kvnnos,
I suspect you know this already, but in case you don't. At a very minimum, your E-Stop should be
hard wired to drop all your outputs. If you have air cylinders they should vent on e-stop to De-energize the system. Usually on CNC machines, you have a dual chain e-stop, if you really want to Cadillac put in a safety relay. A CAT 2 type circuit is usually good enough for a CNC machine, but you will need CAT 4 if you have a press or robot (with monitoring), in the U.S. Don't know about the EU or others...... You can't use a software E-Stop (slight caviot within this last year is some of the "Safety PLC's", that claim they meet the OSHA/NFPA requirements...... wouldn't want to test that liability as of yet). Really your E-Stop circuit (accessory N/C swicth), just notifies Mach that an E-Stop has happened.
IF you machine is large enough to warrant a safety relay, or you have employees running your machine, here are a few choices for an Safety relay, from cheap to expensive, but all do about the same job.
This assumes your machine does not have light curtains (would be very rare on a CNC machine).
the minimum spec on a CAT 4 would be dual chain with monitoring feed back.
(i.e. E-Stop(s) and Door Switch(s) To go with this, you would need, 2 "Force Guided Relays".
that supply the "Switched" hot for the 24v commons on your outputs from your PLC or what ever.
1). Dold Safety Relay from Automation Direct.
2). Omeron Safety Relay.
3). Allen Bradley Safety Relay.
Scott