Poor Quality Raster Engraving
I was using my K40 with K40 Whisperer to engrave simple black and white patterns into wood from vector artwork and getting great results.
Since switching to the Mini Gerbil I've been unable to get anything close to the same same quality, with edges and fine detail being lost, regardless of speed. I've tried messing around with PWM frequency since I don't require greyscale, but not sure what range I should be working in and still not getting the same fidelity.
I've wasted a lot of time and materials trying to get back to where I was, and wondering if this is just the result of using PWM rather than a potentiometer. Vector lines are perfect by the way, it's just fills where the edges are soft.
Any help would be massively appreciated. Thanks.
Hi Tom,
The difference in Vector and Raster engraving is a result of how the laser beam is used. Raster engraving uses dots, so setting the resolution low (DPI) will result into artefacts which can look rough. High DPI means slower speeds for engraving since more dots need to be used. Typical 90 or 160 DPI should be enough. Next to resolution is the used dither method, e.g. jarvis, newpaper, dither etc. Some work better then others.
Note: The PWM or analogue input signal does not make much a difference since the input signal is converted into an internal PWM signal by the Power supply. If the IN pwm has a freq. at say 60 Hz then yes there are a lot of dots since it is not seen as a continuous signal but as dots. At a PWM freq. of 250 up to 1500 Hz, there is no difference.
So you could use vector images instead which gives excellent results or combine vector and raster (e.g. use vector for outline and infills with raster). USe 90 DPI in Lightburn or other Laser applications and use jpegs or BMPs that have good resolution and no internal pollution (artefacts, hidden information). Often taking a screen shot and saving it via a photo shop editor program can help to fix weird dots that pop up in the engraving (due to hidden info).
Using lasers and getting good results are an art and lots of use gives you the experience and knowledge. Getting your laser to know is a long process and after a few years I am still having a sample go before committing a piece of wood.
Cheers, Paul
Thanks for the prompt response Paul, and for clarifying the PWM issue.
Sorry, my post title is a bit misleading. I'm working from vector illustrations, which K40 Whisperer was rasterising at 500DPI and I was engraving at 300mm/s, although my most recent experiment was to rasterise before importing to Lightburn.
I've tried every conceivable combination of DPI, line interval, speed (Lightburn and $ values for max rate and acceleration), power, PWM etc, both working straight from vector and from a high quality pre-rasterised image, and the results are always soft, with fine detail skipped altogether in places.
Interestingly the results seem to be better on acrylic at higher power settings, so I was wondering if it's just the way the PSU interprets the PWM signals for low power.
As a sanity check, I put my Nano board back in yesterday and tried the design through K40 Whisperer and got excellent results again.
I've also been getting the same homing problem that several people have mentioned on here, where it hits the back stop then stops. This happens every time unless the head is already to the left, but worked perfectly with the Nano board installed again. I've got mechanical stops and a 4mm pull-off set, and tried increasing the debounce time but won't go above 250.
Thanks, Tom
Is it possible to get some assistance with this? It's frustrating that after all the time and money thrown at this I'm back to using K40 Whisperer and the Nano.
As far as I can see there's never been a resolution to the homing issue, which is definitely not a mechanical/electrical issue since several people have experienced it and it's immediately resolved by swapping back to the Nano. I've tried playing with the pull-off and debounce values as I mentioned.
As for the engraving issue, I'm starting to think that maybe the PWM control just isn't very reliable at low levels, but I'd love to be proved wrong, because the Lightburn workflow is still very appealing.
Thanks, Tom