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Bug in 1.6 onwards...

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  • Art
    Hi All: An un-noticed bug in the feedrate code has been found by one user (Thanks Robin) which can create great problems for plasma users. A semi-circle will
    Message 1 of 3 , Oct 31, 2003
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      Hi All:

      An un-noticed bug in the feedrate code has been found by one user (Thanks
      Robin) which can create great problems for plasma users. A semi-circle will
      not go at full rate speed, it will only run at the maximum feedrate of the
      slowest axis on the machine when a semi-circle is made. The code has been
      corrected for the next release. It was sensing a movement of 0 units, which
      clicks in a special safety code which sets the feedrate of such a move to
      the slowest axis for safety considerations, while invisable most of the
      time, it bit me when correcting the offset code in 1.5 or so.

      Sorry for the bug, just a word to the wise...

      PS: Robin has questions as to how the tool tip can be made to retract on
      contact. Can one of you plasma heads tell him how you do it....(Isn't this
      done on a spring loaded plate or something..Or does it use the G32
      command?..

      Thanks,
      Art
      www.artofcnc.ca
    • Les Newell
      If it is a drag cut torch then the simplest method is to use a solenoid controlled by the Z axis direction pin. Setting the Z axis depth and feedrate controls
      Message 2 of 3 , Nov 1, 2003
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        If it is a drag cut torch then the simplest method is to use a solenoid
        controlled by the Z axis direction pin. Setting the Z axis depth and
        feedrate controls the dwell time.
        My setup uses the following logic: If spindle is on and Z direction is down
        then turn on the cutter.
        I then use a window comparator to monitor the torch voltage so that the
        solenoid only comes on when the torch is lit. The main reason I did that is
        because my torch won't light reliably if it is touching the work.

        Les

        >
        > PS: Robin has questions as to how the tool tip can be made to retract on
        > contact. Can one of you plasma heads tell him how you do it....(Isn't this
        > done on a spring loaded plate or something..Or does it use the G32
        > command?..
        >
        > Thanks,
        > Art
        > www.artofcnc.ca
        >
      • Robin Szemeti
        Thanks for the quick bug fix Art, I ran it up on the table and its just fine .. nice and smooth too. ... Ok, I use a proper machine torch and the arc_good
        Message 3 of 3 , Nov 1, 2003
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          Thanks for the quick bug fix Art, I ran it up on the table and its just fine
          .. nice and smooth too.

          On Saturday 01 November 2003 11:41, Les Newell wrote:
          > If it is a drag cut torch then the simplest method is to use a solenoid
          > controlled by the Z axis direction pin. Setting the Z axis depth and
          > feedrate controls the dwell time.
          > My setup uses the following logic: If spindle is on and Z direction is
          > down then turn on the cutter.
          > I then use a window comparator to monitor the torch voltage so that the
          > solenoid only comes on when the torch is lit. The main reason I did that is
          > because my torch won't light reliably if it is touching the work.

          Ok, I use a proper machine torch and the arc_good signal comes straight out
          of the CNC interface on the plasma so no worries there ... lighting up with
          the torch touching the work is a sure-fire way to blow nozzles. its only the
          airflow spining down the nozzles that stops the arc eating it for lunch.

          And I am going to use the THC logic in mach2 to drive the Z servo .. I know
          how to do the mechanics with a spring loaded plate and microswitch to detect
          the material .. I just cant figure out how to interface it to Mach2

          the two bits I need are:

          where do I tell mach2 to do the Z axis down, detect stwitch and then retract
          before lighting the plasma? .. where is this set? I'm using M3 as my torch
          on, Do I have to write a macro for M3?

          How do I tell Mach2 to wait for the Arc_is_good signal before commecing
          motion?

          Are people using the spindle pin for plasma_on output signal? which pins do
          I need to use for the THC up/down signals???


          in short my required procedure is:

          M3:
          lower Z until touch switch activates
          retract Xmm (where X is pierce height plus switch throw distance)
          plasma_on pin goes high
          wait for arc_good input to go high
          wait for pierce delay (this can be set on the plasma itself.. not essential
          to do it in the code)
          commence motion
          enable THC servo inputs


          M5:
          thc servo disabled
          plasma_on goes low
          Z retract to safe height
          motion continue

          from my reading of the manual I thought someting like this was already
          incorporated into Mach2 .. but maybe it was done with (private) macros?? or
          added to the GCODE? .. i prefer not to put it in the GCODE, leaving that as
          clean as possible. If it is done with hand written macros, I'll have a go at
          those myself, just dont want to duplicate work.

          in an ideal world the THC servo would hold whenever the actuall speed was
          less than say 50% of the desired speed

          --
          Redpoint Consulting Limited

          Real Solutions for a Virtual World
          http://www.redpoint.org.uk
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