Free Laser Cutter Kerf & Speed Calculator
Calculate laser spot diameter, vector kerf compensation offsets, and feed speed estimates for press-fit finger joints and inlays.
⚙️ Laser & Material Parameters
📊 Calculated Kerf & Offsets
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Understanding Laser Kerf & Vector Compensation
The kerf of a laser cutter is the width of material vaporized by the focused beam spot as it travels through the substrate. Unlike a mechanical CNC endmill where cutter diameter is fixed, a laser's kerf depends on the lens focal length, laser wavelength, optical power density, material thermal conductivity, and cutting speed.
How to Offset for Tight Finger Joints
When cutting interlocking finger joints or tabs, the laser beam vaporizes material on both sides of the line. To achieve a tight friction fit without sloppy tolerances, offset external contours outward by exactly half the kerf ($k / 2$) and internal slots inward by ($k / 2$).
Focal Length vs Beam Waist
A 1.5" lens produces a tiny focal spot (~0.08mm) with a shallow depth of focus, perfect for intricate paper and thin acrylic. A 2.5" or 4.0" lens has a larger spot (~0.25mm) but creates straighter vertical cut walls in thick wood (6mm - 12mm).
Frequently Asked Questions
How do I measure my laser's exact kerf experimentally?
Cut a 50mm square divided into 10 equal 5mm strips. Push all 10 cut strips together tightly against a straight edge. Measure the total width with digital calipers. Subtract this total from 50mm and divide the difference by 10 (the number of cut lines) to get your true kerf down to 0.01mm.
What is the difference between kerf and spot size?
Spot size is the theoretical optical diameter of the focused beam at the focal plane. Kerf is the actual physical slot left behind in the material, which is always slightly wider than the spot size due to thermal heat transfer and material melting/flaring.
Where do I enter kerf offset in LightBurn?
In LightBurn, select your cut layer, open the Cut Settings Editor, look for 'Kerf Offset' under the Advanced tab, and enter positive values for outward offsets or negative values for inward offsets.