Accounting for Kerf

If you've worked with a laser cutter in the past, or pretty much any woodworking tools, then you'll most likely have heard the advice "don't forget to account for the kerf!" But what is kerf?

 

Accounting For Kerf: How Much Material Is Really Removed By Your Cutter? by Matt Stultz at Make: Magazine

Simply put, kerf is the amount of material that your cutting tool removes from your workpiece. If you don't properly account for the kerf of your beam, blade, or bit then this can leave your work shorter than expected, or too loose to fit together. With laser cutters, there are 2 things to consider when allowing for kerf:

  1. Beam width - This is set by the focal length of your lens, and can vary from machine to machine. 
  2. Material - Wood gets burnt away by the laser leaving the cut edges, but plastics can also melt at the edges leaving a wider gap. Different material thicknesses can also affect the kerf width.

 

Accounting For Kerf: How Much Material Is Really Removed By Your Cutter? by Matt Stultz at Make: Magazine

 So, what's the best way to measure your kerf? Take a spare piece of your material and cut yourself a jig. Matt Stultz over at Make: Magazine has put together a simple jig to help you calculate and account for the kerf. Simply laser cut a key with a given dimension (in this case 20mm) and a series of slots to fit it into that are each .1mm smaller than the last, then press the key into each slot until you find the one that fits it best. The actual kerf is half of the difference of the key and the slot, since the kerf is removed from both sides (e.g., 20mm - 19.6mm = 0.4mm, halve that to 0.2mm for your kerf). You can then use this to adjust your design to get a nice tight tolerance. You can download the jig on the Make: Magazine article to try it for yourself.

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