Note: this is the standard (ft and inch) version. For the metric version click here
Step 11. Making the spiral staircase
The spiral staircase is a series of small wooden blocks (steps) fanned around a length of ¼" rod, and glued together.
Making the steps: From a length of 3/4" thick wood approximately 1¾" wide (more or less), cut 12 pieces (steps) at 2 3/8" long, and shape them as shown in the drawing below.
Drill a 1/4" hole through each piece, also shown in the drawing.
Thread a 1/4" thick x 20" long rod (the pole) through the holes in the steps. Have the pole sticking out 1/2" at the bottom. The part that sticks out goes into the hole in the bottom floor. Apply glue between each step and then fan them around to make a spiral of even treads. Then clamp them together until the glue dries.
Drill a 4½" diameter hole in the top floor where you want the stairwell to be, and a 1/4" hole in the bottom floor directly below to take the bottom end of the pole.
Next cut a piece of 3/4" x 1 1/2" (or similar) wood, 6" long (the pole support). Rebate the ends of the pole support as shown in the drawing below and drill a 1/4" hole in the middle of it.
The hole is to take the top end of the staircase pole.
Cut into the top of the internal walls so that the top of the pole support piece sits snugly in place,
and ensure the hole (in the pole support) is directly
above the pole hole in the bottom floor.
Note: There is no need to fix (glue or nail) the pole support permanently. You will need to remove it and replace it while fitting the staircase.