Re: Idea for unused 3.5" bay
Nobody makes them, so you'll probably need to adapt what's available. For something that size, I'd say a push/push type latching system would be the way to go. I think they sell them at IKEA separately. Drawer runners can be simply a strip of plastic that runs in a groove. I wouldn't bother with an end stop to keep the drawer from coming out all the way. It'd be cool to stealth the whole thing in behind an original drive bay cover too.
Re: Idea for unused 3.5" bay
Stealting it behind a drive cover is the plan ;) As for the latches, we don't have an IKEA here, but I think something like this would work best: http://www.ebay.com/itm/push-to-open...item2ecef465e3 Don't want to use the magnetic ones that close to my HDD. Not sure what is available for runners, I guess I'm going to have to go to the local hardware stores and see what they have.
Re: Idea for unused 3.5" bay
Magnets next to hard drives are not a problem. The falloff distance for a magnet is exponential. And sitting it on the hard drive case wouldn't do anything to it with a magnet of the size you'd use for this. Now, a 6" neodymium block might be cause for worry.
Not sure what type of tools you have, but a simple runner could be made by cutting a rabbet on a table saw into the edges of some pieces of acrylic. One narrower piece to attach to the box, rabbet both edges to form a rail, rabbets facing toward the box. Two more pieces with a single rabbet each would attach to the case, with the rabbets facing the case, opposite direction of the other ones. They'll key together and form a slide. (If that confuses you more than it confuses me, I can make a sketch.)
Re: Idea for unused 3.5" bay
Good to know about the magnets. Unfortunately, I don't really have any tools aside from a dremmel and hand tools. I think I know what you are talking about, like a sliding tongue and groove kinda?
Re: Idea for unused 3.5" bay
Yep. Thinnest way to do it, rather than using an actual drawer guide. You could also make them from some stacked sheet stock.
Re: Idea for unused 3.5" bay
lol this thread made me think of this. (if any of yall remember it from way back when)