Constant engagement, and why it lets you cut deeper

Radial engagement is the fraction of the cutter's diameter that is buried in material at a given moment. It is the number that decides how much force the tool takes, how much heat goes into the edge, and how loud the cut is. Almost every feed and speed you have ever been given assumes a particular engagement and quietly falls apart when the real one differs.

Where offset paths go wrong

A concentric offset pocket keeps a constant stepover — the distance between one loop and the next — which is not the same thing as constant engagement. On a straight run, a 40% stepover really is about 40% engagement. Turn into an inside corner and the cutter meets material on two sides at once: the engagement spikes, briefly approaching full width.

So the feed you chose has to be the feed that survives the corner, not the feed the straight runs could have used. In practice that means a shallow depth of cut and a conservative feed everywhere, to protect the tool for the fraction of the path where it is actually in trouble.

What adaptive does instead

Adaptive clearing computes the path so that engagement stays near a target you set — the optimal load — rather than the spacing staying constant. Corners are rolled rather than turned, the path arcs away and back rather than driving into a concave corner, and where the geometry cannot be smoothed the strategy inserts a small relief loop so the tool unloads before it re-enters.

Because the worst case is now close to the average case, the trade you make is a different one: engagement drops (often to 10–20% of the diameter) and depth of cut rises to most of the flute length. The cutter takes a thin, tall slice instead of a wide, shallow one.

Why that is better for the tool

• Heat is spread along the whole flute length instead of concentrating in the bottom two millimetres, which is where end mills usually die.
• Chip thinning at low engagement lets the feed per tooth go up rather than down — a light radial cut wants a faster feed, not a slower one.
• The cutting force is steadier, so the finish is more even and the machine's own flex stops modulating the surface.
• A smaller machine with a light spindle can take a deep adaptive cut it could never take as a full-width slot.

When not to use it

Adaptive earns its keep on volume. A shallow pocket only a couple of millimetres deep gives it nothing to trade — the depth is already the constraint, and a plain offset or raster clear will do the job in fewer moves. Very small pockets are similar: if the pocket is barely wider than the tool, the path has nowhere to roll and you are cutting a slot whatever it is called.

In Carvect the target is the optimal load on the 2D Adaptive form, expressed as a fraction of tool diameter. Corner relief loops are the trochoidal corners option; their size is a multiple of the same stepover.