Poor Contrast in Grays - Before and After Laserboard Install

Machine: K40 6C6879-LASER-M2: 9

Board: Laserboard

Firmware: Smoothie

Problem/ Question: Hi, I’m having trouble getting a decent contrast on anything photo/grayscale, etc. Shown in photos is RASTERIZED, Grayscale so I could run it in Grayscale mode. Settings used are in photo engraved on it as well. Any suggestions? Is this typical and next step going to the other GRBL-LPC firmware? Any help is greatly appreciated! Thanks

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It can take some tuning. Some people have changed PWM frequencies to get better results. For me, I found that a minimum of 0% and max of 5% worked, but everyone’s system is different.

Oh wow, that little of a range? Interesting. Not sure how to change the PWM frequencies but I’ll check around. Thanks!

I found the write-up and will see what happens. Thanks again!
https://forum.cohesion3d.com/t/pwm-tuning-for-smoothie-firmware/99

That’s one example. Be careful though, if you start hearing screeching noises, it’s very hard on the power supply and you should change it.

OK got it. Good to know!! Appreciate it.

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I tried changing laser_module_pwm_period 200 to 400 and don’t think it made much difference. I have tried just straight dithering and lesser resolution along with less power and speed. From where it looked “best” I varied only one thing and tried a bunch of iterations. In the end I feel like I’m only able to get like 50 gray levels vs 250 relatively speaking (no matter what setting either among dither types, grayscale, newsprint). Do you have any suggestions? Do I play with that pwm number somehow? There wasn’t any screaching after changing to 400. Thanks!

How fast are you going? I’ve also found that to get good contrast, you may have to really slow things down. I know if I go fast, it just vaporizes the heck out of the wood instead of turning it dark.

Did this with Newsprint at about 50mm/s and 1000dpi I think it was. (been awhile, I don’t often do photos.) Done on baltic Birch.

I’ve tried ranges from 200ish down to 50mm/sec. Of course then having to adjust all other variables once doing so. Still just “flat” in the contrast it seems to me. Running more tests now with just small tweaks to see. Maybe I’m expecting too small of a dot from this machine…

Wow - that looks really good. Around what size was that? Few inches wide?

OK Here’s some progress I’d say…
Super slow of course but looking better. I never went above 5-600 dpi thinking it would try to put too many dots together and just plug up the grey areas. I think the slow speed and high density setting is helping because it’s causing more burn not scanning by so quickly like you said.

  • Machine knob @ approx 5 ma.
  • Speed 50 mm/sec
  • Power Level 5% MAX
  • Interval 0.025 mm (1,000 dpi) Newsprint Mode
  • Material: 30 mil Chipboard

I think that was done on a 4" x 6" sample I got from Amazon.

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How are you processing the photo beforehand? There are a few steps that helps, like adjusting contrast, sharpening, using unsharp mask etc.

All thru Photoshop. I have tried everything from levels to curves, all different filters, etc.

That last one did look like it was going to be a lot better than previous tries.

Yes - it absolutely did. However that tactic didn’t work on the acrylic since there is no dark and darker…

Dialing in for birch and acrylic can be a pain. Here’s where I live, 3mm acrylic using the grayscale setting. I didn’t try to improve this, which I’m sure I could with some tweaking.

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Got it. At least I can see what’s possible and go from there. Thanks!

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