This what the exact method I was going to suggest. I love seeing the different solutions everyone comes up with 
Acrylic has poor thickness tolerance: ±/15% for cast, +/-5% for extruded. So if you want a slot to be a snug fit you really need a parametric design and measure each sheet. Cast acrylic is not even constant thickness across a sheet.
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That’s very interesting palmercr. I received my calipers today and was measuring some cast acrylic sheets. The differing measurements across one piece made me question the calipers. I was surmised how much variance there was. Glad to know it was likely the acrylic instead.
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That’s awesome! I think it’s great that you actually put it all together!
I had to find that out through trial and error and it is maddening if you are designing for a tight tolerance. That’s when the acrylic shelving design with OnShape made a difference. I found that the edges were .21 and the centers were .201. Since I had cut the smaller sections from larger sections and these in turn were cut from a larger sheet, I never knew what to expect. So when there is a difference within the same sheet, slots and tabs are hard to design for. Now I measure all the way around a sheet to see what I am looking at.
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I found a good source of information here: http://www.pmma.dk/Acryl_stobt_kontra_ekstruderet.aspx?Lang=en-GB
I was investigating the thermal expansion, which is massive. I left 2mm gap between 1.5m of acrylic and a metal frame and I bought it in the winter. When it was delivered there was a gap but now it has gone. On a hot day recently it was about 2mm too big. This is indoors and over a temperature range of about 10C. It seems a lot worse than the figure here: http://www.pmma.dk/Acryl_dimensionsstabilitet.aspx?Lang=en-GB.
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It is 19" wide so one of the first jobs I will do when I get my pro is stick it in the pass through slot and shave 2mm off the end.
BTW, my ultimate answer was @dwardio’s… re-scale the entire thing. Which is kinda what I figured I’d need to do. Got me close, but I think the original scale specified was actually off. My pieces had too much play in them to really work with. So I trashed it. And now I’m out of yellow transparent acrylic so I have to wait until I get more to try again.
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