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  1. #21
    ericks's Avatar
    Lives in ALDINGA BEACH, Australia. Last Activity: 11 Hours Ago Has been a member for 0-1 years. Has a total post count of 25. Received thanks 2 times, giving thanks to others 0 times.
    Using a field isolator on drive driven motors are an Industry standard. They are lockable isolators.....obviously you would isolate after you have "stopped" the motor:)

  2. #22
    Quote Originally Posted by Kitwn View Post
    Connecting/dissconnecting a motor from a VFD or stepper controller when it is powered is generally considered a risky business due to the voltage spikes that can occur. Power transistors have been described as 'the fastest fuse on three legs' for good reason. If your switch has a back contact that can be used to prevent the VFD from trying to start when the motor is not connected that might be a good move.
    Perhaps I was not clear, it is NOT meant to be on/off switch, just safety switch to make sure the spindle will NEVER be started by accident or error while there is a tool change in progress. Of course, the spindle is not spinning when the switch is flipped to off, and the VFD is not feeding the motor power outputs when the switch is flipped to on. Starting and stopping the motor is of course done by the CNC software, in my case through Modbus commands.

    Power transistors provide ZERO safety, quite the opposite, they give you a false sense of safety and may not operate when needed. A mechanical switch will always work because it is just what it is, simple and 100% independent from electronics and software/firmware.

  3. #23
    This is like a health and safety thread on a model engineering site! ;-)

    Commercial CNC machines rely on the spindle motor drive, with a suitable signal from the controller, to prevent the spindle starting up whilst changing tools, that works, failure to understand why will lead you to think you need breakers and stuff between the motor & VFD when you don't.

    If you have a decent VFD it has the facility for an E-Stop data input, this will suffice on equipment of a reasonable quality.
    You think that's too expensive? You're not a Model Engineer are you? :D

  4. #24
    A-Camera,
    I appreciate that a proper procedure for stopping and isolation protects the VFD. My concern would be the occasional operator error, possibly starting the VFD before closing the contactor which is why I suggested the back-contact interlock to prevent the VFD from operating with the contactor open. This ties in with my earlier comments about the 8 second delay etc. These spindles are a big investment for a hobbyist and anything you can reasonably do to prevent one of those potentially expensive "Oooops!" moments is worth considering.
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

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