Since I am assembling a number of OpenROV WTCs and their accompanying End Caps I thought that I would pass along how I built a couple of alignment tools to align the 10th, 11th, and 12th acrylic plates, with the 20 mm center holes, to the ~10 mm hole in the 9th acrylic plate.
I used a quality fly cutter equipped with a 1/4 in diameter drill to cut out a 20 mm disk in a 1/4 in thick piece of HDPE.
I used the fly cutter to cutout the 20 mm disk from both sides of the 1/4 in thick HDPE, but did not cut though enough on the other side to free the disk from the HDPE. I then took a quality ream and gradually opened up the fly cutter’s 1/4 in diameter drill hole until the cut down syringe slid into the hole without any slop. Finally I used a very thin, sharp Xacto blade to cut the disk out of the HDPE and sanded one side flush to the outer circumference.
I now have a quality alignment tool that will allow me to precisely center the 10th, and 11th, acrylic plates over the 10 mm hole in the 9th acrylic plate. I have made two alignment tools to align the slots in the 12th acrylic plate to the the 10th and 11th acrylic plates since the cut down syringe is not long enough to use the disk alignment tool for aligning the 12th acrylic plate.
Acrylic Plate #10 aligned by tool
Acrylic Plate #11 aligned by tool