focus and pixel size issues
after rigorous testing we are still having trouble getting a good focus. We have a Chinese made K-III (IIRC) and in general cutting goes quite well. However, engraving acrylic is our main job.
We added an low-pass filter between the PWM output for a smoother power control since the machine doesn't seem to have a low-pass filter. But without a scope we can only rely on simulation and some measurements made by a voltmeter but the results look OK now where we used to have interference issues. Maybe we ought to get back to the potmeter that shipped with it?
Is there a good way to test the focus? We tried the move up-down technique but when we go up or down with the platform (240V normal motor) we have to powercycle the machine since it crashes the cups hardware :( Should we use a very laser-insensitive material? It seems like around 23 mm is about the right position for perspex, but its an odd number.
Our pixels are not super, they are much bigger than with the old Chinese hardware on the same material. We blame this partially to focusing and/or dirty optics but cleaning them doesn't solve the issue.
We also got pixels that were `half'-pixels in that surrounding pixels were fine but a lone pixel is at times not marked correctly. We get better results when we slow down the engraving speed to say 40%.
We have several theories:
- Could it be that the CO2 laser can't switch fast enough? But why was it better then with the Chinese hardware? Could it be laser-aging? So we get less good results than when it was new?
- Could it be that the opto-coupler can't pull the laser enable line down fast enough? This would account for the half-pixels disappearing at slower speed, but not for the laser point size at slower speeds; that doesn't seem to be changing.
Any feedback would be much appreciated!