Kerf compensation
The laser beam has width. Cut parts come out smaller than the design unless you compensate.
When the laser cuts, it vaporizes a strip of material the width of the beam, the kerf. The cut line splits the material into "inside the cut" and "outside the cut", and both sides lose half the kerf width.
If your design has a 50 × 50 mm square and your kerf is 0.2 mm, the resulting part is approximately 49.8 × 49.8 mm. Hole cutouts come out 0.2 mm bigger than the design.
For decorative work this often does not matter. For mating parts (slot-and-tab assemblies, press-fits, gear teeth), it matters a lot.
The basics
Measure your kerf:
- Cut a test square in your material.
- Measure the part's actual dimensions.
- Subtract from the design dimensions.
- The difference is the total kerf loss. Half of that is your kerf radius.
A diode laser kerf is typically 0.1 to 0.3 mm. CO2 is usually 0.15 to 0.3 mm.
Two ways to compensate
1. Per-layer kerf
Set the Kerf field on the layer (visible in the quick-edit strip of the Cuts/Layers panel for line / cut layers). The planner offsets the cut path by the kerf radius before generating G-code. Outline cuts grow by half the kerf; hole cuts shrink.
This is the cleanest way for an entire project. Set it once per material.
2. Manual offset
Use the Offset dialog on specific shapes with Direction: Inward and Distance: kerf/2. The original shape is preserved (or deleted, via the toggle) and you get a new compensated path.
Use this when only some shapes need compensation, or when you want explicit control.
How Beam Bench handles it
Layer-level kerf is the canonical surface. Each layer's Kerf value is applied at planning time, so the Preview shows the compensated path. Save kerf values into your material presets in the Material Library.
When it matters
- Slot-and-tab assemblies: slots need to be the material thickness + tolerance, not the design width minus kerf.
- Press-fit parts: being 0.4 mm too small (two cuts worth of kerf) is the difference between snug fit and falling out.
- Gear teeth: kerf changes the effective tooth profile.
For decorative engraving and isolated shapes, kerf does not matter.
When direction matters
- Outline cuts (cutting around the part): compensate outward so the part comes out at design size.
- Hole cuts (cutting out the inside): compensate inward so the hole comes out at design size.
Beam Bench's per-layer Kerf handles direction automatically based on inside vs outside.