CNC Milling Operations
Milling uses rotating multi-point cutting tools to remove material. The primary variables are spindle speed (RPM), feed rate (IPM/mm per min), axial depth of cut (ADOC), and radial depth of cut (RDOC).
Climb vs Conventional Milling
In modern CNC setups with ballscrews (zero backlash), climb milling (down milling) is preferred for >90% of roughing and finishing passes. The cutter bites into the material at maximum chip thickness, reducing heat friction and directing chips behind the tool.
| Metric | Climb Milling | Conventional Milling |
|---|---|---|
| Chip Thickness | Starts Max, ends zero | Starts zero, ends Max |
| Tool Deflection | Pushes part into fixture | Pulls part up |
| Surface Finish | Superior | Poor (rubbing) |
Tool Engagement Angle
The engagement angle determines how much of the tool circumference is cutting. For high-speed machining (HSM) toolpaths (e.g., Mastercam Dynamic Milling or Fusion 360 Adaptive), maintaining a constant tool engagement angle (usually 10-15% RDOC) allows for full-flute ADOC and massively increased feed rates while preventing tool breakage.
Next Step: Calculate Feeds
Before writing your G-code, determine your baseline speeds. Use the Feed Rate Calculator →