Hmmm...I don't recall my tip to focus but...what I do (for now) is actually burn a one inch line into my 3mm ply and see how thick the line is. I do this manually sending gcode. Then I vary the focus and repeat. I keep track of the focus ring position and when I see the smallest line, I know that's the sweet spot.
Some notes about this:
1. I made the PWM mod described elsewhere in this forum so I can control the laser power (thanks to @Zax).
2. While you can just set power to 20 and turn the focus ring and set the focus, I personally don't like doing it that way, thus my writing gcode and burning a line to get the smallest line possible.
3. I'm going to be making my own focusing ring soon and it will have calibration tick marks on it so once I set a focus, I can repeat that setting for my 3mm ply. I have a 3D Printer and I have the focusing ring design 90% finished, but am still tuning my 3D Printer. I expect to be able to print it and test it very soon. If others are interested in this focusing ring, I will make it available.
