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    Default preserve reference points (home)

    I'm a guy who never shuts down the computers on my mills . What I want to do is break the trigger in pathpilot that requires me to rehome all of the axis upon an estop or a power up on the mill itself .
    I've been digging through the files and I'm sure that I should be able to eliminate this since my lathe which runs on linuxcnc doesn't require me to home on machine start up of the machine .
    I've worked this way for years with mach and I always home the z axis because of drop once the motors power down , otherwise I don't want to rehome all axis unless I've completely shut down the mills and computers .
    If anyone has an idea of what setting controls this then I'd appreciate some enlightenment

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    Member ShortTrack's Avatar
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    Default Re: preserve reference points (home)

    Metalmayhem;

    First of all, I don't know how to do what you are asking.

    Having said that...

    From my seat in the bleachers, I am not sure overriding homing on e-stop or power-up is a good idea. Assuming you have a Tormach Mill, and unless you have added absolute encoders to the mill, the controller has no way of knowing for certain if the mill is where the software thinks it is - if you hit the e-stop or powered up the machine.

    Possibly I misinterpreted why you wish to override rehoming??


    Others??

    -STrack



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    Default Re: preserve reference points (home)

    What I'm looking to do is power off the tormach mills and not the computer , then later fire up the mill and carry on without having to rehome the mill . No position is lost on the control because the control is not shut down .
    I am sure there are arguments against doing what I want to do but this is something that I have been doing on mach run mills for yrs and I can do this daily for months without any lose of position . Except for z which can drop some on shut down , this is the only axis that I want to have to home unless I completely power down the mill and the computer



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    Default Re: preserve reference points (home)

    the point of what I want to do is the fact that I cannot trust the limit switches on these tormachs . I'd be fine with referencing the mill everytime I power it on but I don't care for the necessity of re qualifying parts on 4 machines every single morning . The position isn't lost on the control , nor is position lost on the mill because it is exactly where it had left off . The only difference over the control is the green reference lights go out and I am forced to re-reference . This is exactly what I am looking to eliminate



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    Default Re: preserve reference points (home)

    Changing the mechanical switches to a laser switch would give you more accurate homing. We have a lot of these on the production line but I would have to check if they are repeatable enough for a mill. It would take a knife edge plate to sense. Okomoto and probably others use these for travel trips.
    Unless I have to finish with the same set up I shut mine down, then I just shut off the monitor. It has been really close on rehoming.

    Dave



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    Default Re: preserve reference points (home)

    Quote Originally Posted by metalmayhem View Post
    the position isn't lost on the control , nor is position lost on the mill because it is exactly where it had left off . The only difference over the control is the green reference lights go out and I am forced to re-reference .
    I don't believe that this is entirely correct. The steppers use 10 micro-steps for each of the 200 full steps and powering off the mill will lose track of which micro-step was active at power down. I believe that each microstep is equal to 0.0001 of mill movement so each power cycle could result in loss of position by 0.0009 even if nothing has moved. This loss of position may not be important in a single power cycle but could be very significant over several power cycles.

    You can disable home switches on the Settings tab which I think will achieve what you asked for.

    Another approach might be to attach a dial indicator to each axis, roughly home using the normal home switches and then refine the home position using the indicators.



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    Default Re: preserve reference points (home)

    Quote Originally Posted by kstrauss View Post
    I don't believe that this is entirely correct. each power cycle could result in loss of position by 0.0009 even if nothing has moved. This loss of position may not be important in a single power cycle but could be very significant over several power cycles.

    .
    I've done it daily with my other mills without issue , and it was weeks or months between homing the x and y . I don't mind eventually losing a thou or 2 over time because that is easily corrected . losing .005-.05 on homing is a problem .
    My work around right now is to g53 all axis before shut down the mill , then later on power up I disable the switches and reference the 3 axis , then re-enable the switches .

    There is a no force home in the ini but the pathpilot control seems to be ignoring this . Right now I'm trying to figure out where the command is , IF NO_FORCER_HOME = 1 THEN ................
    I believe the developers have removed the lines that allow mdi and a program to run without it being homed , otherwise in linuxcnc that command allows for jog , mdi and program run if set to 1 . if set to 0 nothing works until the machine is homes . The tormach will jog but all other commands need the machine home , which leads me to believe that portions of the command have been chopped . It's only a matter of figuring out where
    The only problem that the no force home causes is that the soft limits are lost but thats no worry since the hard switches are still recognized



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