One limit switch per axis

[EddyCurrent]

Just ignore, I seem to have posted twice.

[JAZZCNC]

The failure is usually caused by the switch never being used and then they stick down in the on position not the wire being broke ---------So when you release the machine off the switch it is stuck on the on position -so normally open would be a good idea ?

No that's unsafe and it's very common for a wire to break or come disconnected in which case the machine E-stops.
Doesn't matter if the switch is stuck after being tripped because E-stop is still affective it just means you have to find the faulty sticking switch which you would want to do anyway.

Regards the Limit over ride then I use Momentary button with Buzzer warning it's overridden.

[manofgresley]

Hi

Yes there's 2, but very easy to install

Something like this ?

Ray

[EddyCurrent]

If I was using servos and encoders I would be using the absolute type and as you say soft limits would be my choice with hard limits providing final limits. As I'm using stepper motors this is not an option so while I could fit encoders I've decided to just fit switches. As you say, once these switches have been activated there must be a way to recover and I admit I have not investigated this aspect yet but I'm sure there is a simple solution such as an override button as you mention. With regard to limit switches these are always in the normally closed mode and are opened upon activation, this means that if the wire is broken or the connection fails the system will stop.

[Ulsterman]

Removed by me

[irving2008]

All safety systems, and limit switches are just that, should ALWAYS fail safe. This means that a failure if the wiring or of a connector MUST result in a fail condition. Being stuck in e-stop nay be inconvenient but no system should ever be designed that cannot validate that it's safety mechanisms are working therefore continuity of limit switches and their wiring is a fundamental pre-run test. It's also why e-stop and limit switches should interlock directly on motor power and not rely on software intervention. You should ALWAYS require some manual action to over-ride e-stop or limit switches, usually by holding down a momentary contact switch while cycling power or performing a software reset action.