GlossaryKind of term: Manufacturing termTrochoidal milling
What is trochoidal milling?
Trochoidal milling cuts slots and pockets in small circular loops, with a narrow radial width of cut and a large axial depth of cut.
In trochoidal milling the cutter follows a path of loops: a circular motion that steps forward a little with each loop. The cutter is smaller than the slot or pocket. The radial width of cut ae is small relative to the diameter, and the axial depth ap can be a large part of the flute length. The cutter therefore engages over a short arc per revolution, and wear spreads along the full flute length.
What decides whether trochoidal milling works?
When the radial width is less than half the cutter diameter, the maximum chip thickness is smaller than the feed per tooth; this effect is called chip thinning. To keep a workable chip thickness you raise the feed per tooth. The short engagement gives the edge more time to cool on each revolution and lowers the radial force, which limits chatter in deep slots. Whether it works depends on the cutter (number of flutes, chip space), chip evacuation from the slot, the material and the machine's dynamics: in small loops the axes accelerate and decelerate constantly, and acceleration limits and limited look-ahead in the control often keep the machine below the programmed feed.
How does trochoidal milling work in practice?
A rule of thumb from full-width slotting does not give a usable time here. The path is much longer, but runs at a higher feed and a greater depth, so per slot the time can come out shorter or longer. An estimate from path length and programmed feed often comes out too low when the machine slows down in the loops. What you usually gain in return is longer tool life, less risk of a broken cutter and one cutter for slots of different widths, as long as the slot is clearly wider than the cutter. The method is common in stainless steel, titanium, nickel alloys and hardened steel, and is also used in plain steel and aluminium.
What is trochoidal milling often confused with?
Trochoidal milling is not high-speed machining: HSM is about high spindle speeds and cutting speeds, trochoidal milling about the shape of the path and a light engagement. The two can go together, but one does not require the other. Nor is it helical ramping: that is the helical move a cutter uses to reach depth. And not every toolpath with a limited engagement angle, as CAM packages offer under their own names, is trochoidal: those paths often follow the shape of the pocket and need not loop.
Frequently asked questions
When should you use trochoidal milling?
For slots and pockets in tough or hard material, such as stainless steel, titanium and hardened steel, and for deep slots where a full-width cut would chatter or pack with chips. In shallow slots in free-machining material, conventional slotting may be enough.
Is trochoidal milling faster than conventional milling?
Not by itself. The path is longer, the feed higher and the depth greater; per slot it can take more or less time, and the machine's dynamics play a part. The benefit usually lies in tool life and process stability.