Cut Shapes Move themselves

I have the following shapes and want to cut.

Everything looks okay, for now. But after cutting it automatically moves the blue shapes upwards??

All I did was click cutshapes…

Now its not aligned? The blue shape is now outside of the border I created. Its more apparant after removing the cut shapes. What am I doing wrong?

Heres the file.

Bar Key Carlos.lbrn2 (26.3 KB)

I can’t quite tell where in the design you’re doing this or what you’re cutting with.

One thing I can note is that when LightBurn creates new shapes from a boolean and I assume cut shapes operation that the resulting new edge may be slightly shifted or different from the original shape used to make the change. I assume this is from a rounding error or other approximation of some kind. I think I remember hearing that operations are done at either hundredths or thousands of a millimeter but don’t take that as gospel.

You can demonstrate the phenomenon by subtracting one shape from an other and then trying to union back the original subtracting shape. It won’t result in a complete outline of the original shape.

Based on your screenshot it looks like you’re describing a shift in the hundreds of a millimeter which would fall into that type of change. Again, can’t quite tell what I’m looking at from the screenshots, however, so tjhis may not be what you’re seeing.

255.8 in the design, I made the screen shot big enough to see where the operation is happening.

Trying to remove everything outside of the rectangle. Basically open the file, click the blue layer, then click the black rectangle and choose cut shapes, it should auto select the stuff outside of the black rectangle. After the cut the blue shapes are moved slightly upwards, its in multiple locations, just zoom in. Once zoomed in click ctrl z to go back and see what it looked like before.

My laser operates at least with .1 precision and maybe more like .08 so this would show up in the finished piece… Suprised this happens since this stuff seems to be so exact. But I guess not?

I would like to use the mask but then Lightburn has an issue where it will try to frame the hidden portion of the image. SO thats why I use cutting now. Gosh so many little gotchas with this software. I have a thousand notes… and only find more.

it definelty moves the blue layer upwards, heres the bottom…


I don’t think this is likely to be noticeable in any way. From what I can see the difference in position is .003 millimeters. You probably have 10x variation in that in a single burn line.

You can avoid that if you flatten the image mask.

I’m not familiar with any software that does not have a limited floating point approximation. If you do the boolean test I described in other software, are you familiar with any that can recreate the original shape?

It may only be because you can zoom in so closely that this is an apparent issue. If you’ve done any CAD work there’s a concept of “CAD goggles” where your sense of scale gets out of whack since you can just zoom into tiny details. Or in the reverse where there’s no sense of size when zoomed out.

If you’re uncertain about this I’d encourage you to run some tests to see the level of tolerance you have to work with. Keeping in mind that every software in the world is rounding things. Be aware that even your controller is rounding things once LightBurn commands it. It’s rounding all the way down the entire chain.

When I open your file and proceed as you instruct, I measured 0.0001 inch or around 0.003mm shift after cut. This is not unexpected, as @berainlb suggests.

But that doesnt explain why the left and right side would be perfect?

Left side

Right side

Here is what I get using the same steps.

How did you produce what you are showing above?

Open the file, click the blue layer, then ctrl click the black rectangle and choose cut shapes, it should auto select the stuff outside of the black rectangle. Delete the autoselected blue layer, should be the outside stuff of the rectangle.

After the cut and delete the blue shapes are moved slightly upwards, but check the left and right side, they are perfect.

Heres a video of what I see.

The left and right are perfect but the top and bottom are off, it’s moving upwards somehow. Probably just the CAD goggles but you think it would do the same thing your talking about universally. Something odd here…

Further more I can manually align the layer to be perfect with the black square. So the boolean doesnt appear to be off, just as mentioned its moving the shape upward.

Hmm even after a flatten it acts weird, guess another quirk because I had rotated this. See this

Yes indeed. That’s to be expected for rotated images. No direct way around it within LightBurn as far as I know.

As a workaround you could:

  1. rotate image
  2. File->Save Processed Bitmap
  3. Apply mask to selection
  4. Flatten image mask

Did the higher powers figure out why the shapes move up? I understand I have my CAD goggles on but as I have demonstrated above, the explanation given above is inaccurate to what is happening.

The left and right sides are fine so whatever about the booleans would have happened there too, but it didn’t and that shapes move up…

Still awaiting some kind of response on that.

Yes there are many quirks, after using GIMP and Photoshop I have learned this program has its own behaviors. Like it somehow remembers the photos rotation after a flatten. Lol

Move the cutting shape over left or right by a fraction of a millimeter and repeat the boolean. Do you get the same effect? If so, again, I think this is likely a rounding issue.

I don’t that’s why I keep holding on to this thread. I’m sure in the grand scheme of things it doesn’t matter as I have noticed far worse things with the program but just finding it odd the explanation doesn’t fit the problem. I would love to trust the software but as I’m still a noob I check but verify for almost each and every action. Which is how I stumbled upon this.

This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.