Lithophane Light Box Frame

This is my first attempt at designing a lighted frame box for displaying 3D-printed lithophanes. It has three 50x80mm openings and one 164x80mm opening. Lithophanes to fit should be printed at 53x83mm and 167x83mm, all 1.5mm thick. The lithophanes mount in an insert which fits inside the front of the case; a front panel snaps on to hold the lithophanes in place. It's easy to swap out lithophanes by flexing the front panel slightly and removing it. EDIT 2/4/18 - I've been experimenting with different thicknesses of lithophane ... 1.5mm is a little thin, and results in more visible artifacts because you don't have all that many 'shades of grey'. I've been getting better results with slightly thicker lithophanes - 2 or 2.5mm. You just need to make sure the outer 1.5mm of each lithophane is not too thick, so that they fit beneath the front frame. I've been getting good results by printing at 2.5mm, with a 60% gray border (1.5mm wide) in the original photo so that the outer edge of the final lithophane is less than 2mm thick.