Kerf Compensation in Laser Cutting
Laser beam width removes material (kerf), making parts slightly smaller than designed. Compensating for kerf ensures precise dimensions and perfect fits.
Understanding Kerf
Kerf is material removed by laser beam—the width of the cut itself. Typical CO2 laser kerf: 0.15-0.3mm depending on material, power, focus. When cutting 100mm square, final piece measures 99.7-99.85mm because kerf removed material on all sides. Difference matters for precision parts.
Kerf varies by material: hardwood wider kerf than softwood (density), thick material wider than thin (beam diverges through thickness), acrylic narrower kerf than wood (cleaner cut). Document kerf for each material/thickness combination. Can't assume same settings produce same kerf across materials.
Inside vs outside cuts affected differently: cutting inside hole makes hole larger by kerf width (material removed from inside). Cutting outside profile makes part smaller by kerf width (material removed from outside). Single design with both features needs different compensation strategies.
Half-kerf principle: cut line follows beam center. Material removed equally on both sides of line. To maintain dimension, offset cut path outward by half kerf width for external profiles, inward by half kerf for internal holes. This preserves design dimensions in final part.
Measuring Your Laser's Kerf
Test cut method: Cut square with known dimension (100mm × 100mm). Measure finished piece with digital calipers. Difference is total kerf loss. Divide by 4 (four sides) = kerf per edge. Example: designed 100mm, measured 99.8mm. Lost 0.2mm total, 0.05mm per edge. Half-kerf = 0.025mm offset needed.
Direct measurement: Cut straight line, measure gap width with calipers or optical measuring scope. Gives kerf directly but requires precision measurement tools (gap only 0.15-0.3mm wide). Test cut method more practical for most shops.
Multiple material tests: Create test matrix—cut identical shapes from each material/thickness combination you use. Label and store samples. Measure, document kerf for each. Build reference library eliminating guesswork. Update when changing laser settings, replacing lenses/mirrors, or switching material suppliers.
Focus height affects kerf: out-of-focus beam wider. Ensure consistent focus for predictable kerf. Change in focus changes kerf—parts won't fit. Maintain focus calibration and document focus distance used for kerf tests.
Applying Kerf Compensation
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Strategy 1: Manual Path Offset
In CAD/design software, offset cut paths by half-kerf amount. External profiles: offset outward (expand). Internal holes: offset inward (shrink). Most vector software has 'offset' or 'outset/inset' function. Apply before export to laser software. Time-consuming for complex designs but maximum control.
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Strategy 2: Laser Software Compensation
Many laser control programs have built-in kerf compensation. Enter half-kerf value, software automatically offsets all cut paths. Advantage: adjust compensation without re-processing design file. Disadvantage: applies same offset to all paths—may need different compensation for different features.
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Strategy 3: Design Dimension Adjustment
For simple parts, adjust design dimensions by full kerf. Example: need 100mm finished part, draw 100.2mm (adding kerf loss). Works for basic shapes but complex parts with both internal and external features need proper offsetting—this method doesn't distinguish direction.
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Test Fit Iteration
Cut test joints—simple tab/slot or male/female interlocking pieces. Measure fit tightness. Too loose: reduce compensation. Too tight: increase compensation. Ideal: press-fit requiring light hand pressure. Adjust in 0.025mm increments. Document final working offset for future projects.
Applications Requiring Compensation
Interlocking assemblies: puzzles, furniture joints, architectural models, enclosures with tabs. Without compensation, female slots too tight (designed for male part dimension but material removed from male part by kerf). With compensation, male parts slightly oversized, female slots slightly undersized—parts fit perfectly.
Mounting holes: PCB mounting, brackets, template guides. Hole diameter critical for bolt/pin fit. Without compensation, holes too large (kerf expands hole). Inward offset shrinks hole to correct diameter. Especially important for press-fit bearings, bushings, or precision alignment features.
Layered stack designs: multiple identical parts stacking to create 3D object. Kerf mismatch causes layers not to align—stack leans or wobbles. Consistent kerf compensation ensures all layers identical size, stack aligns perfectly. Critical for architectural models, terrain maps, decorative boxes.
Not always needed: decorative items without fit requirements don't need compensation. Signs, art pieces, standalone objects rarely need precision beyond ±0.5mm. Save time by skipping compensation for non-critical work. Focus compensation effort on functional parts requiring precise fit.
Do I compensate inward or outward?
Depends on feature type. External profiles (part outline, male connectors): offset outward—makes design larger to account for material removed from outside. Internal features (holes, slots, female connectors): offset inward—makes design smaller to account for material removed from inside expanding the feature. Remember: laser follows path center, removes material both sides. Offset always in direction that preserves your intended dimension in finished part.
My parts fit perfectly on one material but not another. Why?
Kerf differs by material. Dense hardwood wider kerf than softwood. Acrylic narrower kerf than wood. Each material/thickness needs separate kerf measurement and compensation value. Can't use same offset across materials. Solution: test kerf for each material, document values, apply material-specific compensation. Some laser software allows saving material profiles with kerf values—select material, compensation auto-applies.
Is kerf compensation the same as laser beam width?
Not exactly. Laser beam width at focus typically 0.1-0.2mm, but kerf (cut width) often wider: 0.15-0.3mm. Additional width from: material burning beyond beam spot (charring zone), material melting/vaporizing slightly beyond direct beam exposure, beam divergence through material thickness. Kerf must be measured empirically—can't calculate from beam specs alone. Always measure actual cut width for accurate compensation.
Verification checklist before production
- Confirm final size, units, and orientation in the destination software
- Inspect the file for hidden, duplicate, or irrelevant geometry
- Run a small material or sew-out test before full production
- Save the approved settings, source file, and exported production file together
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