I wanted a hard case for my DM42 so that buttons wouldn't get hit when it was floating around in my laptop bag. There's another one on thingiverse but it looks a little bulky for what I'm looking for. I decided to make a simple case the calculator could slide in and out of.

I designed it to be just a little large so I could cut up the leather (?) pouch the calculator came with and glue it to the inside to add some snugness and protect the screen a little more. Works well for me, if you don't want to do that you can use some felt or modify my FreeCAD source file to make it so the plastic grips it more.