Dialing in the low end for engraving

Machine: K40 Nano M2
Board: LaserBoard
Firmware: I have a new board and I’m using whatever it came with
Software: Lightburn - gcode version
Problem/ Question:

Hi Forum,
First many thanks for such a great resource. I sincerely appreciate all of the contributors. I will advise that I am a complete noob, having just stood up this machine about a month ago, having spent every weekend and many evenings with it, and enjoying every minute spent.

I’m interested in dialing in my machine a bit for engraving; birch and acrylic mostly and I use a lot of chipboard for test runs. I’ve been surfing and reading many posts, running several tests (ramp test, standard testers), and am happy to provide additional info as needed.

I realize settings will change based on media and machine, but I’ve noticed some oddities with my K40 for which I’d like some advice/direction.

Here’s my machine, so you know which K40 variant I have

Power, enable, and test buttons and most importantly, ammeter.

And my laserboard; ribbon cable on the y-axis variant.

I noticed that my “engravings” using greyscale were not offering much variance, somewhat akin to what I found in this post, with similar results on both clear acrylic and chipboard.

After reading that post I did a few things.

First, checked the response to %s of the power setting

  1. Set the pot to 10mA. (test fired to home in on 10mA)
  2. Via Lightburn, entered GRBL commands to set to mm, pick a spot, cut a 10mm line at 10% power at F600
  • G21
  • G0 X0 Z0
  • G0 X0 Y10
  • G1 X10 S0.1 F600

With this I noticed that the ammeter on my K40 seems to be run quite high relative to power %. With these settings; 10mA / 10%, that line cuts at about ~4mA, at 20% it’s ~5mA. In fact, issuing and monitoring the commands from this post, the ammeter pegs quite high across the board, topping out early on the high end at 70%-100%.

I didn’t expect the output to be linear, so went poking around a little more and came across this article (which is a doozie) and that’s where i read (vs learned) about the complexities of PWM frequency and how it might be adjusted. However, even with a PWM setting of 400, the ammeter still pegs at about 3-3.5mA at 10%, 4-4.5mA at 20% with the pot still fixed at 10mA output.

So to explore a little further I did a few more experiments to get a better sense of things, this time with the pot at 10mA, speed of 50mm/s, and power settings between 1% and 5% (from comments on that 1st article), looking at two variables (independently), PWM [200|400] and DPI [254|400]. The results are interesting but raised more questions.

First, you’ll notice that the media is card stock. I picked it because it’s white and would show any marking better than birch or chipboard.

On the right, there are two groups of 5 experiments, 1% to 5% of 10mA, at 50mm/s, 400pwm, 400dpi (top) and 254 dpi (bottom). There are a couple of okay gradients there (e.g. 2% 254dpi), but more questions than answers.

  • At 1% in both test sets, there are few if any shaded cells and interior lines.
  • In each case, there are a number of cells that were never touched. They’re completely devoid of any markings. Even in the 10mA, 50mm, 400 pwm, 400 dpi, 5% case, there appears to be room for additional gradient, but none exist in 4 of the cells. It appears to fall off.
  • Also, as the power decreases, these void cells increase in frequency. Makes some sense empirically, but I expected a uniformly diminished gradient over the entire area with a power decrease rather than an increase in absence of engraving. I think the net is the same, it just didn’t manifest as I expected. It seems like I’m hitting a power floor/cliff that results in a full drop in output.

On the left, there are two groups of 3-4 experiments (I didn’t do the later ones as they were just burning up the media), 1% to 3/4% of 10mA, at 50mm/s, 200pwm, 400dpi (top) and 254 dpi (bottom).

  • At 1% in both test sets there is absolutely nothing, the ammeter barely wiggled at all.
  • Again as the power decreases, these void cells increase in frequency. More dramatically though, there appears to be vary little variance.
  • In this case with the PWM at 200 the media is really just burned up, with very little opportunity for a gradient. In reality I’d rarely if ever use this for media, but it is interesting to note the effect of a 400 over 200 pwm setting all other things being equal.

So my questions are these.

Am I on the right path? How else might I make adjustments on the low end?
At 10mA and 10% the ammeter registers ~3-3.5mA, even with a PWM of 400. From what I’m reading that seems high, with an ideal of around 1mA. I’m not expecting perfection/absolute linearity, but want to understand this response and anything else I might do to drive it lower, perhaps additional settings. Thoughts/Suggestions?

It also appears that there is some power threshold below which results in zero effect on the media as illustrated in just about every case. I think that’s obvious, but I’ve also noticed a minimum power % setting for a layer. Wondering if that might at least bookend the drop off? Thoughts? Anyone use that setting?

Any other suggestions are welcome.

I’ve also provide my device settings here:

And the settings of the last sample that I engraved for reference.
10mA pot, 3%, 50mm/s, 200 PWM, 400 dpi

Thanks for your time.

We’re working on digesting the entire content of your post (lots of words, yay, but in a good way), but the short answer is to bring the pot value lower.

10mA to 15mA is a good general purpose value, but not by any means the lowest value. If I’m doing work with paper, I’m bringing the pot down to 1-2mA and then adjusting the % in LightBurn accordingly. In fact, I know several people where those were the 2 marked positions on their panel: 2mA and 12mA :slight_smile:

Your first process is on the right track. Set the pot and do a test fire to make sure it is at a certain value. Then do a line at 100% power to see that you are still at that value. Then play with 50% and lower to see what actual values you are getting.

Hey Ray,

Thanks for the reply. I realized that it was a lot when I posted; it was late, I over compensated on the info, and frankly, no one’s ever called me terse. :smiley:

Been a busy week this week but I have been noodling on it and came to a similar conclusion… if I can’t further manage the power distribution, maybe I could translate it downward by adjusting the overall power. Will play around with that this weekend and see what happens.

Was very thankful for the article on PWM. There’s a noticeable difference in this device with that adjustment. Thanks again for the reply and hope you and the team had a great Labor Day.


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I mean, many of our support inquiries consist of 2 sentences fragments, so this was a welcome change from that :slight_smile:. I do best with digestible chunks of the right amount of information with simple words. The stuff that I saw in your post was a good place to start and it sounds like we’re on the same page for the moment

I did my first trad lead climb outdoors last weekend, so considering the anxiety associated with 1 misstep resulting in a large fall and spinal injury, it went well :slight_smile:

I think Starla got some good time to relax also.

Hope yours was good as well.


Thanks again Ray,

A big wow on the trad lead climb success! I had to look it up and that is not a sport for the feint of heart. Many years ago I did some climbing inside some old converted grain silos and that was enough for me to know that its not my thing :slight_smile: These days my hands sweat just watching videos of people climb. Congratulations and I wish you continued success and great adventures.

It was a productive weekend and I was able to do a fairly decent job of getting a nice gradient across some chipboard. Two things really helped.

  1. Reduce the power. As you suggested, I used the line cut tests at various low amperage to figure out where my K40 responds best, e.g. pot at 2.0, 2.5, 3.0, 3.5 mA, … and then power at 1,2,3,4%… of each setting to see where the best visual response was. Worked well and produces a nice response curve.

  2. Use dithering, not greyscale. It finally clicked for me after noticing the tool tip in Lightburn that greyscale isn’t nearly as effective with a K40/CO2 laser. Greyscale sampling translates into burn depth/intensity and while it can create a small gradient, materials will saturate at some point, i.e. burnt is burnt and it can’t be burnt any further, so at some point there’s little to no visual difference for a given material as the power increases. What’s needed instead is dithering to manage the burn/pattern density in order to create an analogous visual effect. So a quick switch to Jarvis or some other dither pattern yielded the desired effect. This makes sense to me now.

Again, many thanks for your support and for building the community.