What is kerf? (And why it matters in laser file designing)
What Is Kerf (and Why It Matters in Laser File Design)
If you’ve ever cut a design that almost fit together (but didn’t) you’ve probably met kerf… even if you didn’t know its name yet.
Kerf is one of the most important (and most overlooked) parts of laser file design. Understanding it can be the difference between a loose, wobbly project and a perfectly snug fit.
Let’s break it down.
What Is Kerf?
Kerf is the width of material removed by the laser as it cuts. When your laser cuts a line, it doesn’t cut infinitely thin. It burns away a tiny amount of material—creating a gap.
That gap is kerf.
Even though it’s small, kerf will affect how your pieces fit together, the overall size of your projects and whether tabs are too loose or tight.
Why Kerf Matters in Laser Cutting
Kerf becomes especially important when you’re designing interlocking pieces, slot-and-tab projects, layered designs, press-fit assemblies, etc.
If you ignore kerf your tabs may fall out, your slots may not accept their matching pieces, your layers may shrink overall size and your 'perfect' design may not assemble as planned.
How Much Kerf Does a Laser Have?
Kerf is not universal. It depends on a few things. Your laser type (diode, CO₂, fiber), lens and focus, power and speed settings, material type and thickness, etc.
As a general starting point, its safe to assume:
- Wood: ~0.15–0.25 mm
- Acrylic: ~0.1–0.2 mm
These are estimates, not rules. That’s why testing your equipment matters. Please use the tool to test your kerf.
How to Measure Kerf (The Easy Way)
One of the simplest methods is a test slot:
- Design a rectangle with a matching slot
- Cut both pieces from your chosen material
- Test the fit
- Adjust the slot width slightly
- Repeat until you get a snug fit
Once you find what works, write it down for that material and thickness. Kerf values change between thicknesses, types and brands.
Option 2:
You can also cut a 1" square.
After cutting, measure both the square and the hole it came from using a caliper. The difference will show you the kerf for that material.
How to Design With Kerf in Mind
There are two common approaches:
1. Adjust Your Slot Sizes
Make slots slightly wider or narrower to compensate for kerf.
Example:
If your material is 6 mm thick and your kerf is 0.2 mm, you may design a slot closer to 5.8 mm for a snug fit.
2. Offset Your Paths
Most design software allows you to offset paths inward or outward to account for kerf across an entire design. This is especially useful for repeated parts, assembly and files you plan to sell.
Common Kerf Mistakes to Avoid
- ❌ Designing “exact” measurements with no testing
- ❌ Assuming kerf is the same for all materials
- ❌ Copying kerf values from someone else’s laser
- ❌ Ignoring kerf in press-fit designs
Kerf is small, but its impact is not.
Final Thoughts: Kerf = Less Waste
Taking the time to understand kerf will save you material in the long run. You'll reduce failed projects, improve your assembly quality and create designs that feel professional.
If you’re designing laser files, especially for others to use, kerf awareness is non-negotiable.
Coming up next in the 'Design like a Pro w. Jellybean's Market' Series:
- Open Paths vs closed paths (how one missing node can ruin a cut)
- Layer order (why engraving before cutting matters)
- What buyers expect in a laser SVG (clean layers, naming and organization)