K40 engraving calibration instructions

Today I’m writing about how to calibrate the drop in controller so you get the best engraving from the K40 laser. While I was at the Makerfaire in San Mateo, I realised during the conversion of Nick’s K40 machine that I never wrote instructions on how to get the best engraving. Nick was so friendly to lend me his machine so I did not had to bring one from Australia or buy one online in the US.

In a nutshell it entails three simple steps that you iterate until you get the desired end result.

Step One: Set the engraving range in the Controller.

The engraving range is set in the controller by setting parameter $30. I normally start with a value of 1024.

Step Two: Load a picture into Inkscape and generate an engraving file from the extensions menu. I set a Gray scale of 256 and a resolution of 15 pixel (380 dpi). The engraving speed setting is between 700 and 1000 mm/s for that grayscale and resolution (highest quality and slowest of all settings, others allow you to go faster). Then we load that generated file into the G-code sender (any will do) and run an engraving. Tip: engravings can take a long time so starting with a small picture or area get you faster to the finish line. I tend to use a picture of an object like an animal rather than a grayscale chart since it gives me a better result. Just a personal thing I guess. The Inkscape engraving settings are shown below.

Step Three: Examine the darkness and focus. If the focus is off that position the work piece (plywood) higher or lower. Typical lens focus on these machines is 50.2 mm. When the engraving is too dark then increase the range $30 say to 1700 or when it’s too light then lower the $30 value.

Out of focus

The picture above shows the engraving being out of focus, notice the faint tree stump details with the pictures below.

Too dark $30=1024
Almost – $30=1700
Right! $30=2500

The $30 range value will depend on the quality and age of your CO2 laser tube. My stock tube that came with the K40 did had a value of 1024 for a superb picture quality as last picture above. Also some G-code senders like cncjs allow you to change the laser intensity and speed on the fly, so you can play around with it until you’re happy.

The time to engrave this kestrel bird was about two hours. Less grey scales or a lower engraving resolution will allow you to run the controller faster than 1000 mm/s. If you see stutter then it means you’re driving the controller a bit too hard!

Of course there also other ways of engraving as a young lady showed me her works during the Maker Faire. Thanks for your gift, Liliana!

Hand work

More information about the Inkscape Plugins can be found here

3 thoughts on “K40 engraving calibration instructions”

    1. Hi Jon, I will post the Inkscape plugins on my github account paulusjacobus these can be installed by dropping the files into the inkscape/share/extension folder. Also the g code generation has been adapted to suit the grbl firmware.

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