Lead-in and lead-out for laser and plasma: types, length and placement

Why leads exist: CypNest's manual says a cut that starts directly on the part can damage it, and the right lead length keeps heat and pierce debris off the part's edge. SheetCAM's tutorial puts it plainly — a plasma pierce leaves an ugly mark, so pierce away from the edge and move in. The lead-out does the same at the end: CypNest's “lead out laser off” keeps the part from dropping and stops overburn as the cut closes.

Types and settings

Line or arc, and how long

• Line is the usual laser choice, per CypNest. On thick plate it recommends Arc or Line + Arc, because a straight lead can overheat the start.
• An arc lead ends tangent to the contour (CypCut §3.1.2), so the cut runs in without a dwell mark — SheetCAM's plasma tutorial uses a 5 mm arc.
• On plasma near the maximum pierce thickness, Hypertherm's Powermax65/85 manual says to allow a lead-in about equal to the thickness — 20 mm on 20 mm plate — and not to drop to cut height until the torch has cleared the molten puddle. The pierce height is generally 2.5 times the cut height.
• On thick stainless, CypCut's lead technique (§3.13.4) pierces, lifts to a lead height to blow away the plasma cloud, then cuts a “stable distance” at a slower lead speed before normal cutting.

Where to put them

• On the scrap side: outer contours lead in from outside, holes from inside. CypCut sets this when it sorts inner and outer contours; check any contour it got wrong.
• Away from sharp corners: CypNest's “lead in from part tip” takes a skip distance so the lead does not burn the corner, and “lead in from long edge” puts it on the longest side.
• Away from fits, sealing faces and edges the customer sees: the entry point always leaves a small mark.
• Close the contour on purpose: CypCut's technical column has Overcut, Gap, Seal and Multi-cut. An overcut runs the cut slightly past its start; a gap stops it short and leaves material — Kinetic PrimeCut builds micro-joints exactly this way, as a negative overshoot. On holes, Hypertherm's True Hole process uses semicircle lead-ins, as Kinetic's tutorial shows.

Leads need room: spacing and holes

Zorocut does not add leads — it exports the contours, and CypCut, CypNest or SheetCAM adds them — but its spacing decides whether they fit. An outside lead sits in the gap between two parts, and the pierce is wider than the kerf: SheetCAM has a setting for it (start point tool clearance, 200 % if the pierce is twice the kerf). A 5 mm lead at 45° starts about 3.5 mm out from the edge (geometry), more than a 3 mm gap. So shorten the lead, aim it where the neighbour is far away, or raise the spacing; on plasma, plan the gap as at least the lead length plus the pierce (estimate). Holes need the same room inside — see minimum hole size.