In article ,
Ignoramus31989 wrote:

Just wanted to do a little sanity check.

The question is about wiring power for all motive power (XYZ and
spindle) on this Bridgeport CNC mill.

The mill will be wired for single phase, with spindle motor on a VFD.

My current plan is as follows.

1. The CNC PC would be fed with incoming power without ANY regard for
any switches. When I need to shut it down I would type "sudo shutdown". I
will use this PC for many other shop purposes.

2. Have a switch (original switch on the door) be the first control of
incoming power to the mill (besides the PC, see 1)

3. Have all incoming power go through two fuses.

4. Jon's PPMC control box will be powered by 220v (more like 243 VAC
in reality). So any one fuse that blows, would cut the power to PPMC
control box.

5. Servo power supply, as well as power to the spindle VFD, will be
provided through a contactor.

6. Regular start and stop buttons would simply send signals to
software via PPMC.

7. The motive power contactor is actuated by a solid state relay built
into PPMC, but its control line will also go through a relay
controlled by estops, so that pressing ESTOP automatically cuts all
power to any moving equipment. I may need an extra relay in the estop
circuit, so that ESTOP not only cuts off motive power, but also sends
a signal to the control box and thus to the software that estop
occurred.

What I like about this approach is that it is relatively idiot proof
(estop means stop regardless of any software mistakes), and yet by
preserving power going into PPMC, I can keep track of my position
etc. It also keeps the PC going.

The minus is that in case of estop, the motors will coast to stop
instead of braking. But it is more simple.

Does this make any sense?

In addition to all the good points made by others, I would add one thing:
Ensure that if prime power is lost and later regained, all motion will stop and
stay stopped until you give permission.

I would also go through your design and ask the question for each and every
component: what happens if this fails (stuck on, stuck off, or stuck open)? I
particularly liked the part about busted encoders breaking machines as the
servos manfully tried to achieve the unachievable.

Joe Gwinn