GlossaryKind of term: Manufacturing termPocket
What is a pocket?
A pocket is a milled cavity bounded by walls and a floor, whose depth and internal corner radius steer the choice of cutter.
It is milled out of solid material and can be closed, with walls all round, or open on one or more sides. It can contain islands. Its vertical internal corners have a radius, because a cutter is round; the transition from wall to floor follows the corner radius of the cutter, nearly sharp with a square end mill, rounded with a bull-nose cutter.
What does a pocket depend on?
Time and approach depend on the volume to remove, the depth relative to the smallest internal radius, wall thickness, material and the stiffness of part and machine. The smallest internal radius limits the cutter diameter for the corners; the cutter radius is often chosen a little smaller than the corner radius, so the cutter does not wrap the full corner and is less prone to chatter. A deep pocket with a small radius needs a long, slender cutter with a long overhang and light cuts. Roughing often runs with a larger cutter on constant-engagement toolpaths, finishing with a smaller one.
How does a pocket work in practice?
With thin walls or a thin floor the part can chatter or distort, which shapes the cutting data and the order of roughing and finishing. A small corner radius in a deep pocket can be a large time item for the feature; a slightly larger radius may allow a stiffer cutter. Whether the designer accepts that depends on the function; when the radius drives the time, it is worth asking.
What is a pocket often confused with?
A pocket is not a slot: a slot is long and narrow, with a width often set by the cutter. Nor is a pocket a hole: a hole is round and comes from a drill or a boring bar, a pocket has a free contour.
Frequently asked questions
Can a pocket have a sharp internal corner?
Not by milling: the cutter leaves its own radius. A sharp corner needs sinker EDM, wire EDM for a through cut-out, broaching the corner, a corner relief or a design change. Ask which radius is acceptable before planning a very small cutter.
Which corner radius is favourable?
One that allows a stiff cutter at the depth asked. The larger the radius relative to the depth, the shorter and thicker the cutter can be. A small radius in a deep pocket means light cuts, and that takes time.