TOS-KURIM CNC Upgrade

[m_c]

Officially all user buttons should be low voltage (IIRC in this context, it's sub 60V), which is why most control systems use 24VDC.

In an industrial setting, you would normally use a dedicated safety relay (essentially a relay with multiple contacts, that all get monitored, and should any fail, the relay won't activate).
However what happens when an E-stop gets pressed, is down to risk assessment. An E-stop should bring the machine to a stop in a safe and controlled manner. With modern servos, you would normally do that by triggering the servo drives fast stop input, then a few seconds later, remove drive power. This means the drive should bring the servo to a fast stop, then power down. If you simply cut power, the servo can keep moving then freewheel to an uncontrolled stop.

However, as it looks like you're using older DC servos, then you have to consider a servo runaway failure.
DC servos is one setup where I would seriously recommend where limit switches are part of the e-stop circuit, and the E-stop kills the drives as quickly as possible, as you really don't want a servo running past the limit switch under full power.