Build a "working" tricorder

Step 4 Building the "head"

 The top, bottom, middle and sides of the tricorder are made of 1x4 pine (which is really 3/4 x 3.5 inches).  The sides of the head are just some scraps of 1/4 poplar.  My cardboard is about 1/4 inch which gives me the magic dimensions:  3.5 inches minus the two poplar sides, minus two cardboard sides = 3.5 - (2 x 1/4) - (2 x 1/4) = 3.5 - (1/2 + 1/2) = 2.5, which is the width of the iphone.  (Mine actually works out to 2 5/8, which matches the case for my phone).  

Cut a piece of pine of the same length as your cardboard box (maybe a hair longer) -- about 5 inches.  This is the top lid.  The top lid of the tricorder has a semi-circular profile.  I just traced an arc on the both sides, then used a drawknife to carve it out.  You could use saws, rasps or sanders.  Don't bother refining the shape too much -- you will complete the sanding in a couple steps.   The easiest way to do this is to screw a piece of scrap to the underside of the lid, and clamp the scrap in a vise, so you have unobstructed access to the top.

Next cut some sides out of the 1/4 poplar, about 3 inches high.  Drill and countersink two 3/4 brass screws on both sides -- the distance from the bottom of the side to the bottom of the lid is about 1.75 inches.   Trace the profile of the lid on each side.  Remove the sides, then cut out the profile just proud of the line.  Screw the sides back on, and sand the combined assembly so the lid and sides are smooth.  I labeled the sides and the lid with an "A" side and a "B" side since they are now precisely matched.