10 July 2020 updated most parts to fix some geometry glitches and improve strength.
Another update, corrected the lettering size on the top case.
Added a vertically oriented top case as per my suggestion below, I think this one would produce best print quality and also requires no support if printed with Cura's adaptive layers. I'm printing one using .2mm layer 100% infill.
Update! (yes already)
I spotted an error with the top case, it was missing two board mouning pillars. Now fixed!
BTW the case in the picture is an actual ZX81 that I used to make the model here.
The ZX81 was my first computer, many hours were spent playing games like 3d Monster Maze and others, and typing in games from magazines then losing it all due to ram pack wobble, but it still holds a place in my heart that I just can't let die.
I'm currently repairing a few old computers and needed a case for an orphan ZX81 board (pictured) that I was given a few years ago.
However I could not find a replacement case, so I modelled one from scratch over the weekend.
I also need a new ULA but I might get one of the new vla81's when they start making them again.
Please don't expect this to be an exact copy of the ZX81 case, it's very close but might differ in some measurements, although I've taken care to make sure the critical dimensions are correct.
That said, if anone has the correct measurement for the keyboard membrane recess in the top case I would be happy to correct the model. Although I have one working ZX81, I don't want to peel off the original membrane to find out.
For best print quality, I think the bottom should be printed as supplied, but the top may look better if printed vertically with the back on the build plate. supports should not be needed if printed in this orientation,
However you will need good bed adhesion.
If you are printing the case top on a machine with a moving y-axis, orient the model so the model is aligned in the y-axis not x-axis as the y-axis movements may cause wobble as the printing nears the top.
Cura has an option to select face to orient with build plate, so it should be easy to set up.
The screw holes in the bottom have been made to fit the feet that I have included.
I welcome any constructive comments to refine this model if any adjustments need to be made.