The ZAY7045 I have has an interesting "feature".

Normal operation:

• To start: Re-arm the "E-STOP", switch it to "Drilling/Milling" and press the "Start" button (spindle turns clockwise)
• To stop: Switch it to "Stop" or press the "E-STOP" (spindle stops)
• To restart: Re-switch to "Drilling/Milling" and/or re-arm the "E-STOP", and then press the "Start" button again (seems a little redundant).

Tapping:

• To start: Switch it to "Tapping" and press the "Start" button (spindle turns clockwise).
• To reverse out: Lower the quill until it triggers the bottom switch (spindle suddenly turns counter-clockwise).
• To stop: Raise the quill until it triggers the top switch (spindle stops).
• To restart: Press the "Start" button (spindle turns clockwise).

I can see that if you were tapping at the same Z height all day, that this could be a handy option. But the setup to get the quill switch to engage at the right point would be far too fiddly for small jobs.

This is achieved with 1 switch (SPDT centre off), 2 micro-switches (SPDT), 2 buttons (1 NO & 1 NC) and 2 relays (with 5 NO & 1 NC each).

So, what's wrong with current controls?

• The tapping feature was of little use, and will be of less with the CNC conversion.
• The spindle start is onerous, requiring switching and start button.
• Spindle stop is uncomfortable (flicking around a flimsy switch).
• It didn't allow a manual way to start the spindle counter clockwise.
• The E-STOP doesn't stop CNC servo movement.
• The spindle doesn't start and stop under CNC control.

What's the answer?

• Change the spindle switch to CNC-Off-On
• Create a new independent E-STOP line that cuts power to the spindle and servos, and informs the PC on E-STOP button or axis limits.