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Setting the laser power on raster engravings?

Hello everyone. First post.

I've been dealing with Paul a lot on my K40 setup and I'm running into some issues. Paul has been great with explaining some things but it's time I take a moment on the forum where we can all help each other.

The things I can't figure out are $30 (PWM max), the laser intensity setting in CNC JS, and the Spindle (laser power) reading in CNC JS.

When setting the maximum laser power via the $30 command I'm understanding the concept of how it works but in practice I'm having difficulties. I've been streaming my files using CNC JS to have more control over my projects. When setting $30 max laser power command I'll use 1500 as an example.

If I run a file CNC JS, I've set the $30 max PWM at 1500 and my laser intensity at 50%, most of my engraving is running at 100-300 power (this is in the spindle reading). So then if I change the laser intensity in CNC JS up to say 70% laser power those numbers go up to say 300-500 (these are examples, the math may not work out).

If I continue this trend of upping my laser instensity in CNC JS up to 90% and higher those power numbers continue to increase.

All that said, what I can't figure out is how to put all of this together to understand what power my laser is running at. I can increase the spindle (laser) power in CNC JS above 100% and those spindle readings are still pretty low. Even when I change the $30 those spindle numbers read fairly low but the laser power changes so it's obviously a relative change. I can also switch over to my onboard controller and set the power at 20% and it burns through the wood I'm engraving so I know my laser is not operating a high power when doing this.

In order to correct this should I be increasing/decreasing the $30 command? Should I up the spindle (laser) power in CNC JS above 100%? What about the $31 command (minimum spindle speed/laser power) should I increase this?

I know that experimenting with this will bring me more understanding of what works but I also need to understand how it works to apply what I've learned to future projects because I am currently not getting very nice engravings at all

Thanks for any tips and advice. I know this is quite a bit of information to sift through


I guess it's because the instructions say to go higher on $30 if the piece is too dark. Well going higher on $30 adds power I thought so I am having trouble understanding how going higher on power  makes a dark piece lighter.

I'm testing an engraving with a high range of grey and I've tried $30 setting from 500-1500. They all cook my wood if the laser power setting in CNC JS is above 60%. There is some difference though and when I change the laser power in CNC JS it feels like it is in relation to the $30 command. As in, if my laser power is at 100% it's not actually 100%, it's 100% of the max power set by $30. If that's the case then I still don't know exactly what power I'm engraving at, I just know that it's less or more in relation to everything else.

So, if I am engraving at $30=1024 and lowering the laser power in CNC JS to 50% gives me better results, in my head I should go $30=512 and run the laser power at 100%. However, it's not working like that I don't think.

Hopefully that helps better describe what I'm getting at. Since I'm confused by these settings it's difficult to accurately state my question

As I learn and understand stuff like this I continue to post. Just in case the next guy googling around comes across.

So, at this point, what seems to be happening is that the laser power control in CNC JS is always changing in relation to the $30 command. I don't believe having the laser at 100% in CNC JS is actually running the laser at 100%. You can actually change the laser intensity to above 100% in CNCJS so I'm convinced it is always changing in relation to the $30 max power setting. Someone PLEASE correct me if I'm wrong.

Original question still applies: How do I know what power level $30 is setting my machine at? I think I may need to test this with a multimeter but I'm not 100% sure of the process. Maybe set the $30=X then do a test fire from within CNCJS and check my multimeter? AND Why does increasing $30 make an engraving lighter if it is giving the laser more power?

The greyscale image I was testing was VERY light and the preview looks good but I have not been able to create a decent engraving from it so I've moved on to something that has more harsh grey variation. With $30 from 800-1000 so far I'm getting beautiful output and I couldn't be more pleased. My current project then will be to learn how to make the machine do very soft grey shading and variation per the image I'm engraving.

Attached are some images of what I was trying to engrave. Just a random LIGHT grey test image at 50mm. I obviously could not get the light areas to be engraved. Maybe I was expecting too much and I should have been at a much higher power. Maybe the blacks really do need to be sunk in and I wasn't giving it a chance to do so because I was expecting a much more light engraving process?

Uploaded files:
  • rasterfile.gcode_0003_Gray_256_preview.png
  • 20180525_152931.jpg
  • 20180525_152936.jpg

Think I got it. Using CNCJS:

$30= max power I want the laser to receive from power supply.

Laser intensity (within CNCJS) = power laser receives based on $30 command

Spindle readings (while engraving) are a percent of $30. So if $30=1000 then a spindle reading of 100=10% power. $30=2000 then spindle of 100=5% etc.

The issue I've had comes with the actual spindle readings in CNCJS while engraving. I couldn't seem to affect them directly. I believe they are the "greyscale" that is set somewhere in the inkscape plugins. So the inkscape plugin interprets the greys it sees as a percentage of power. So when I'm changing the $30 command up or down I'm just making the laser power a different percentage of $30 based on what the inkscape plugin has already set.

It's like an inadvertent change. Within the Inkscape plugin there are settings like offset and compression, maybe these will affect this to some degree. The reason I've had such an issue with this is that those spindle readings while engraving are always in the same basic range. Around 100-300. I've been wanting these readings to be in a much wider range thinking it would give me more grayscale. $30 gives me a wider grayscale to work with but if the Inkscape plugin is always using the same range of power (i.e. 100-300) then I'm not actually giving my laser much more grayscale to work with. I'm just making the entire image lighter or darker.

If I am incorrect in my assumptions please let me know.

grey offset and compression settings explained



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