This is from the early days of using our 3D printer. We've since acquired more printers and gotten a lot more complicated.
The top is held on by screws threaded into nuts. The nuts are slipped into a fitted slot in the side of the bosses in the base.
I engraved the acrylic panel in front of the controller box on my milling machine. Overkill but when all you have is a hammer everything looks like a thumb.
this one isn't showing the picture???
inside the box
Here's a closer look at putting a nut in a slot. Instead of 3D printing, the slot could be made on a mill. This is to hold a temperature probe for the above controller