I am trying to design my first project with slots. I have read all the topics having to do with this and I am more confused now than when i started. I am NOT an engineer (even though I raised one). Please don’t ask me to ask him! I have what i think is a simple question. My wood is 2.5mm thick – i used calipers to measure it. What width do I make the slot for it to go in correctly? I want a snug fit but not so tight i break the tab trying to put it in. Any help would be appreciated. This design will not be resized in the future do to the nature of the project. It will only work this size.
Thanks in advance!


The concept here is called kerf correction, kerf meaning “how thick the cut line is from the laser”. Since the laser cut has a certain width to it you have to compensate to get a truly snug fit by making the cut shape slightly smaller.

So good news, bad news. First the bad: this doesn’t have just one answer. Exactly how thick the cut line is varies depending on your material and settings. This makes it hard to say for sure how wide your slot needs to be.

The good news: for most 1/8” thick materials 0.006” or 0.152mm is about right so a slot width of 2.348mm is a good guess.

And there’s the tricky part: it’s a guess. The best way to get it exactly right is to test. I like these little guys:

Anyway, there you go. Sorry it’s not a simple answer.


It varies by the specific material and requires a little bit of testing. I find these kerf gauges very helpful.


Mind blown! TY


Wow! TY

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I think I can understand this one. Lol


Yeah these are like what I use too.

The best part: you can successfully make tabbed/ slotted projects with multiple materials using these. Cut one from acrylic and the other from plywood and figure out which slots work with each other. It’s really easy to get accurate kerf corrected slot thicknesses this way.


Once I decide what my kerf is I then take my design in Inkscape and set the width of the line to the total kerf. Then using Path>Stroke to Path on the line the program makes each side of the line a line (you have to reset the line width to something small to see it.) Path >Break Apart makes everything individual objects so you now have two lines set apart by the kerf width :slightly_smiling_face:

Then you can cut the inner one to make a hole and the outer one if you need to cut something to fit inside the hole (or just delete in the case of a slot). Now whatever the shape you can have a perfect fit :grin:


Or you can forget about measuring kerf and use the serrated kerf posted by our illustrious leader @dan


I love those things…use them on many non-glue assemblies. :grinning:

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I missed that post, thanks!

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