Step 1: Materials and Tools
Small piece of PVC pipe. I think I used 2 inch diameter, about 3 inches worth, leftover from a plumbing project.
QTY 2 #8x3/4 flat head wood screws
QTY 1 #8x1 flat head wood screw
QTY 1 3/16 x 3/4 "binding post" or pin with retaining ring
Pattern - attached later
Scraps of wood
Tools that I used, suggestions as to what one could use will follow in the steps where the tools were used:
Stationary disc sander
11/64 drill bit
3/16 drill bit
13/64 drill bit
Countersink for #8 flat head screws
Step 2: Flatten the PVC pipe
Heat one piece at a time until it becomes soft and rubbery. Do this outside, I'm guessing it releases some fumes that you don't really want to breath. I used a heat gun (think a hair dryer on steriods), one could heat in boiling water or an oven. I'd avoid using an open flame, though placing it on a pan in a hot grill might work. Wikipedia says the melting point of PVC is between 100º and 260º C (212º-500ºF) I've tried the boiling water (100ºC) method and I don't think that is quite hot enough. Anyway, temp isn't important, soft and rubbery is. Experiment.
Once it is soft and rubbery, flatten out between two scraps of wood and clamp. High clamping pressure isn't really necessary, just enough to hold it flat. Allow it to cool. Repeat with the other half circle.