This is my first "thing", designed with freecad to house a printrboard and be bolted onto the frame of a m90 or similar reprap.
Printrboard should be quite snug inside (about 2mm clearance on each side and around 5mm at the top), and big hole is for all the connections (including power). The two smaller holes on the side are for usb/sd access.
The screws intended to mount the board are those that you would find on a standard computer (typically used for holding the case closed or for mounting 3.5" hdd's). The screws intended for holding the lid down are M4 self-tappers. The screws for holding the 40mm fan onto the lid are M3's (the fan i use was designed with those in mind and even has a hole for the m3 nuts).
The Nuts in the picture are the nuts im using with my board, from left to right, M3x15 (fan), Self-tapper of im-not-sure size (holds the lid down), 6-32'd used with computers (for holding the board into the box).
If you do print it, i'd love some feedback either here or on #reprap on irc.freenode.net (im shihan).
Updated design for new lid mount holes (should print easier).
The original cad design has now moved off to my github printer design (https://github.com/takigama/pjrun)
Update: Flipped the lid over in the STL (also its repaired with netfabb now cause the stl freecad generates is slightly invalid - the version on here has always been this way, this is just an fyi if your generating it from freecad directly)
Update: Printrboard mount holes were about 0.25mm out in each corner (fixed). Screw holes were all too small for intended screws (fixed).
Update: Shifted USB/SD holes, Resized USB hole for different types of usb cables. Im considering whether I should change the wire exit hole and move it more to the left (close to the corner).
Update: added images of box with lid. Quite happy with how well the lid and box comes together, they fit very well and the fan holes are spot on.
Update: Added an image of the box actually on my printer (lots of things held on with blue tape and double sided tape as they are temporary lodgings)