@fastfreight
Cut the 1-1/2" PVC coupling. (You’ll make three cuts.) (One coupling makes two cups.)
First I cut the length of the coupling to 1-1/8". (Use a piece of 1-1/2" PVC pipe to hold the coupling against the fence of the miter saw. (Around 18" to 24" PVC pipe) Don’t cock the coupling against the fence. You want a nice square cut.
Next cut the coupling in half. (Again use the piece of 1-1/2" PVC pipe to hold the coupling.
My Miter Saw has a 12" blade. To Cut the coupling in half you will need to do a practice setup first. I lowered the blade toward the bed to see approximately where the center of the blade would contact the center of the 1-1/8" length of the coupling. The end of the coupling toward the fence was out about 3-1/2" from the fence. A piece of 2" x 4" wood stud laying flat on the bed against the fence worked just fine... I already had a short piece of a 2" x 4" to use. You only need about an 8" to 10" piece. (The width of your fence block depends on the diameter of your Miter Saw Blade).
Next find center of the coupling. Mark the center on both sides of the coupling using a lead pencil. Also mark the factory end of the coupling so you can see the center. You will use this when turning the coupling to cut the other side of the coupling, making two halves.
(Make sure the end of the 1-1/2" PVC pipe is a good square cut. Verify by making a fresh square cut.)
Slide the coupling over the piece of 1-1/2" PVC pipe. Flush up the outer edge, (the cut off edge), of the coupling to the front of the PVC pipe.
This next part I did free hand. You could probably clamp the pipe to the saw bed. I felt comfortable doing it free hand. YMMV... Hands are not near the blade. That’s what the 18" to 24" piece of 1-1/2" PVC pipe is for.
Next:
Firmly push the PVC pipe/coupling against the 2" x 4" wood block. (Your wood block). Make sure you have the PVC at a right angle against the wood block. Lower saw blade. Align the center of blade on the pencil mark you made on the coupling.
* * *(Warning, the wood block is a must! Looking at the blade toward the motor the blade rotates clockwise. The bottom of the blade rotates toward the fence. Without the block when the spinning blade contacts the coupling it would be forced back towards the fence.)
Start saw.
Lower blade, slowly making the cut through one side of the coupling. Note, you will also be cutting a slot through the 1-1/2" piece of PVC pipe holding the coupling as well. Continue lowing the blade slowly until the blade cuts through the coupling wall. Lowering the blade too fast you might splinter the back side, inter wall of the coupling.
Next:
Something I didn’t do but would the next time. Before cutting the other side of the coupling first put a piece of tape evenly spaced down the middle of the cut you just made. This will hold the coupling together, (minus the saw cut), when cutting the other side. I didn’t tape the side I had cut first and just turned the PVC pipe/coupling 180 degrees. I aligned the blade to the center mark on the coupling and made the cut. When the blade cut through the coupling the two pieces went their separate ways. I picked the two pieces up off the floor. No big deal but the tape would of held, kept, the two cut pieces together.
Next:
I took a piece of 120 grit sand paper, sanded off any burr edges. Then slightly rounded the two 1-1/8" sharp cut tails of the cup. Don’t sand, round off, the back edge. The back edge will glue to the duplex plate. You want a tight looking fit against the plate.
