Kerf width for fiber laser and plasma: chart by thickness and amperage

Plasma kerf by thickness and amperage

From Hypertherm's Powermax45 XP/65/85/105 cut chart guide: mild steel, air, standard cartridges, Best Quality settings. Hypertherm says the kerf values are for reference only and that installations and material vary. Two things stand out: more amperage cuts wider at the same thickness (2.3 mm instead of 1.5 mm at 6 mm), and the FineCut cartridges for thin sheet cut much narrower, 0.5–0.9 mm on 0.5–4 mm mild steel at 40–45 A.

Fiber laser kerf: what is published

• No fiber laser maker's kerf chart was available to us, and LaserCalc Pro's kerf guide says it assumes no public kerf benchmark either.
• MachineMFG gives 0.3–0.5 mm for laser cuts in material under 3 mm and 0.2–1 mm for 10 mm plate — generic ranges with no source, power or gas named.
• A 2018 study (Musil et al.) gives 0.2–0.5 mm on 4 mm AISI 304 stainless — on a 3 kW CO2 laser with nitrogen, not a fiber laser.
• SendCutSend says two parts nested on one shared cut line end up 0.006–0.012 in (0.15–0.30 mm) apart, depending on material: in effect one kerf, on its laser and waterjet machines.
• Kerf grows with thickness and changes with speed, focus, nozzle and gas: MachineMFG notes it narrows as the speed rises, is narrowest with the focus on the surface, and grows as a machine wears.

Kerf compensation: where it is set

• CypCut: select the parts and click Compensation (V6.5 manual §3.2, “Seam Compensation”). The value should come from measuring a real cut; the compensated path is drawn in white and becomes the tool path. The CypCutPro manual states the rule: inner contours shrink, outer contours grow. A round-corner option smooths the offset at corners.
• CypNest: the Kerf Compensation dialog takes an outer and inner width from a test cut — half the measured kerf, per the manual — and compensation must be added before co-edge cutting.
• SheetCAM: the kerf width is part of the plasma, laser or waterjet tool. The contour operation's Inside offset or Outside offset moves the path by half of it; No offset cuts on the line.
• Zorocut: none. It exports the parts at drawing size (LINE, ARC and CIRCLE in mm) and the controller or CAM adds the offset. Do not also shrink or grow the drawing yourself, or the part comes out a kerf too small or too big.

Kerf and part spacing

With compensation on, each part's cut removes a full kerf outside its edge, so the metal left between two parts is the spacing minus two kerf widths (simple geometry). On a fiber laser that costs a few tenths of a millimetre. On plasma it decides the gap: 3 mm parts at 45 A with a 3 mm gap would keep only 3 − 2 × 1.4 = 0.2 mm of web, so give plasma jobs a wider spacing than laser jobs. Start from the values in part spacing; common-line cutting is the one case where two parts share a kerf on purpose.