What it is
In an ordinary nest every part keeps a gap to its neighbours, and every part has its own complete outline to cut. With common-line cutting, two parts are placed edge to edge so that the line between them is cut once. The beam or arc runs down the middle of the shared edge, and each part takes one side of the kerf.
That one change saves on three things at once:
- Cut length. The shared edge is cut once instead of twice.
- Pierces and travel. A cluster of parts can be cut as one shape, with fewer starts and fewer rapid moves between them.
- Material. The gap between the two parts disappears, so the cluster takes less sheet.
When it pays
- Straight edges. Rectangles, panels, strips, brackets with long flat sides. The more straight edge two parts have in common, the more it saves.
- Quantity. Twenty copies of the same panel in a grid share far more edge than two odd parts that happen to touch.
- Plasma. Pierces wear plasma consumables faster than anything else, so cutting a cluster as one shape is often worth more in nozzles than in material.
- Thin sheet on a laser. A narrow, consistent kerf makes shared edges clean, and thin material is where cut time is mostly travel and pierces.
When it does not
- Curved parts. Two curves rarely match, so there is little edge to share.
- Edges that need different treatment. If one side of the shared edge needs a lead-in, a tab or a different cut quality, sharing it gets in the way.
- Parts that must not move. When the last shared cut frees a cluster, parts can shift or tip. Small, light parts on slats are the usual victims.
- A CAM setup that cannot follow it. The shared path has to be cut on the line, with no compensation. If your CAM cannot do that for one layer, a shared cut will come out at the wrong size.
Panels and plates set to share cuts sit edge to edge in clusters (14 shared cuts on this sheet); every other part keeps its ordinary spacing.
How SheetNest does it
You choose which parts may share
Each part has a Common cutting setting in Edit Part:
- None: the part never shares a cut and keeps its full spacing to everything.
- Unrestricted (compatible parts): the part may share a cut with any other part that also allows it.
- Same part: the part shares a cut only with copies of itself. Useful when mixing parts in one cluster would make sorting harder.
The nest comes first, then the shared edges
SheetNest first lays the whole job out with ordinary spacing. Then it looks for straight edges that compatible parts could share, pulls those parts together into clusters, and keeps a cluster only if it does not use more sheet than the ordinary layout did. Every part that is not in a cluster keeps its normal spacing, and so does every edge of a clustered part that is not shared.
The two shared edges sit at the Common Line Gap, a small separation set in Advanced Settings (0.010 in, or 0.254 mm, by default), and the cut runs down the middle of it.
The DXF your CAM reads
Each sheet exports as one DXF with the cuts on three layers, in the order they should run:
01_CUT_INNER: holes and other inside contours.02_COMMON_LINE: the shared cuts, to be cut on the line with no offset.03_CUT_OUTER: the closed outside boundary of each cluster, and the outsides of ordinary parts.
There is no second copy of a line under the shared cut, so your CAM does not have to find and delete duplicates. SheetNest adds no lead-in or lead-out on the shared path: those stay in your CAM software, where they belong.
Limits worth knowing
- Shared cuts are found on straight outside edges. Holes never share a cut, with each other or with an outside.
- The search is bounded. It can miss a valid arrangement, and when a shared cut cannot be resolved cleanly it is dropped rather than guessed.
- Before running a production job, import one exported sheet into your CAM and make a trial cut.