Kerf width by cutting process

What kerf is

Every cutting process removes a slot of material as it cuts: the laser beam, the plasma arc, the water and abrasive stream, or the router bit. The width of that slot is the kerf. It decides how close parts can sit on a sheet, how small a hole can be, and how far the machine has to offset its path so the part comes out at the size drawn.

Kerf chart by process

Laser makers do not publish kerf-by-thickness charts; the laser rows come from a laser machine builder's guide and a cutting service's published figures. The plasma row spans Hypertherm's Powermax65, 85, 105 and 125 cut charts, from FineCut on thin sheet to 105 A on 1-1/2 in plate. Waterjet kerf is usually close to the mixing tube's bore: OMAX says the kerf normally equals the width of the mixing tube, and Flow gives .030 to .040 in for metals. It grows as the tube wears.

Plasma kerf by thickness

Hypertherm publishes an estimated kerf-width table with the Powermax125 cut charts. These are its figures for mild steel with shielded consumables:

Hypertherm gives these as estimates for reference. Its cut-chart data comes from lab testing with new consumables, and differences between installations and material can change the result.

Kerf compensation: draw parts at finished size

The machine does not cut on the line you drew. It runs offset to the outside of a part's outline and to the inside of its holes by half the kerf, so the finished part matches the drawing. OMAX puts it simply: the offset normally equals half the kerf, for example .015 in for a .030 in kerf.

• The offset is applied either by the CAM software when it writes the path, or by the machine control from a compensation code (G41 and G42), set at the machine.
• So a DXF for cutting is drawn at the part's finished size. Do not shrink or grow it for kerf yourself.
• If the shop's machine already compensates, compensating in the drawing as well cuts the part wrong twice.

Kerf and part spacing in a nest

Parts on a nest need a gap between them wider than the kerf, so both cuts fit and the web between them holds the sheet together. How much more depends on the process: heat makes laser and plasma parts move, a router's bit has to fit between parts, and a waterjet, though it adds no heat, still needs room for the stream and to hold the parts.

• Cutting services publish their own minimums: Xometry's nesting guide uses .03 in between laser parts and .125 in between waterjet parts, with a .25 in margin to the sheet edge.
• On a router the gap has to be at least the bit's diameter, plus a little clearance; Vectric's nesting help gives .25 + .05 = .30 in for a 1/4 in bit.
• When it opens, Nestor will start the part spacing at .125 in for laser, .250 in for plasma, .125 in for waterjet, and the bit plus 1/16 in for a router (.313 in for a 1/4 in bit). It can be changed to suit the machine.