Laser Kerf Test & Press-Fit Gauge

What it is for

Every laser burns away a thin strip of material along each cut: the kerf. It depends on the lens, the power, the speed and the material, and it is usually somewhere between 0.05 and 0.3 mm. That sounds tiny, but finger joints, slots and sliding lids live or die by a tenth of a millimetre. This tool generates two small test parts and turns your measurement into settings.

The kerf frame is a plate with an opening divided into equal pieces. The press-fit comb has slots from slightly narrower to slightly wider than your material, each with its offset engraved next to it. After cutting, you enter the gap you measured and the slot that felt right, and the tool tells you the kerf compensation and the fit clearance to use in the finger-joint box and living hinge generators.

Worked example

The first example is a test for 3 mm plywood: 10 pieces of 10 mm, and a comb with seven slots from −0.30 to +0.30 mm in 0.1 mm steps. The tool says:

Cut the frame and the comb from 3 mm material, push the 10 pieces to one side, measure the gap and divide it by 11.

Why 11? The opening is cut on both sides and between the pieces, so eleven cut lines cross the strip and each takes one kerf.

The second example enters the measurement: a 1.65 mm gap, and slot 3 felt like the fit you want. The result:

Kerf from a 1.65 mm gap over 11 cuts: 0.15 mm.

Slot 3 was cut at 2.9 mm (thickness − 0.10 mm), and the laser widened it by one kerf. With kerf compensation of 0.15 mm, a fit clearance of 0.05 mm gives slots and sliding lids the same feel.

How to read the result

• Kerf frame opening is the nominal length of the strip of pieces.
• Comb slots shows the range of offsets; the table lists every slot with its nominal width.
• Measured kerf appears once you enter a gap: gap ÷ (pieces + 1).
• Suggested fit clearance appears when you also enter a slot number.
• In the cut file, black is engraving: run it as a light pass or a score before cutting.

Tips and common mistakes

• Cut the test without kerf compensation; it measures the raw kerf.
• Push all pieces firmly to one side and measure the single gap with calipers, not a ruler.
• Use an offcut of the same sheet to try the comb slots; thickness varies between sheets.
• If your laser cuts wider in one direction, cut a second frame turned by 90° and compare.
• Repeat the test when you change the lens, the material or the cutting speed.

FAQ

What is a typical kerf?

For CO₂ lasers in 3 mm plywood it is often 0.1–0.2 mm, but measure your own machine; the tool warns above 1 mm.

Why do I need both the frame and the comb?

The frame gives a number for the kerf. The comb shows which clearance you like, which depends on the material and on taste.

Where do I enter the results?

In Kerfwise, Use this kerf for boxes and hinges copies the kerf, fit and thickness into the box and hinge settings. On the tool pages, enter them as Kerf compensation and Fit clearance.

Does the comb work for acrylic?

Yes. Acrylic barely compresses, so pick the slot that slides in with light pressure rather than a tight one.