Knock yourself out building the best motor disconnect the world has ever seen. Still a bad idea, but I guess you want to figure that out on your own.
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There is no education on the planet had without some form of tuition (time, money, blood, sweat, tears)âŚ
âŚNo? 
True True, but sometimes listening to the advice of others can help lower that tuitionâŚ
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Fair enoughâŚ
...Sometimes we simply learn best in certain styles. Like anyone, all that I can do is gather all of the information available, weigh the pros and cons along the planning & investigation stage, and jump out of the door on the green light. LOLI am not running grbl anymore as I switched to the gecko g540 and mach3, but I have a switch on my control box that disengages the motors allowing me to move things around without powering anything offâŚthat being said, I have never used itâŚI always just jog with the software.
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Did that switch come with the gecko, or home-built?
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I had my new controller professionally assembled. It is here:
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I think you are wasting your time and adding an un-necessary failure point. Imagine the damage to your machine if the connection to one stepper (especially a Y stepper) failed while the rest of them merrily carried on, twisting the machine into a pretzel!
Protection diodes in any good motor controller board handle any back EMF generated when you jog the machine by hand, so as long as your machine is powered off, doing so will not damage your controller.
My machine has been in use for over 18 months in a middle school shop and over 300 students have used it multiple times each. Hand jogging the machine is written into the setup procedure I have designed and there have been no problems. We do it 20 or 30 times daily.
All adjustments, except for final homing, are done with the machine powered down for safety. The DeWalt 611 spindle and the power supply and motor controller are all powered from a modified IoT relay. The spindle is controlled by the relay, the controller and PS are powered from the âNormally ONâ side of the IoT relay, which has been modified to be an âAlways ONâ outlet, meaning that it is no longer switched by the relay, but is still controlled by the IoTâs main power switch and protected by its surge circuit.
At the end of a carve the students power down the IoT, raise the spindle with a hand wheel I have added to the z-axis screw, and push the gantry back out of the way before removing their workpiece. They then clean and vacuum the machine, and help the next student with setup. All movement of the machine is done manually until final homing. Keeping it powered down during setup reduces danger, and having the kids manually manipulate the machine gives them a better understanding of the mechanics and mathematics of the machine.
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