Denford PCB Engraver User Manual page 24

5: Performing a Tool Change
Place the spindle motor back into the fl oating assembly.
Make sure the clamp is clean and free from debris. Retighten
the thumb screw.
Loosen the cap screw and adjust the fl oating ring by turning
until the tool tip protrudes...
The tool should protrude just enough to break the surface of
the engraving material or PCB. Now tighten the cap screw.
PCB Engraver Operator Manual
Page 24