Kerf width is the amount of material removed by the cutting process, essentially the width of the cut slot. Understanding waterjet kerf is critical for efficient nesting—the arrangement of parts on a raw sheet to maximize material utilization.

Typical Kerf Widths

Waterjet kerf varies significantly depending on whether you are using pure water or abrasive, as well as the nozzle size and material thickness.

Pure waterjet (no abrasive): The kerf is extremely narrow, typically ranging from 0.003 to 0.007 inches (0.08 to 0.18 mm). This is because only a tiny orifice (usually 0.004–0.010 inches) produces the cutting stream. Pure waterjet is used for soft materials like foam, rubber, gaskets, and thin plastics.

Abrasive waterjet: The kerf is wider due to the mixing tube (nozzle) diameter, typically ranging from 0.020 to 0.060 inches (0.5 to 1.5 mm). The most common nozzle sizes are 0.030 and 0.040 inches (0.76 and 1.0 mm), producing kerfs of approximately 0.032 and 0.042 inches respectively. Thicker materials and slower cutting speeds can slightly increase kerf due to secondary erosion.

Factors that widen kerf: Lower pressure, slower cutting speed, worn nozzles, larger abrasive grit size, and softer materials all tend to produce a wider kerf. Conversely, high pressure, fast cutting, new nozzles, and fine abrasive minimize kerf width.

How Kerf Affects Nesting

Nesting is the process of arranging cut parts on a raw sheet to minimize scrap. Kerf directly impacts nesting efficiency in several ways.

1. Part Spacing (Micro-tabbing)

When nesting multiple parts, you must leave a gap between them equal to at least the kerf width. If parts are placed too close, the cutting stream will cut into the adjacent part, ruining both. For abrasive waterjet with a 0.040-inch kerf, you typically need 0.045–0.050 inches between parts to ensure a clean separation. Pure waterjet with 0.005-inch kerf can nest parts much tighter, often with only 0.010-inch gaps.

2. Material Utilization Percentage

Larger kerf means more material turns into kerf dust (waste). For a simple example: if you are cutting 10,000 small parts from a large sheet, even an extra 0.020 inches of kerf per part adds up. Over 10,000 linear inches of cut, a 0.040-inch kerf removes 400 square inches of material that could have been parts. For high-volume production, switching from a 0.060-inch to a 0.030-inch nozzle can improve material yield by 3–5 percentage points, saving significant cost.

3. Offset Compensation in CAM Software

Good nesting software automatically applies a kerf offset. The toolpath is shifted to one side of the desired part outline by half the kerf width. If you do not compensate correctly, external dimensions will be undersized by one kerf width, and internal holes will be oversized. Accurate kerf measurement and consistent nozzle wear monitoring are essential for maintaining dimensional accuracy.

4. Thin and Delicate Materials

On thin sheet metal, plastic, or foil, kerf is relatively more significant. A 0.040-inch kerf on 0.020-inch thick stainless steel represents a substantial loss of material. Pure waterjet is preferred for these applications not only for edge quality but also for its ultra-narrow kerf, which allows highly dense nesting.

5. Web Remnants (Skeleton Waste)

After cutting, the remaining sheet (skeleton) contains narrow webs between part locations. Wider kerf produces smaller, weaker webs that may collapse, making part removal difficult. Narrow kerf leaves stronger skeletons that hold parts in position until manual removal.

Practical Recommendations

Measure your actual kerf regularly using a scrap piece, as nozzle wear increases kerf over time.

For high-volume nesting, use the smallest practical nozzle size (e.g., 0.030 inches) to maximize material yield.

When nesting pure waterjet jobs, take full advantage of the ultra-narrow kerf to achieve extremely dense layouts.

Always add a safety margin of 0.005–0.010 inches beyond the measured kerf when setting part-to-part gaps.

Kerf width directly impacts your material cost and nesting density. While abrasive waterjet kerf is larger than laser or pure waterjet, proper nozzle selection and accurate offset compensation can still achieve excellent material utilization. Monitoring kerf and adjusting nesting parameters regularly ensures you are not wasting material unnecessarily.