Kerf and offcut: what a linear cutting plan has to account for

Updated: 2026-08-13 · ISKRIT

A linear cutting plan that ignores the blade is short by one part on every long bar. Kerf, end trim and the remnant threshold are the three settings that separate an arithmetic exercise from a plan the saw can run.

Kerf

Kerf is the width of material the cut destroys. It is a property of the machine, not of the bar: an abrasive chop saw takes 2.5 to 3.5 mm, a band saw 1.3 to 2.0 mm, a cold saw around 2.5 mm, a plasma torch 3 to 5 mm, and a hydraulic rebar shear takes nothing at all because it displaces steel instead of removing it.

The arithmetic is unforgiving. Cutting 12 pieces of 990 mm from a 12 000 mm bar looks like a perfect fit: 12 × 990 = 11 880 mm, 120 mm to spare. Add a 3 mm kerf and the eleven internal cuts consume 33 mm, which still fits. Ask for 12 pieces of 1000 mm and the same bar yields eleven, not twelve, because 11 × 1000 + 11 × 3 = 11 033 mm leaves 967 mm, short of a full part. One millimetre of assumed kerf, multiplied across a schedule, is the difference between ordering 100 bars and ordering 102.

End trim

Mill lengths arrive with damaged, out-of-square or painted ends. A trim allowance removes a fixed amount from one or both ends before any part is placed. Trim is not kerf: it applies once per stock length rather than once per cut, and it applies even when the plan makes a single cut.

Trim and kerf are often confused in spreadsheets, and the confusion is asymmetric. Treating trim as kerf understates consumption on bars with few cuts; treating kerf as trim understates it on bars with many.

Remnant threshold

What is left at the end of a stock length is either inventory or scrap, and the boundary is a business decision rather than a calculation. Two numbers define it: the shortest remnant worth racking, and the longest piece not worth handling. Below the lower bound the drop goes to the skip. Above the upper bound it returns to stock and reappears as an input on the next job.

Set the threshold at 1000 mm and a plan optimised purely for yield will happily leave twenty 800 mm drops that all become scrap. Set it at 300 mm and the rack fills with pieces nobody will ever pull. The threshold belongs in the plan, not in a note beside it, because the optimiser can trade a slightly worse yield for remnants that clear the bar.

What to check before ordering

The linear cutting optimizer takes all four as explicit inputs and reports reusable remnant separately from scrap, so the yield figure means the same thing to the buyer and to the saw operator.