Overcut does not work with Dot Mode

I suppose you’re right about this for a sufficiently complex and high density image. My initial thought on extra verbosity was with regard to the resolution involved in this. Let’s say you were making incremental movements between drilling operations of .1 mm. But that would put it squarely in the range of typical DPI for images so if an image had sufficient grayscale variance then it should be comparable.

So I guess we just need to prove it out.

Darn it! I did some more testing and I see more about how laser cutting works.

Overcut doesn’t really resolve anything. It would need to slow down at the end of the cut. Going over just places the gas lance at the start point. Possible to compensate with a parameter change, but not Overcut.

I’ve done an initial proof-of-concept for this on g-code. I’ll publish my findings in a separate topic later today.

what about using perforation mode?

Perforation mode is inherently different, at least from what I understand of the dot mode. Perforation mode literally just breaks the line into a staggered line. Nothing else changing. Really it’s just the normal line mode with a discontinuous line.

From what was described here it sounds like Dot mode is literally just shooting the laser in one spot for a set duration and then moving on, then repeating. It sounds more like making a bunch of holes with a drill around a shape in order to cut it out.

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It reminded me of this video on 3d images in glass. They claim it’s not a vector but a dot layout where it stops and fires… Most of it you know, but about 3:40 in he starts talking about the ‘dot’ technique…

May not be anything…


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Can you not just modify the artwork so that the start and finish points are extended outside the cutout part?

Hello, maybe this is something that can be done in “Image” mode, where there is already a series of dots? Couldn’t you just create a line or square etc. and somehow change it to an “image” and use maybe a “Threshold” value to simulate dot mode?

I am old school NC programmer (before CNC kids) with paper tape et. al. where SIZE definitely MATTERS. A program these days would fill a room with paper tape, but that is no longer an issue.

@berainlb The G-code generated for images in LightBurn is HUGE compared to what was practical in the past, but we have more than the 64k to play with these days.

I accidentally found out that using an image you can burn through thick media with a proper threshold setting. I am excited about using a dot mode for deep cuts and am impressed by the work in this thread! Props to @Dannym !


If you could use an image and use pass-through this might work. Not sure to what level of resolution you can get with this method but could use some experimentation. What I don’t see this getting you is the fine timing control of the individual “drilling” operation.

If you have a chance, I invite you to take a look at the new Topic where I’ve created a POC for this.

Would be happy to get your feedback. I had a chance to do some experimentation with this earlier this week but haven’t yet published my findings.

The code necessary in my POC to cut a 10 mm square is over 1600 lines. Quite verbose.

If you are refering to the memory required, it’s really how much computer memory or disk space you have.

Most grbl controllers have a serial data stream from the computer. They usually only buffer up a few lines in the command buffer.

I’ve seen many MB files for the grbl machine.

Saw one recently that can store up to 4 Mb on the controller. Wonder what happens after that…?

Good luck.


Could an image file of a line or square etc. use 256 levels of “burn dwell” from a greyscale image in Image Mode to simulate dot mode? Like white is 0us and black is 1000us of dwell? Just a thought.

I don’t know what Ruida limits are on file size, but for example, I can send a 300gb+ file to my Arduino laser cutter from LaserGRBL on my Raspberry PI4, but couldn’t even imagine a need for a file of that size (but never say never).

Not sure what you’re referring too here.

There is a dwell, I’ve see, but if I recall it’s mainly use to delay the start of something, not the end.

Try this thread. It might answer that question…


‘Drill Mode’ in galvos works this way - it moves to the pixel center, then turns on the beam and delays for X milliseconds, where X is variable based on pixel darkness.

Dwell is used in canned cycles such as G81 and describes a pause in a canned cycle. I see GRBL does not support G81, so it needs to be done another way.

G4 Pxxx is a dwell in GRBL.

but won’t that cancel the previous command?

Which command? It’s a pause, so if you turn the beam on with G1 Sxxx and then dwell, then turn the beam back off again. We use this already for cut through mode.

Holy sh**, pardon my french, but I didn’t realize “Cut Through” was there. That is basically a “Dot Mode” is it not?

@jerdweez Take a look at my POC. What @LightBurn is describing is precisely how the POC works.

Cut through only works at the start and end of that layer’s operations.

@LightBurn Are you open to bringing that “Drill Mode” to GRBL as well if this proves useful?

Well, if the GRBL guys include G81, it has a dwell and a Z value also for deep drilling