Limit switch problem

[ECCO]

First of all many thanks for your prompt replies. The idea is to have a lower Z axis limit switch that is easily and quickly adjustable, more for safety reasons than anything. This would mean having both upper and a lower limit switches fitted to the Z axis whilst having a single limit switch on both the Y and X and using soft limits set in MACH3. Do you think that this setup is possible?

[Clive S]

First of all many thanks for your prompt replies. The idea is to have a lower Z axis limit switch that is easily and quickly adjustable, more for safety reasons than anything. This would mean having both upper and a lower limit switches fitted to the Z axis whilst having a single limit switch on both the Y and X and using soft limits set in MACH3. Do you think that this setup is possible?

Possible but not practicable As Dean (Jazzcnc) has pointed there is no point in a -ve limit switch as you would have to adjust it every time you changed a tool etc.
.
Regarding the single limit switches and using soft limits in my opinion that would be a dangerous way to go as the soft limits would only work after you have homed the machine also if you stalled a motor the soft limits would not be correct in that the DRO would then be false.
.
If you only want to use one switch on X and Y then make it traveling with a target at each end.

[JAZZCNC]

Clive is spot on correct regards limits and soft limits it's a dangerorus combination really best avoided which isn't difficult to do.

Regards the Z aixs lower limit then he's not quite correct but still he's right. You won't have to move the switch every time you change tool etc if just protecting the extents of travel but it's mostly pointless because your never likely to hit the switch because you'll have tool in the spindle and material on the bed 99% of the time.
It's also got high potential for trouble from false trips etc because of all the vibrations and debris that get inflicted on Z axis down low.

Better solution is to fit hard stops so the rails bottom and motors stall if for some reason you ever get anywhere near the travel extents. Which is unlikely if your cutting and have anything but really thin material on the bed.

But to answer both your questions of is it do-able then yes it is. Would I advise it 100% NO.

[komatias]

Building on Jazz's note, you can have one switch per axis as long as it is actuated both in both the + and the - direction. But you must have both directions protected! As I said above, the soft limits are only there as a means secondary safety and only work if your machine has homed (Like Clive says)

here is a photo from practicalmachinist forum showing a single roller switch that is actuated by rolls that mount to the face of the table: