How to nest 2 or more pieces?

Hi
I’m not sure if this is the right place to ask this question, so feel free to move it if necessary…

Do you have any recipe or hint on how to nest two or more pieces (acrilyc in my case) ?
I have done it by trials and tests for this:

Obviously, there are 2 different pieces of acrylic. I made a model on RDWorks, which contains the shape of the transparent part at 100% size, and the shape of the black cat with 101% augmentation factor, to take into account the width of the laser beam.

Initially, as the shapes are not convex, I wasn’t expecting good results, but it worked quite well. The black cat fits well in its nest.

But it’s only 2 parts. I’d like to make one with 3 parts that “interact” all with each other. So maybe one at 100%, one at 101% and the last one at 102% ?

Did anyone try this and how did you do this?

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Looks good. If I understand this correctly you want to nest multiple pieces, like eyes maybe for the cat or even nest the circle in something larger? If so, you need to look at exactly how much was the difference between the cat outer cut and the black inner cut since it gave you a good fit. Like say if black cat was 0.2mm bigger than the one cut in clear circle then you need to size things so they all keep that 0.2mm difference. Percent scaling from different sizes will produce different size differences. Hope that is clear enough :slight_smile:

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I would think that rather than scaling, you would want to inset/outset individual lines to account for the laser kerf. Scaling might sometimes get you close to that but won’t be the same thing.

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Ned : It’s a bit more complex than the cat’s example. I tried to explain it saying ‘3 parts that “interact” all with each other’.
A drawing is worth a hundred words…

Thing

If I take for example the red rectangle as 100% reference and I make the green ovale 101%, should the blue diamond be 102%? Or blue 101% and green 102%? Or other settings?

Michael: I guess you’re right, but for complex shapes as the cat (or more complex ones), it can be a burden. Is there any software that could do it automatically?

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I would have thought this would be reasonably easy with inkscape and linked offsets, but apparently the only way to set a precise offset is by editing the XML directly. That wasn’t at all what I expected!

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Hmmm…that’s definitely a more complex task. You would need to scale the blue and the green the same to fit the red, but blue would need to be scaled different to fit with the green. There probably is some software that might make this easy, but the only way I know to do this is to scaled the green and blue the same to fit the red but then manually edit the border of the blue to make it bigger where it touched the green.

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In the general case, you have to work out all the kerf segments, I think.

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Kerf compensation is a feature I use daily, but I am running LightBurn as my control software. If you have a supported controller in your laser, I would download the 30 day free trial and see if this would solve your kerf issues.

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Thanks Anthony
I think I have less than one week left of my 30 days trial of Lightburn. Can you explain quickly how to do this or point me to a tutorial?

In the cut settings editor you enter the desired kerf offset. A positive number makes the shape bigger and a negative number makes the shape smaller.

Thanks, I’ll have a look.
However, for the example above, if I had add a positive kerf to the green shape and a negative one to the red shape, then I would need both positive and negative for the blue shape. Is this possible?

What you are looking for is called polygon offset (or buffer). If your starting point is a DXF fle, then you can use OpenSCAD to import it and its offset command: https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Transformations#offset
It may look like scale works but it does not (for example the tail of the cat).
The amount of offset you want depends on the laser kerf. I would start with 0.15 mm.

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I hadn’t thought of OpenSCAD for doing the offset, smart idea!

OpenSCAD can also read SVG as well as DXF, but there are some caveats.

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