Trochoidal Milling
Trochoidal milling is a high-efficiency CNC roughing strategy that removes material using a continuous looping or spiral toolpath, maintaining low and controlled radial cutter engagement. It is commonly applied for machining slots wider than the cutter, pockets, and hard materials.
On the shop floor, trochoidal milling is employed when a conventional full-width slot cut would overload the cutter, cause excessive heat, or induce chatter in the part. The CAM generates overlapping circular arcs, keeping the tool in constant motion and avoiding heavy full-width bites. The technique typically uses a low radial depth of cut (RDOC) combined with a high axial depth of cut (ADOC), which reduces cutting forces while enabling aggressive material removal in depth. This is particularly useful for pockets, grooves, deep slots, mold and die work, and difficult-to-machine alloys like stainless steel and superalloys, where chip evacuation and tool heat are major limiting factors. The practical cutting benefits include a more stable chip load, less heat buildup, reduced vibration, and the ability to run higher feeds and speeds compared to conventional slotting, provided the machine rigidity and tooling support it.
- Too much radial engagement: Increasing stepover beyond trochoidal range turns the tool into a conventional slot drill, sharply raising cutting force and heat, risking tool breakage and part tolerance loss.
- Wrong feed per tooth after engagement change: Keeping conservative slot feeds with trochoidal path causes tool rubbing, worsening work hardening in stainless, shortening tool life, and leaving poor floor finish.
- Poor chip evacuation in deep pockets: If flute length, coolant, or chip clearing is insufficient, chips recut in the looping path, leading to edge chipping, built-up edge, and rapid wear despite light engagement.
What is the defining geometric feature of trochoidal milling?
A trochoidal or looping circular path with simultaneous forward motion that creates repeated partial engagements rather than a straight full-width slot cut.
Why does trochoidal milling reduce tool load?
Because the cutter maintains a small, controlled arc of contact and avoids burying the full diameter in the cut, which lowers instantaneous force and heat.
Why is trochoidal milling favored for difficult materials?
Difficult-to-machine alloys benefit from the lower force, lower heat, and better chip evacuation characteristic of trochoidal motion, especially in deep slots and pockets.