Getting undesired stippling when engraving using STL depth map

[rnorris (Robert Norris)]

Hi,

I’m a new user of LightBurn, and I am working on engraving some novelty coins on a 30W fiber laser. My issue is that there appears to be some kind of artifact on the lower ~80% of the engraved test object. I am not sure what the name of this artifact is, so I am having trouble figuring out what the right search term would be if someone has had this issue before. Since this artifact looks a bit like stippling, I will call it that.

At first, I thought this was an issue with my laser setup, but I have narrowed this down to the way that LightBurn is turning a depth-mapped STL PNG into a tool path, because this same artifact shows up in the LightBurn preview!

Here is the depth-mapped STL PNG:

And here is the stippling artifact:

This also shows up and is quite noticeable on my test piece. Here are the steps to reproduce this artifact:

• Download STL file from Printables
• Convert to depth-mapped PNG with STL2PNG - javascript edition
• Import image into LightBurn, set Width/Height to 37.600mm
• Create a circle of diameter 37.500mm and add it to the T1 layer
• Vertically/Horizontally center the image and circle
• With both selected, apply the circle to the image as a mask to remove the black areas
• On the image layer, set the image mode to 3D Sliced
• Open the cut preview

I have a copy of my image settings here, in case there is anything obviously wrong:

Has anyone seen something like this before? If so, is there a way to either remove it, or at least make it uniform across the entire coin? Thank you.

[jkwilborn (Jack Wilborn)]

Followed each step… except I flattened the mask also, got this in the preview…

You might do better with something that has some depth to it. This really has only two areas…

is there some reason you want the white boarder? I shrank it down to ~34.6mm.

I traced it with good results.

With all fill operation turned off…

Can’t see where your anomaly is occurring…

I don’t run with a 90 scan angle, what is this for?

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What version are you running?

[rnorris (Robert Norris)]

Thanks for trying it out!

I tried out flattening the mask, but this also doesn’t change my preview.

is there some reason you want the white boarder? I shrank it down to ~34.6mm.

The engraving area on my coin blanks is about 37.55mm. I set up the mask to be a bit smaller to be sure I clip out all the black areas at the corners, since a small sliver of those got into my test piece and ate up a ton of engraving time.

I don’t run with a 90 scan angle, what is this for?

The 90 scan angle is one of the three operations recommended for deep brass engraving for my laser on this page: https://www.lasertips.org/?search=brass

From my understanding, the recommendation there is to run 25 passes at 90, another 25 at 180, and five finishing passes at 315. I am not sure exactly how these parameters were created, but the scan angle doesn’t appear to affect this artifact either.

What version are you running?

This is what the ‘about’ menu shows:

LightBurn 1.4.04, built Wed 2023-08-02 @ 12:08

If you are running an older version, can you let me know which one it is? I can also try that one out.

Thanks for your help!

[jkwilborn (Jack Wilborn)]

I’m running one of the public beta LightBurn 1.5.00 built in October.

@rnorris

finishing passes at 315

If you’re going to use 3dslice you should probably do it like they recommend.

In your case I wouldn’t use 3dslice as there is really no depth here…

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Trace it and use the results to burn what you want to get rid of… Then you can use the cleanup passes.

Both of these were 3dsliced, but the left one could have been done with just the trace option… there was no advantage to slicing it. You can see the advantage with a 3d grayscale on the leaf.

[rnorris (Robert Norris)]

Thanks, I haven’t tried the tracing method before, so I’ll give tracing a try tomorrow.

I don’t see a 1.5.0 beta in the link you provided. It looks like they are all 1.4.04. Perhaps this beta was removed. I will also try installing on another OS and see if the slicing method has the same issue there.

[jkwilborn (Jack Wilborn)]

I thought the 1.5 version was the public beta, sorry.

This is the traced version. There is an outline to reverse the image, when filled, you make have to remove it.

This was exported from on 1.4.01. I went through the whole process again with this version… no issues…

bitcoin_coaster.lbrn2 (560.5 KB)

Do you mind posting the .lbrn2 file with this issue?

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I have the center cross lines in Lightburn turned on. I use it to center object. If the object is moved around, you can press P and it will center it.

When I created the circles… I just clicked on the center movement and pressed P to center the object… May speed up your work flow…

[rnorris (Robert Norris)]

This was exported from on 1.4.01. I went through the whole process again with this version… no issues…

The file you provided seems to have a clean looking preview. I don’t see any stippling artifacts in there.

Here is the .lbrn2 file with the issue:

Bitcoin_Engrave_Test.lbrn2 (263.1 KB)

When I created the circles… I just clicked on the center movement and pressed P to center the object… May speed up your work flow…

Also, thanks for the tip!

[rnorris (Robert Norris)]

Here’s an update:

I installed Lightburn on my Windows desktop and repeated my process from the original post from scratch. This time, the preview did not contain the stippling artifact. However, when I opened the original file, the artifact was there. Perhaps this is a mac-specific bug? Any ideas on how I could test this further?