When you start making finger-jointed boxes, the first thing you look for is a number: "what is my machine's kerf?". The internet is full of tables with values per model and material that promise to save you the test. I am not going to publish one of those, and here is why.
Kerf is not defined by the laser model. It is defined by the whole combination you cut with:
Two people with the same machine can measure different kerfs on the same MDF, and the same person can measure a different kerf a month later because the lens got dirty. A table that says "this model, this material, this kerf" mixes data from setups you know nothing about, so I prefer not to invent a precision that nobody can guarantee.
As a general guide, community guides report values of a few tenths of a millimetre (roughly 0.1 to 0.3 mm) for wood cuts on CO2 lasers, and on diode lasers the result depends a lot on focus and the number of passes. Use that only to sanity-check your measurement: if you get 2 mm or 0.001 mm, something went wrong in the measuring, not in the machine.
This is what I measure, with my machine and my way of cutting, using the 100 mm square method explained below:
| Item | Value |
|---|---|
| Machine | Creality Falcon 10W Pro (diode laser) |
| Software | LightBurn |
| Material | 3 mm MDF |
| Speed | 500 mm/min |
| Power | 80% |
| Passes | 3 |
| Measured kerf | 0.05 mm |
That is well below the 0.1 to 0.3 mm above. One possible explanation is that a fine-spot diode cutting in several slow passes removes little material from each side, but I cannot claim that: all I know is that this is what my calipers show. If I had copied a generic table value, my finger joints would have come out loose. These are the numbers for my setup: use them as an example of the process, not as a value for yours.
For other materials (a thicker MDF, say, or plywood) it is worth measuring the kerf separately, because thickness, number of passes and the ash that builds up in the cut all change.
The method is simple, but three details change the result:
Example with made-up numbers just to illustrate: if the three squares average 99.90 mm, the kerf is (100 − 99.90) ÷ 2 = 0.05 mm.
Then enter that value in the Kerf field of Box Studio and generate a small test box (for example 60 × 40 × 30 mm) before cutting the big one.
This template is the only thing worth keeping. Write one row for each combination you use:
| Material and thickness | Speed | Power | Passes | Lens / focus | Measured kerf | Date |
|---|---|---|---|---|---|---|
| example: 3 mm MDF |
In a few weeks you have a reliable table with your numbers. If you change lens, material batch or settings, repeat the test and add another row.
If one day your joints start coming out different without you changing anything, the first thing to check is the lens.
If the result is a little loose or tight, you don't need to measure everything again: adjust the kerf in steps of 0.02 to 0.05 mm and generate another test box.
Once you have your value, Box Studio compensates all the finger joints automatically. You can also use the kerf calculator to get the number from your measurements.
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