Depth Of Cut

Depth of cut in milling is the axial depth of cut (ADOC), also called stepdown or cut depth, representing the thickness of material removed in a single pass. It is programmed as Z-axis engagement from the uncut surface to the newly machined surface. In turning, depth of cut is the radial reduction in radius, calculated as (D_before - D_after) / 2.

On the shop floor, depth of cut determines how much stock is removed per layer and directly impacts cutting forces, tool deflection, chip load, cycle time, and surface finish. In woodworking and millwork, depth per pass is often limited by tool diameter, material density, spindle power, and flute length; a common rule for routers is not exceeding 3 4 times the tool diameter in a single pass, though actual safe values depend on machine rigidity and material. For pocketing, contouring, and 3D finishing, machinists use multiple stepdowns to reduce chatter, heat, and cutter breakage while improving dimensional control. Depth of cut is a key variable for material removal rate (MRR); increasing it raises MRR but also increases cutting load and the risk of poor finish or tool failure.

• ⚠️Overloading the cutter: Taking too deep a cut can cause the tool to dig in, chatter, or break, especially with slender end mills or long reach tooling; the machine may stall or lose accuracy under increased cutting force.
• ⚠️Ignoring tool stickout and flute length: Excessive depth relative to usable flute length forces chip recutting, poor evacuation, heat buildup, and rubbing rather than cutting, even if spindle power is adequate.
• ⚠️Confusing axial and radial engagement: Setting a safe stepdown but excessive stepover can still overload the tool; both axial and radial depths of cut affect force, chip thickness, and finish, so depth cannot be chosen in isolation.