Tool overhang is distance from tool base point to tooling point.
Tool base point is base point of instrument block ( tool and tool holder) at machine coordinate system.
For mill machine tooling point lie along tool axis.
Some overhang definitions for mill machines are shows below.
Tool base point
Axial tool overhang
Overhang for rotary head
Overhang for 2 rotary heads
For lathe machines base point lie on turret base plane along tool fix system axis.
Some overhang definitions for mill-lathe machines are shows below.
Base tool point on turret
Straight turning tool overhang
Boring bit overhang
Base point for radial milling head
Base point for axial mill head