I decided to make a black box that will shield my experiment from unwanted light. Because it's going to be press fit from 3/16" cardboard i first needed to find out what was the slot size that would be big enough to fit the cardboard in the slots and small enough to be stable. So I designed a comb with varying sizes of slots to empirically test different sizes in one go. I used Inkscape's clone function (laser cut comb) with a slot the size 3mm and 20mm height cloned ('create tiled clones') 17 times with 3% change in width each (and 100% shift).
It turns out that a slot of 3.75mm is great (well in retrospect something of the size 3.85-3.95 would be better) so i designed a standard notch that i used for all parts.
Here are the parts:
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