Part-in-part nesting: cutting small parts from the holes of large ones

When it pays

• Rings, flanges and frames: a large centre hole or cut-out is a slug of the same material and thickness, already paid for.
• Mixed jobs: washers, tabs and small brackets can fill the holes of the large parts instead of taking sheet of their own.
• Not when the customer wants the slug, or when it belongs to another job. CypNest has a “Forbid nest inside” option for this, and Hypertherm lists permitting or prohibiting nesting inside a part among the typical features of nesting software.
• Not when the small part would sit unsupported: see heat and tip-up below.

How big the hole must be

The rule is the same as between any two parts: the small part needs the full part spacing to the edge of the hole on every side. So the hole must be wider than the small part plus twice the spacing — with 3 mm, a Ø100 mm hole holds a part that fits inside a Ø94 mm circle; with 6 mm, a 200 × 150 mm cut-out holds a part up to 188 × 138 mm (examples). The kerf comes out of that gap too. Small holes in the small part are a question of their own: Zorocut's pre-cut check warns when a hole is smaller than the sheet's thickness, and minimum hole size covers the limits.

Cut order, heat and tip-up

1. The small part's holes.
2. The small part's outline: the part is now free, held only by what is left around it.
3. The large part's holes, including the one the small part sat in — its slug can now drop without taking an uncut part with it.
4. The large part's outline, last.

• Why this order: NestLib's sequencing documentation puts it plainly — you cut the inside part before the outside part. Zorocut's cut order does the same, and inside every part it cuts the holes before the outline, because a part cut free first can shift and its holes would land off.
• Tip-up: TRUMPF writes that parts or inner contours not resting on at least three support points tend to tilt, and that small parts up to 6 mm thick are most at risk. A small part cut free in the middle of a slug may rest on fewer slats than you think; micro-joints hold it — see micro-joints.
• Heat: many cuts in a small area heat the sheet, and NestLib warns that the warping that follows is dangerous for the laser. CypNest's sort has a Heat Dissipation option that cuts dense areas region by region, and a Smaller Figure Prior option that cuts small parts first.
• Room: CypNest has a Center Inner Parts command that spreads the parts in a hole evenly to prevent damage — the same idea as keeping the full spacing to the hole's edge.

In CypCut, CypNest, other nesters and Zorocut

• CypCut classes contours by how they nest (§3.1.1): the outermost is an outer contour, the next one in a hole, the next an outer contour again — so a part in a hole gets outer-contour lead-ins. CypCut also sorts on import (§1.4.2): step through the sequence preview (§3.15.1) and use manual or group sort if the small part does not come first.
• CypNest: “Nest inside first” places small parts in the cut-outs of larger ones before using the plate; “Forbid nest inside” keeps a part's slug whole.
• Other nesters: Hypertherm lists permitting or prohibiting nesting inside a part, cut direction and sequence set part by part, and an animated simulation of the cut order among the typical features of nesting software.
• Zorocut: the nester places parts in holes on every nest and keeps the spacing to the hole's edge. The DXF lists each sheet's contours in cut order — part by part, its marks, its holes, then its outline — with a part in a hole before the part around it. There is no switch yet to keep a slug whole: if the customer wants it, drag the small part out of the hole after the nest.