Pocket

A pocket clears everything inside closed contours, down to the end depth, leaving islands standing. Select the contours, then Pocket (ribbon, OPERATION).

What gets cleared

• Each selected outline is its own pocket. Two that cross are cleared separately and never merged: the second cuts air where they overlap.
• Islands: a selected contour wholly inside a pocket is left standing. A contour inside an island is a pocket again.
• Not selected, not counted: contours that aren’t selected don’t matter, even inside a pocket. A circle you’ll drill later doesn’t become an island.
• Same shape twice: two selected contours that are the same shape are refused, since one can’t be both outline and island.

Rings

The pocket is cleared in rings:

• Order: rings are offsets of the walls, cut from the centre outwards, with the wall ring last at each depth. Round islands, each island’s rings are cut one after another, out to the island, before the next island’s, so the tool doesn’t cross the pocket between rings. Where an island is close to the wall (less than a tool diameter), its rings and the wall’s take turns there, so no ring meets more than a stepover of material.
• Stepover: the distance between rings, as a fraction of the tool diameter (0.4 by default).
• Rounded inner rings: every ring but the wall ring has rounded corners (up to two stepovers in radius), for smoother, faster motion. Where rounding would leave material, the corners are rounded less.
• Spiral: each ring steps out onto the next over its last stretch instead of closing, so the rings of a lobe are one continuous spiral with no stop and no sideways move into material. Round an island, its rings spiral out towards it the same way. The stepped-out stretch is checked against the walls and islands like a ring; where it wouldn’t fit (against a sharp corner, or onto a ring with a lead or a chosen start) the ring closes and is linked.
• Links: where a ring closes, the tool feeds across to the next at depth when the move stays clear of the walls and is at most one tool diameter, which it checks; otherwise it retracts. There is nothing to set: a checked link is always better than a retract.

What a round tool leaves is normal: inside corners keep the tool’s radius, and slots narrower than the tool stay uncut. The simulation shows it. Chipload also warns about two things:

• Uncut material: the rings don’t pass close enough to some material (a stepover too large for the shape). Lower the stepover.
• A narrow part: the tool doesn’t fit through a narrow part of the pocket. The pocket is cleared as separate areas, and material stays in between; a rest pass with a smaller tool can clear it.

Entry

• Plunge: straight down at the innermost ring. It needs a centre-cutting endmill.
• Ramp: down along the first ring, out and back, never steeper than the ramp angle.
• Helix: down round a small circle at the pocket’s widest point, as helical G2/G3.
  • The radius is a quarter of the tool diameter by default, and must be less than the tool radius. Where there’s no room, it shrinks.
  • With no room for even a tenth of the tool’s diameter, the pocket ramps in, with a note.
  • New pockets use a helix when the tool is marked not centre-cutting.

Start point and lead

As on profiles: drag the start marker of each wall ring, and add a lead from the cleared side onto the wall.

Dogbones

Corners puts dogbones or T-bones into the pocket wall’s inside corners, as on profiles, and any corner can have its own choice (corner by corner). Not with rest machining.

Rest machining

A pocket can have rest passes: smaller tools that clear only what its tool left, shown under it in the Browser. See Rest machining.

In the file

"type": "pocket" in the project file. Lengths are in mm, feeds in mm/min, angles in radians.

Projects from before Chipload 0.14 that used the removed trochoidal or adaptive clearing are cut as ring pockets. Projects from before 0.18 that had the tool retracting between rings or sharp inner rings now get links and rounded rings: the same rings, cut faster.