Enrichment · Arts & Creativity · Making

Draw it a little off
so it cuts out exact.

Cut a row of test squares and measure them. The calculator finds the width the laser burns away, then tells you what size to draw each edge, hole, tab and slot so parts come out the size you meant and joints fit.

Find the kerfWhat you get

The kerf compensation calculator

The worked example is a made-up test cut in 3 mm birch plywood for a finger-jointed box. Nothing you type leaves this browser.

Loading the calculator. If nothing appears, turn on JavaScript.

What you get

Enrichment · Arts & CreativityFree

What you finish with
The kerf, the offset per edge and the size to draw each feature for an exact, press or sliding fit. It prints as a cut sheet and downloads as a spreadsheet.
Who it is for
Makerspace and engineering students, technology and design teachers, and hobbyists with a laser cutter.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Arts & Creativity space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Draw a row of squares sharing edges and cut it with your usual settings.
  2. Push the pieces together and measure the row with calipers.
  3. Type the drawn size, count and measured length.
  4. List each feature with its finished size and fit.
  5. Draw the sizes shown, or offset paths by half the kerf.

Find the kerf

How the compensation works

Measure what the beam removes, then add it back.

The worked example: 3 mm birch plywoodDrawn100.00 mm5 squares × 20 mmMeasured99.10 mmafter cuttingKerf0.18 mm0.90 ÷ 5 cutsBox sidedraw 100.18for 100 mm finishedThe worked example: 3 mm birch plywoodDrawn100.00 mm5 squares × 20 mmMeasured99.10 mmafter cuttingKerf0.18 mm0.90 ÷ 5 cutsBox sidedraw 100.18for 100 mm finished
The beam burns away a strip the width of the kerf, half from each side of every line you draw.

What kerf is

A laser does not cut a line of zero width; it vaporizes a narrow strip, often 0.1 to 0.3 mm in wood and acrylic. Half of that strip comes off each side of the line you drew. A part comes out smaller than drawn and a hole comes out bigger, which is why press-fit joints drawn to exact size end up loose.

Why a row of squares

One square loses only a fraction of a millimetre, hard to read even with calipers. A row of five cut from shared lines loses five kerfs in total, so the measurement is five times easier to read and errors are divided by five. Repeat the test whenever material, power, speed or focus change.

Sources

  1. National Institute of Standards and Technology. Dimensional metrology: using calipers and repeated measurements (nist.gov).
  2. American Society of Mechanical Engineers. ASME Y14.5, Dimensioning and Tolerancing: fits and allowances (asme.org).
  3. U.S. Occupational Safety and Health Administration. Laser hazards and safe operation (osha.gov).
  4. U.S. Food and Drug Administration. Laser products and instruments: safety classes (fda.gov).

The worked example is made up. Never leave a laser cutter running unattended. Your entries stay in this browser. Support: team@caveatacademic.com.