What Is Kerf Compensation?

If you've ever laser-cut a box and found the finger joints are loose, kerf is probably why. Understanding kerf and how to compensate for it is the difference between a wobbly box and one that holds together with a satisfying snap.

What is kerf?

Kerf is the width of material removed by the laser beam as it cuts. A laser doesn't cut an infinitely thin line. It vaporizes a small strip of material, typically between 0.1mm and 0.3mm wide, depending on the laser, material, and settings.

This means every cut piece comes out slightly smaller than the design. A panel designed to be 100mm wide might actually measure 99.8mm after cutting, because the laser ate 0.1mm from each edge.

Why kerf matters for finger joints

Finger joints work by alternating tabs and slots along an edge. Tab A fits into Slot B. If both the tab and the slot lose material to kerf, you get a double penalty: the tab is narrower than designed, and the slot is wider. The result is a loose, sloppy fit.

Without kerf compensation, a 3mm tab cut from 3mm plywood might actually be 2.7mm wide, fitting into a slot that's 3.3mm wide. That's 0.6mm of play, which is enough to make the joint feel flimsy.

How kerf compensation works

Kerf compensation adjusts the geometry at export time to account for the material the laser will remove. Tabs are made slightly wider, and slots slightly narrower, so the final cut pieces match the intended dimensions.

The key insight: kerf compensation is an export-time operation, not a design-time one. Your geometry is defined in nominal (ideal) dimensions. The compensation is applied when the SVG is generated for cutting. This keeps the design clean and makes it easy to adjust for different lasers or materials.

How Craft Ready Cuts handles kerf

Craft Ready Cuts applies kerf compensation automatically based on your selected material and machine. You can also override the kerf width manually if you know your specific laser's kerf from testing.

The workflow is:

1. Design your box with nominal dimensions
2. Select your material (each material has a default kerf value)
3. Optionally adjust kerf in the settings panel
4. Craft Ready Cuts applies compensation when you download the SVG
5. The downloaded file is ready to cut with no further adjustment

How to measure your laser's kerf

If you want precise results, measure your specific laser's kerf:

1. Cut a straight line in a scrap piece of your material
2. Push the two halves back together
3. Measure the gap with calipers
4. That gap is your kerf width

Most diode lasers (like xTool D1) have a kerf around 0.15-0.25mm in wood. CO2 lasers (like Glowforge) are typically 0.1-0.2mm. Acrylic tends to have a narrower kerf than wood.

Fit profiles

Beyond raw kerf compensation, Craft Ready Cuts offers fit profiles that add a small additional offset:

• Standard fit: Designed for a snug press fit that holds without glue
• Tight fit: For joints that need to stay permanently assembled
• Loose fit: For joints that need to slide or be disassembled

The fit profile works on top of kerf compensation. It's the fine-tuning layer that accounts for the difference between "mathematically correct" and "physically satisfying."