The question of laser kerf comes up occasionally in Adafruit’s weekly Ask-an-Engineer chat, so I figured this would be of interest to some folks. James Williamson shares his method for finding the kerf of a laser cutter in different materials and material thicknesses. He writes:
Kerf is determined by material properties and thickness, the focal length of the lens and the gas used while cutting. Our laser cutter uses a lens with a 50mm focal length and uses compressed air to push out the vapourised/molten swarf.
By cutting a rectangle of material and then cutting 9 rectangles within it you get 10 cuts. When these 9 rectangles are pushed together at one end of the “frame”, the resulting gap at the other end is the sum of the kerfs. Dividing this gap by ten gives the average kerf for that material and material thickness.
He uses a feeler gauge to measure the width of the gap and then divides by the number of cuts (10, in this case) to get the kerf for that particular material/thickness/feedrate/power combination on his cutter.
Josh Judkins of Ponoko added this in the comments:
We’ve found that kerf widths can vary even on the same material sheet, depending on whether you’re cutting a straight or curved line, or the laser head is moving on the x or y axis.
Good info to keep in mind.
You can check out James’ blog post about it here. Nice work, James!