Engraving Quality / Laser frequency questions

[Bryan Cope]

Engraving question / tuning question.

I’m getting these strange patterns in my engraving. It seems like the frequency or pulse rate is wacky.

I’ve seen people mention EMI and vibrations being a contributing factor to poor engrave quality, but really don’t know what that looks like or what causes it. This seems to be an ignition timing problem.

When I run at higher speeds it’s very noticeable that the edge of the engraved area isn’t getting a good full blast of the laser. At 100 mm/s it’s less noticeable, but at 200 and above you can see it. I have already adjusted both the mechanical backlash and reverse offset engraving / offset repay settings.

I have attached pics of my setup and examples of the poor engrave. You can see in 2 of the photos that my engrave doesn't meet the edge of the vector and the faster I run the machine the more evident the power ramping issue.

[Jeffrey Aley]

According to "The Russ Formula for Successful Dithering", it takes his power supply about 3 - 4ms to produce a full-power dot. Given a spot size of 0.2mm, that means that you can't run faster than 67mm/s if you want absolute precision. Most jobs don't require that level of precision (for example, your pictures look fine to me, with the exception of the magnified ones), and therefore can be run faster than 67mm/s.

I have heard that some power supplies are much slower than others, so perhaps you have one that's particularly slow to respond.

[Bryan Cope]

I’m wondering if the wiring is just junk and needs to be redone. The delay in firing is preventing me from doing detailed engraving. Someone suggested I find the rdv and rdu files and that might help calibrate the controller to the PSU.

[Gene Uselman]

Those files are here- viewtopic.php?f=104&t=3459

[Jeffrey Aley]

I’m wondering if the wiring is just junk and needs to be redone. The delay in firing is preventing me from doing detailed engraving. Someone suggested I find the rdv and rdu files and that might help calibrate the controller to the PSU.

No, it's not the wiring. It's the rise time of the voltage from the power supply. This is not easy to measure safely because we're talking about thousands of volts!

See Russ' last videos on "Curtains". Smoothing out the mechanical stepping would help because it would mean that the head is moving at a more constant velocity and not speeding up and slowing down with each tooth in the belt.

But to be quite honest, I think you're expecting the laser to do something that it is not capable of doing. If engraving quality is paramount, then slow down. See also Russ' videos on spot size and DPI.

If you discover a way to improve the quality, please share it!