Piano Hinge, expandable, lays or hangs flat ver2 (corrected)

Print two halves, slide a 3mm rod in and presto - you have a hinge.

Mix and match lengths to get the desired size.  It's helpful to print in pairs, less confusing that way.

Use double sided tape to attach to surface, VHB tape works well (I think VHB means very high bond, 3M has some and you can find generic VHB).  I don't know if VHB sticks to PLA, let us know in the comments.  VHB works well with ABS.

Optional: Insert a M4 x 4mm machine screw into each end and the hinge pin (that's the 3mm rod) will stay in it's hole.

BOM:

• 3mm rod, LOH - 10mm: any metal will work.  I use cheap stainless steel.  I.E. a 60mm hinge will need a 50mm rod.  → LOH = length of hinge.  Tip: A clean end will slide in easier than an end with burrs.
• 2 M4 x 4mm screw, any head works fine, IMHO a button head is more aesthetically pleasing.

Settings?  That's pretty much up to you and how strong the hinge needs to be.  A good start point would be:

• Layer: 0.20
• Width: 0.40 
• Walls: 3
• Top & Bottom: 4 

Tip:  Is the rod is too tight? Drill out the holes.  But you say: “I don't have a 3mm drill bit long enough.”  Here's the fix:  Make a D-bit: Get a length of rod and file or grind about 10mm or so flat to the center of the rod.  Try to make the edges you are making sharp, those will be the cutting edges.  The end of the rod will look like a 'D'.  Chuck your new D-bit in a drill and drill that hole out.  Oh, go slow to not heat up the plastic and empty the shavings out often.