Laser Kerf Compensation, Finger-Joint Press-Fit Interference & Lens Focal Spot Calculator
Laser Kerf Compensation, Finger-Joint Press-Fit & Lens Focal Spot Calculator
How This Laser Kerf & Press-Fit Solver Calculator Works
Every laser cutter vaporizes a narrow channel of material along the toolpath called the kerf width (K, typically 0.08mm to 0.25mm). If finger joints or mortise-and-tenon slots are drawn at nominal board thickness (T) without kerf compensation, every cut slot widens by +K while every male tab shrinks by -K, resulting in loose, rattling joints. Our interactive Laser Kerf & Press-Fit Solver calculates your exact machine kerf from caliper measurements, outputs compensated CAD slot and tab widths for Slip, Snug, or Mallet press-fit classes, and computes lens focal spot diameter and depth of focus.
Governing Mathematical Equations (ISO 11146 Laser Beam Optics & CNC Press-Fit Interference Joinery Standard)
Determines full beam kerf width from a test cut and the single-side outward toolpath offset required in LightBurn or CAD.
Adjusts CAD vector geometry so the physical post-cut slot and tab interlock with the desired interference pressure (Delta_fit).
Shows why shorter focal length lenses (1.5" / 38.1mm) produce a tighter kerf but shallower depth of focus than 2.5" (63.5mm) lenses.
Standard CO2 Laser Lens Focal Lengths, Spot Sizes & Ideal Material Thicknesses
| Lens Focal Length | Metric Focal (f) | Typical Spot Ø | Depth of Focus (DOF) | Best Material Range |
|---|---|---|---|---|
| 1.5 Inch Lens | 38.1 mm | 0.10 mm | ± 1.1 mm | High-DPI engraving, thin < 3mm wood/Mylar |
| 2.0 Inch Lens (Standard) | 50.8 mm | 0.14 mm | ± 2.0 mm | All-purpose 3.0mm – 6.0mm plywood & acrylic |
| 2.5 Inch Lens | 63.5 mm | 0.18 mm | ± 3.1 mm | 6.0mm – 10.0mm thick wood & deep vertical cuts |
| 4.0 Inch Lens | 101.6 mm | 0.28 mm | ± 8.0 mm | 12mm – 20mm thick foam, MDF & tall recess cuts |
Apply These Calculations in 1:1 Parametric CAD Studios
Laser Cut Finger-Joint Box Generator (with Kerf & Thickness Compensation)
Laser Kerf & Slot Thickness Calibration Test Strip Generator
Flat-Pack CNC Desk Monitor Stand Riser & Keyboard Shelf Generator (DXF/SVG)
Frequently Asked Questions — Laser Kerf & Press-Fit Solver
Why do acrylic and plywood require different interference fit settings?
Wood fibers (Baltic birch, basswood, MDF) compress elastically by 0.02mm–0.05mm during assembly, allowing a tight mallet press-fit without glue. Cast acrylic is brittle and non-compressible—forcing an oversized tenon into an acrylic mortise will crack the corner.
Should I apply kerf compensation in my CAD drawing or in LightBurn?
Never apply both! If you enter your Kerf (K) inside a CadFold parametric generator, the exported .DXF/.SVG already has kerf compensation baked into the vectors—so leave LightBurn's Kerf Offset at 0.00 mm.
Why should I measure sheet thickness with digital calipers before cutting?
Nominal '3mm' plywood or cast acrylic routinely varies between 2.75mm and 3.25mm across batches. Entering your true caliper measurement for T is essential for flush finger joints.