Spindle on/off under CNC software control - safety worries!

[JAZZCNC]

So how is this addressed in practice? (I'm sure it's not just me that it alarms!) ...the thought of a simple relay to control the spindle on/off doesn't seem that robust....I'm figuring there needs to be some form of time delay (sustained condition for X seconds) before the spindle can be allowed to start?

Doesn't work like that Hank. Works in 2 ways.?

If doing a tool changes in Job then the M6 tool change macro code stops the G-code and the spindle via switching the relevant output state controlling the spindle relay. It then waits until you press cycle start again often pausing for a second or two so the spindle spins upto speed before continuing on thru the g-code. It's not a time based operation at all.

OR. . . You can manually stop/start the spindle often Via a screen button or thru MDI using M3/M5 G-codes which does the same has screen button and switchs the relay with it's output signal.

If you really don't trust the relay or system then just do like M-C says and put an in-line isolator switch. Doesn't need to be on power lines it can be a simple on/off switch breaking the signal to relay so the NO relay can't be switch state.!

In practice it's not a problem and I've never had a false start or relay switch state.