Travel to fixed stop function on various CNC controls
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    Default Travel to fixed stop function on various CNC controls

    Hi,

    On machines with Siemens 840D control i often use the function "Travel to fixed stop" (FXS on Siemens) to do tasks like rough measuring without probe, gently pushing workpiece to seat against a fixed stop while the chuck is being unclamped/clamped, and when using the tailstock with lower pressure than the hydraulic quill allows.

    I am looking to do the same on machines with Fanuc and Mazak controls, but can't seem to find anything when searching through the manuals. Is this not a common feature for controls other than Siemens?


    The function is described like this is the Siemens manuals:

    The function of “Travel to fixed stop” can be used to move a motor to a fixed stop at
    a specified torque without a fault being signaled. When the stop is reached, the
    specified torque is built up and remains applied.

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    You can do it on Mitsubishi Meldas M700 controllers on Citizen lathes. That's my only experience with it.

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    Mazak has a PUSH option somewhere in the TRANSFER section. For transferring from main to sub spindle. Used to press a part against a step jaw.

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    If you can find a DMG-Mori manual for an NL or NLX, then you should find the information you need for both, a Mits and a Fanuc control.
    However, not sure how much of a help that will be as it is an MTB defined M-code function.

    The answer though is yes, Fanuc and Mits can do it as well.

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    On a Fanuc, the option is called "Torque Skip". We have it standard on all of our Doosans with sub-spindles. It aids in part transfers mostly. G31 P99 with an axis move, usually Z, will cancel the remainder of the move when a axis load value reaches a certain amount.

    Paul

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    Quote Originally Posted by LockNut View Post
    On a Fanuc, the option is called "Torque Skip". We have it standard on all of our Doosans with sub-spindles. It aids in part transfers mostly. G31 P99 with an axis move, usually Z, will cancel the remainder of the move when a axis load value reaches a certain amount.

    Paul
    Used with some conditional statements and reading the machine position, it makes a pretty good poor man's probe.

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    Quote Originally Posted by TeachMePlease View Post
    Used with some conditional statements and reading the machine position, it makes a pretty good poor man's probe.

    Yes it does! Macro B is the BOMB!

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    I've always thought that Torque Skip would be handy to stop the machine if the material blank was too long. Turn on a torque limit then G31 P99 X-.06. If the torque limit was exceeded it would skip the remaining cut and would branch to the end of the program with a macro alarm (#3000).

    Maybe a way to avoid pushing a blank out of the chuck. Never had a chance to play with it though.

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    Thanks everyone for your input, I appreciate it!

    I checked out Fanuc's Torque Skip function and although it looks a bit more limited than Siemens FXS command it can be used for many similar tasks.
    I will also look into PUSH function on Mazak.

    With Siemens FSX, the programmed torque is built up when the axis reaches the fixed stop and remains applied until it is canceled. If the fixed stop moves, the axis with active FSX will move with it to keep the torque constant. Basically simulating a spring. You can also change the torque limit any time, even during movement.

    As an example I use this on a part where we want a live center mounted on the lower turret to just barely rest against the part. I want to use a torque limit that is lower than what is needed to start axis movement because of stick slip. The movement against the part is started with a torque limit big enough to move the axis, then it is lowered a bit just before it reaches the part.
    The length of the workpiece also grows a bit during machining, but the turret with the live center adjusts its position to keep the torque constant. If the FXS command was canceled right after it hit the part, what started as 6% axis torque would be maybe 10% at the end of the cycle.

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    Quote Originally Posted by Vancbiker View Post
    I've always thought that Torque Skip would be handy to stop the machine if the material blank was too long. Turn on a torque limit then G31 P99 X-.06. If the torque limit was exceeded it would skip the remaining cut and would branch to the end of the program with a macro alarm (#3000).

    Maybe a way to avoid pushing a blank out of the chuck. Never had a chance to play with it though.

    Torque skip will just move on to the next line of code. It could jump to an alarm if you want it to. Best use for that would be if you want it to sense too much stock left after facing. Maybe to check your insert if the position exceeds a certain tolerance and if not, just move to the next line of code.

    Paul


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