Hi Bob,

Chances are that Mach is set to "Ignore tool change" like as been mentioned. Change it to "Stop Spindle wait for cycle start" not to "Auto tool changer"

Then what happens is that the motion stops at last commanded position before the M6 command then the spindle will stop. You can then Jog away to any place you like to change the tool. Then jog back and reset new Z height for new tool length. After set Z height push cycle start and the spindle will restart and motion will resume at next commanded position.

If you want to machine to move to a tool change location then the M6 start macro will need to be modified.