Thank you both , Gentlemen, for your honest and succinct answers. The z zero tool I have ordered from Aliexpress has a description of "Automatic Tool Sensor Mach3 Z Axis Probe NC Auto Zero Check Touch Plate for CNC Router Milling Engrave Machine", idea being as you both have indicated, being permanently fixed in x and Y with an automatic script running z height touch off prior to machining. The unit is about 65mm high, appears to have some kind of air solenoid to blow a puff of air across the top of the touch off plate, for what that's worth, possibly just a bit of Chinese bling. I will check out the link you have sent me, thank you.
On a second note, I posted a while back regarding probing of rifle stocks to bring into Alibre for clean up, machining strategy etc, utilising 4 axis. A fellow gave me some valuable information regarding depth blocking for z etc. I appear to have two probes in my stock, both unused and both at least 20 years old. Could I get confirmation, as far as we can see, that this probe will be able to do the job, also on Aliexpress."The Latest Upgrade V6 Anti-roll 3d Touch Probe Edge Finder Centering Desktop Cnc Probe Compatible With Mach3 And Grbl ", I do actually have a couple of lighter machines running GRBL, but it is Mach 3 I am interested in.
Thanks in advance, in Australia, we think of Americans during these troubled times and wish you all the best we possibly can.
Regards
Mark