Over size cutting and under size cutting all at once what the heck ?!

I wanted to make a template for engraving some dog tags. I drew up the dog tag on a red layer and cut it out with my co2 laser. I fine-tuned it till the actual dog tag fitted nicely inside the cutout. I created a grid of 5 columns x 2 rows and then drew a rectangle around it. I proceeded to cut that template expecting everything to stay the same (in size). After taking out the cut piece to double check the size, I found that it was an entire 2mm width smaller than the original test I did, yet the dog tag hole was bigger than the original one.

I then selected “cut selected graphics” selected a single dog tag cut and tried again. This time it was perfect.

I did this a few times and found that if I increase the kerf, it over-exaggerated the problem.

The layout I am using

The difference in since between cutting a single and cutting the entire template.

The smaller one with the big hole is from trying to cut the entire template
The larger one with the small hole is just cutting a single selected one

This is happening on my machine with Ruida RDLC320-A. I have tried it on my other machine using a Ruida 6445s and works perfectly.

Here is the file I used:
Dog_Tags_Template_Test.lbrn2 (30.2 KB)

Hope you guys can help.


I think what’s happening is that when you cut a single dog tag that the kerf is being interpreted to be an exterior cut for the outline, and an interior cut for the hole.

When you’re cutting all of them at once, the reverse is happening because you added the outline cut around all the shapes. So the outside of the dog tag is now being interpreted as an interior cut and the hole an exterior cut.

yeah, it’s clearly doing something wrong on that one machine, I have updated the info above.

What is strange though, if I change the outer rectangle to another layer or even a tool layer it still does the same thing.

That breaks my hypothesis unless this is a bug.

The fact that the behavior is different between machines is very odd.

Are you using Start or Send to run the job?

Can you upload the .lbrn file here for review?

Thanks for replying,

I have updated the original post with the file.

I’d like to make sure I understand the exact circumstances of this. At first glance looking at the design my original hypothesis seems to hold.

I’ve increased kerf to 5mm to exaggerate the effect. I’ve also ungrouped the dog tag at top-right as that was making that one behave differently than the others.

This is Preview with the outside rectangle. As hypothesized, because the dog tags are now embedded within an outside rectangles, the outside of the dog tag is considered an inward kerf, and the hole now an outer kerf.

This is Preview with outside rectangular line removed. It treats outside lines as outward kerf and inside lines as inward kerf as you’d expect. This is in contrast to what you indicated so not sure what the difference could be.

Now the other mystery is how these could possibly be behaving differently between two lasers. The kerf offset is managed in LightBurn before ever being sent to the laser so they should be getting like for like RD file content.

Can you confirm the following:

  1. You are sending to both lasers from the exact same computer and design
  2. You are using Start button to send the files, not Send. I’m trying to sort out if there’s potentially a file caching issue going on.

I have one machine standing between the 2 lasers which I send the jobs from.
I am using the start button in both cases.

if I use the orange T1 layer for the outside rectangle, I get the same result as when using a red cut layer for everything, it does not make sense to me at all.

if it was all the same cut layer I agree that what you explained makes sense, even though I don’t agree on how it should work.

I would honestly have preferred out being out and in being in and not having to worry about what the heck Lightburn is going to try and do to it when you start nesting.

I generally use a red layer for everything with an outward kerf and a green for an inward kerf. This has never been a problem for me (that I have noticed until now). Maybe I just never really noticed it, but then there’s the problem of it behaving funny only on one machine.

Can you take a screenshot showing this? I’d like to compare to see if anything is different from my setup. I can’t recreate it.

How would LightBurn know what your intentions are in terms of what is intended to be a hole and what is intended to be an outside line?

Does the problem show in Preview when you switch between lasers? Or is the difference only in the output?

And to confirm, you can be in the same design, pick laser 1, run the job and have this issue, switch to laser 2, run the job and not have this issue?

seems like I was mistaken it does not do it with the Tool layer on the outer rectangle, I was very sure it was doing it.

anyway I found a way to get it to work as expected grouping them each on their own prevents the issue I am having

With Tool Layer

with red cut layer on outer rectangle

I noticed this as well but wasn’t certain if it was intentional behavior. Seems a bit fragile and easily missed.

But if it works for you then that’s great. At least it moves you forward.

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