we're all worried about breaking the probes.

ok, standard probe design and tip... but the probe body's shaft that goes into collet... on end that goes into probe body install a round magnet, that the shaft will sit on (slightly recessed).

This way in an over travel situation the body will break away from the shaft.

No need to design the probe tip to break off.

Patent that idea

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Very good suggestion and really great for X and Y probing moves but it may be a different story for a -Z overtravel. 

Tweakie.

Tried that (;-) The Headshaft HAS have a slight recess where it goes on the headshaft and use a very strong super magnet on the tip. The trick is to keep everything straight and inline. Not as easy as it seemed. Also there was MORE force at the attachment contact point then I had imagined (;-)

The best approach is to have a set of double switches on the swaggle plate that the tip attaches to. The overtravel side runs through the limits circuit and will trip IF any  movement in XYorZ goes overtravel.

Just a thought(;-) TP