Delrin is Too Flexible

While Delrin has lovely tensile strength and machines really nicely its Young's modulus is about 1/20th of aluminum.   My attempts to trim the exterior diameter of that lens cell will not work.  Holding it tight enough to turn on the lathe stretches it enough that, I think, it works loose from the jaws of the chuck and goes flying.  When I tried to trim it by putting it on a chuck on the rotating table, i had a similar problem even with very light cutting depths and speeds.

I think the solution is either use aluminum tubing as quickly as quickly starting point or CFC. Starting from aluminum tube should turn okay.  I will trim exterior first, then interior 

Round CFC tube this size seems scarce.  Another strategy, which might work with Delrin is to start with a 1" thick piece of Delrin in the mill, and cut the ID first and then the OD.  The exterior structure means no need to hold it in a chuck.

I ordered a foot of 2.5" OD 2.0" ID aluminum tube.  I can cut an inch and turn down the OD to 60mm and bore a 52mm hole .8" deep for the lens.