Setup for squaring twin X-axis gantry

[JAZZCNC]

Can anyone tell me which of these options is required - I was expecting to get the switch pretty close mechanically and then fine tune the amount of back-off in software to get it dead on.

Take the time to Get it dead on to start with then you won't have to is the best option.!! . .. . .Then if any adjustments are needed at all your into fractions of millimeters and so just tweaking the switch is plenty.

Proximity switches are great for this has you have adjustment via the threads on the switch and altering the sensing distance if needed has well as any lateral adjustment you build into the switch.

[EddyCurrent]

I can't get my head round the fact that accuracy of the machine is down to the position and sensitivity of proximity sensors or switches.
I'm talking about repeatability I suppose, it's not so bad when there is one switch per axis but when there is a separate one for slaved motors it makes even less sense.
This is one area where absolute encoders are far superior and there are programmable limit switches based upon encoders but quite expensive.

[JAZZCNC]

I can't get my head round the fact that accuracy of the machine is down to the position and sensitivity of proximity sensors or switches.
I'm talking about repeatability I suppose, it's not so bad when there is one switch per axis but when there is a separate one for slaved motors it makes even less sense.
This is one area where absolute encoders are far superior and there are programmable limit switches based upon encoders but quite expensive.

Yep I agree 100% and exactly why I prefer screws connected Via belts has it's simple and accurate.! ...............Again thou it's down to usage and for machines which don't require higher accuracy or repeatabilty like routers just cutting wood, plastics etc then slaved motors are perfectly fine provided they are run within safe limits.

Edit: Daft as this may sound then if you want better accuracy from slaved motors than using switches just use Hard stops and slowly drive upto them before setting Zero.!