3 mm vs 1/8 in material

I see 3 mm and 1/8" being thrown around interchangeably. For the most part they are, but I’ve purchased designs from Etsy a few times in the past (specifically board game box inserts) where slots are made in the stock to accept tabs to make trays and boxes. For external finger joints this isn’t an issue because the thickness of the stock doesn’t come into play. For internal slots, the extra 5% of thickness that 1/8" has compared to 3 mm causes the tabs to not fit. I have to shave or file down the tabs or the slots to get them to fit.

Has anyone else had this issue? I figure my solution is to buy truly metric plywood, but I see so many stores using 3 mm and 1/8" interchangeably that I’m not sure where to buy.

I’ve had enough trouble with anything I’ve purchased that I just assume I might have to slightly modify the design to make it work. I figure I’m paying for the intellectual property and 90% of the implementation.

Even if it’s perfect, I think there’s enough variation in natural material that something that works one day, on one batch, may not work the next.


One way to deal with that is to size up/down the entire design that 5%, as long as that change in the finished product doesn’t bother you.


When slot dimensions can come into play, I measure the material and adjust the design.

I have used both acrylic and plywood (much from Glowforge) that were nowhere near “stated” dimensions. Acrylic even varies from one end of the sheet to the other, if you want to get super precise.

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Do you mean modifying the file or modifying the physical glowforge output?

In theory I like this solution, but in practice I think the error stackup could get out of hand. A typical box is on the order of 10", so the 5% change (1/2") there could cause for a lot of slop in the box.

I’d still like to try it out and see how it works out in practice.

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I’m talking about correcting the slots/tabs, not the overall size of the design.

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Same as eflyguy.

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This is the best advice out there. Couldn’t agree more.

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I have purchased a few files on Etsy that the designer included a little test cut so you can make any adjustments on that until you get the fit you want.

I’m not sure why I had it in my head that the design / file was a strictly holistic entity and the parts unchangeable without changing the entire thing. I was able to change just the thickness of the slots in inkscape and it worked out fine.

Thank you.


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