I Am Continuing Building the Low Power, High Brightness Finder Even Without My Mill Working

All the parts are circular.   With enough forethought you can make anything circular on a lathe.

I came up with an unnecessarily complex lens cell design.  Two halves that would contain the lens with 2-56 screws holding the halves together.  I realized part way through that I could just bore a 1" thick piece of Delrin 0.8" deep 2.1" ID bore and the lens will just slide in.  Then I need to machine a 2 1" OD,  2.0" ID, 0.25" thick ring that goes inside the entry side of the cell and use a couple 6-32 screws to secure this retaining ring inside the cell.

Boring a 2" hole inside a 2.25" piece of Delrin on the lathe is easy.  I first trying using a 2" Forstner bit but the drag was so much that the drill chuck kept turning in the tailstock.   Solution: start with a small Forstner bit and work my way up to 2".

I still need to turn the outside diameter of the cell to 60mm so it slides loosely into a 62mm ID PVC tube.  Even though a lathe should center a drill hole pretty precisely, it is clear that the hole is not quite concentric and the cell is a bit more thsn 60mm OD.  The stock I started from is 2.559" OD.  Once the cell slides into the PVC tube, i have three set screws in the tube to collimate the lens cell in the tube.