Curiosity.diy · Laser bench

Kerf Test Comb Maker

One strip, a row of slots, each a hair different. Find the slot your board actually grips in — that tells you your kerf. Two minutes of cutting saves a whole sheet.

What the comb is for. A laser beam has width. Cut a 3.0 mm slot and you get back something wider than 3.0 mm, so a 3.0 mm tab flops around in it. The comb cuts a ladder of slots stepping down from nominal thickness. The slot your board slides into by hand but grips firmly is the fit. kerf = nominal thickness − that slot width. Feed that number into Box Maker or the Astounding Shape Designer and every joint closes tight. Kerf changes with machine, power, speed, lens and the board — so cut a fresh comb whenever any of those change.

Comb

Sheet

Document—
Combs1
Slot range—
Kerf range tested—

Download

Both files share one origin and one page size. Import the JPG, engrave the numbers, then import the SVG over the top at 0,0 and cut. The 4 mm square at the top-left corner appears in both — line the squares up and everything else lands.

Cut lines — SVG Engraved numbers — JPG Registration square at 0,0 — both files

How to use it

Cut the comb

  1. Engrave the JPG first, on the very board you plan to build from, at your usual settings.
  2. Cut the SVG over it without moving the board.
  3. Take a scrap of the same board and try its edge in each slot, working from the widest down.

Read the comb

  • Too loose: it rattles. Too tight: it needs a mallet, or splits the land.
  • The right one goes in with firm thumb pressure and stays put when you tip the comb over.
  • Read the engraved number on that slot. kerf = nominal − slot. If 3 mm ply grips the 2.85 slot, your kerf is 0.15 mm.

Why nominal lies

Ply is rarely the thickness on the label — "3 mm" birch often measures 2.9. That's fine. Measure your board with calipers, set that as nominal here, and the comb tells you the true kerf for that board rather than for a number on a packing slip. Write the answer on the board with a marker and on the wall above the machine.