Build a "working" tricorder

Step 6 Hinge pins

 A "real" tricorder is hinged in the rear, but my model has a sliding hinge in the center.  Each side has a 1/4 dowel pin about 3/4 inch from the base, and a matching slot is cut in each side.  This design gives us a way to access the screws that hold the lid in place after the tricorder is assembled -- just slide the entire head all the way up.    Also, it's easier to build a symmetric head --  otherwise you need a long front edge and a short back edge for clearance.  The best thing to do is build some paper templates and experiment with hinge position, and make sure that you have sufficient clearance to rotate the head and unobstructed access to both sets of screws.

Drill a hole for the dowel pin, and press-fit 1 inch long sections of 1/4 dowel -- DON'T GLUE IT!  The dowel should be tight, but you should be able to remove it with your fingers.  It only needs to stick out about 1/4 inch from each side, but the extra length on the inside gives you something to grab so you can retract the pin and remove the head temporarily.  

Route or carve a 1/4 inch slot about 1/4 inch deep on each side from the base of the head to just shy of the peak.  Test each side with the hinge pin and make sure it slides smoothly.