For safety reasons don't use a toggle switch for the 'start' switch on the 24v supply to relay 1. It must be a momentary push to make to enable both relays and use a contact on relay 2 to lock it in, as I drew it.

Why? your machine hits a limit switch, triggering estop (or you hit estop). everything turns off. You turn off the power at the main isolator but in your desire to see what happened you forget to turn off the 'start' switch. You reset the estop, or move the machine off the limit switch and turn on the main isolator... but the start switch is still closed so the 70v rail comes up and the machine starts moving again because you forgot to stop the PC...

Its a safety interlock, it mustn't remain in an ON position. Also you don't need both contact on Relay 2 to drive Relay 1, only one side of the coil needs to be switched.