Laser 101 · File & design
Laser kerf and tolerances.
When parts have to fit together, kerf is the number that matters. Here is what it is and how to design around it.
What kerf is
Kerf is the width of material the laser actually removes as it cuts. The beam is focused to a fine point, but it still vaporizes a narrow channel — typically around 0.003″ to 0.005″ wide, depending on the material, its thickness, and the machine settings.
It is small, but it is not zero — and on parts that need to fit together, that small amount is the difference between a snug joint and a sloppy one.
Why kerf matters
Because the beam removes material along the cut line, a finished part comes out very slightly smaller than the outline you drew, and any hole comes out very slightly larger. For a decorative shape that difference is invisible. For a press-fit slot, a gear, or a part that has to mate with something else, it matters.
The good news is that kerf is consistent and predictable, so it can be designed for rather than fought.
Designing parts that fit
For slot-together assemblies — tab-and-slot boxes, finger joints, panels that press into each other — the slot should be drawn a hair narrower than the material is thick, so that once kerf is removed the joint closes to a friction fit.
Two things drive this: the kerf itself and the true thickness of your material, which is often slightly under its nominal size (quarter-inch plywood is rarely exactly 0.25″). Tell us the exact material you are using, and for any precision assembly we recommend cutting one test joint before the full run.
Tolerances you can expect
A CO₂ laser is highly repeatable — cut the same file a hundred times and the parts match. Realistic tolerances are around ±0.005″ for most jobs, influenced by the material more than the machine: heat can slightly affect edges, and thin or warped stock can shift during a cut.
That is excellent for enclosures, models, signage, and most prototyping. For sub-thousandth machining tolerances, a CO₂ laser is not the right tool — that is CNC milling territory. For everything in between, designing with kerf in mind gets you parts that fit the first time.
Common questions
What is kerf in laser cutting?
Kerf is the width of material the laser beam removes as it cuts — typically about 0.003″ to 0.005″, depending on the material and thickness.
How much material does the laser remove?
Roughly 0.003″ to 0.005″ along each cut line. Parts come out slightly smaller than drawn and holes slightly larger by that amount.
How tight a tolerance can you hold?
Around ±0.005″ for most work, and very repeatable run to run. Material movement and heat affect it more than the machine. For sub-thousandth tolerances, CNC milling is the right tool.
How do I design parts that press-fit together?
Draw slots slightly narrower than the material thickness so kerf brings them to a friction fit, and account for the material's true thickness. We recommend a test joint before a full run.
Does kerf change between materials?
Yes, slightly — it varies with the material, its thickness, and the cut settings. Tell us exactly what you are cutting and we account for it.
Need parts that fit?
Industrial CO₂ lasers, beds up to 46 by 58 inches, in downtown Los Angeles. A real person checks every job.