone have a basic wiring digram for

    thanks in advance

  2. #2
    Join Date
    Apr 2003
    Posts
    540

    Re: Z axis, floating head limit switch

    You really don't need a limit or home switch on your Z for plasma. Doesn't hurt if you do in case of bad code or other error I suppose. Your Z will lower until the torch touches the metal and the floating head rises and triggers the switch and then raises back up and sets your z to zero. Your floating head switch will be a separate switch from any homing or limit. For the homing and limit the same switch can be used. Another productive safety addition would be to fabricate or buy a magnetic break away torch mount and have a switch mounted there to sense the breakaway should it occur and signal a stop wired to your emergency stop circuit. Breaking a torch can get expensive. Specific wiring diagrams are pretty easy to find on the forum for any of the circuits mentioned.

  3. #3
    Join Date
    Sep 2016
    Posts
    4

    Re: Z axis, floating head limit switch

    Thank you

    yes, a breakaway is going to be put on the z, still have to workout the kill option, for when it breaks away... but not to that point yet, so haven't really researched it yet

    that helps some but opens more questions.
    I have been running a plasma table for years, a early 90's model with very limited, and very basic functions. has its own propitiatory software with hardly any editing allowed.

    when the table is shutoff the "parked" position is X-axis to the west, Y-axis to the south, and z axis in the down position. when the software is started, it seeks the opposite limit switches z to up, x to the east, y to the north, then to the "home" position, which is approx 4 back from the limit switches.... before a sheet can be loaded you have to send it back to the park position, due to the design of the gantry.

    so that is where the next question comes in.... with mach3/ sheet cam.... after the computer is turned on and the software started, does it try to seek the upper/lower limit switches for the z axis?, or another way to ask.. upon startup how does the system know where upon the axis it is in the z axis?

    and for those that don't run the upper and lower limit switches on the Z-axis. what would happen worst case scenario if the torch head misses the sheet, or a code malfunction and the lead screw bottoms out? would the stepper run out of power before something breaks? or would parts and pieces start flying. lol

  4. #4
    Join Date
    Apr 2003
    Posts
    540

    Re: Z axis, floating head limit switch

    You can put your home x y and z position switches at either end you want. It won't do anything until you tell it to reference (go) home. You can set each axis up to home in any direction you want. You can then set offsets or "tool change" positions anywhere you want. Home the machine and then go to any offset or your tool change position to load material. Having the ability to have multiple offsets can be handy if you have fixtures for specific jobs or sheet sizes that you use regularly. Mach3 (and UCCNC) are both pretty flexible as far as offsets. You will also be able to swap X & Y to whatever axis you wish and plus/minus whichever direction you want. Don't know what type of table/software you have, but it sounds pretty basic and Mach is pretty option filled and offers the ability to configure everything to fit your needs.
    I would use only a upper Z limit/home switch and then set your soft limit in Mach3 (in this case for your neg Z) for just below the top of you water table or slat height. Then when the torch missed the metal and continued it would reach your soft limit and stop the machine and await you to reset Mach 3 so you can jog to a safe location or home it. There wouldn't ever be any continued Z dive/movement. If it caught in a opening during a cut for some reason, your breakaway would also provide protection and stop Mach and await reset. Just wiring the breakaway in with your watchdog or stop switch circuit will work.
    Good luck!

  5. #5
    Join Date
    Sep 2016
    Posts
    4

    Re: Z axis, floating head limit switch

    sorry, missed your reply..... thank you so much!!! it all makes sense now

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