Common-line cutting: when sharing an edge pays, and why Zorocut leaves it to the controller

What it saves

Every separate contour costs a pierce and a lead-in, and two parts side by side cut two parallel lines a few millimetres apart. Sharing the line removes one of them and, in a chained array, many of the pierces. How much depends entirely on the job: figures such as “85 % fewer pierces” circulate on vendor blogs without a job you can check, so work it out on your own parts — the quote's cut length and pierce count show the difference.

How nesting programs do it

• CypNest (Bochu): co-edge in auto-nest, as an array or by hand, with a minimum co-edge length, a mode limited to a maximum number of parts, an “only same parts” rule and a part-gap check for the parts that are not shared. Kerf compensation has to be applied before the co-edge.
• ProNest (Hypertherm): an optional Common Line Cutting module that shares edges automatically for similar parts and by hand for different profiles, with kerf compensation.
• Kinetic PrimeCut: the parts must be lined up in a row, column or array; the shared cut is written without kerf compensation, so the kerf can no longer be adjusted at the machine. Its help warns about cut quality on plasma, where one side of the cut is the good side.

Why Zorocut does not write shared edges

CypCut, CypCutPro and CypCutE delete duplicate lines when they import a DXF. If two parts shared one line in the file, the import would remove one copy and could leave a contour open — drawn in red and not cut as a part. So Zorocut always keeps the part spacing above zero and lets the controller build the common line with its own co-edge function, where the kerf and the lead-ins are known.

When not to use it

• Plasma: the kerf is 1.3–2.1 mm wide on a 45 A torch and one side of the cut is the scrap side; a shared cut puts one of the two parts on it.
• Small parts: a part cut free on all sides at once can tip on the slats.
• Different parts: the gain is on long identical straight edges, which is why CypNest offers an “only same parts” rule.
• Tight tolerances: the shared line takes its kerf from both parts at once, so the compensation must be decided before the nest — and a DXF without toolpaths cannot carry it.