If your finger joints are loose or your inlays rattle, you almost certainly haven't measured your kerf.
How to measure it in five minutes:
- Draw a 100mm × 20mm rectangle. Inside it draw ten vertical lines 10mm apart, all set to cut.
- Cut it in the material you actually use.
- Push all eleven resulting strips tight together and measure the total width with calipers.
- The difference from 100mm, divided by 10 (the number of cuts), is your kerf.
On my LX2 in 3mm birch it's 0.15mm. In 3mm cast acrylic it's 0.19mm. In 6mm ply it's 0.22mm because the beam is diverging over that depth.
Then use it: for a slot that must accept a 3.0mm tab, draw the slot 3.0mm minus one kerf if the cutter runs on-line, or offset your geometry by half a kerf per side. Test on a single joint before committing to a full box.
Kerf also changes with power, speed and focus, so re-measure if you change any of those significantly. Write it on the test tile.
