What is your definition of Interlock, there is the Normal E-stop circuit which Every CNC machine should have, there is also a key lock-off.
The basic E_stop is simple to implement and should disconnect power to any motive power devices and hazardous sections.
http://static.schneider-electric.us/...0140CT9201.pdf
There are several examples there.
Do you have a circuit diagram of the machine? Also earthing is a consideration which Chinese machine are notorious for omitting.
Al.