Adventures in Optics Part 2

This part with the threaded end holds the lens and a 2" ID pipe slides into the non-threaded end.

The threaded end was 1.91" ID, so it would have partially obstructed the 2" diameter (actually 52mm) of the lens.  I was going to amputate the threaded version but then I found this threaded end cap:

I now have a cool dust cap that will never wear our or get easily lost.

I still have a few holes to drill here and there.  This ring goes inside the threaded fitting part to both center the lens in the tube and allow me to put setscrews in that fitting to press that ring for collimation adjustment.  

This started out as something else and needed to go from .5" to .25" wide.  Cutting on the mill would require tightening it down more in the mill vise than would be advisable for a weak, brittle material like PVC.  The lathe was the obvious choice.  Cutting that much off using the standard lathe tool is not practical. I do not have a parting tool for the lathe.  Perhaps I should get one.  

Solution: put it on the three jaw on that rotary table.  Bring 1/8" endmill to the outside of the ring.  Cut down into the ring very slowly.  Rotate the table at 50 inches per minute 

This is a cheap, likely only so-so strategy for collimation, but this is a finderscope, not a high end refractor so good enough 

This is how it will look after I get the lens in place.  The big ring on the left is a union to hold the main tube and eyepiece draw tube together.

One more thought.  The drawtube is now very thin wall.  1.31" OD and 1 25" ID.  I doubt that a thumbscrew would hold in such think material.  I will cut a 1.5" OD, 1 31" ID x .5" piece of carbon fiber to glue on the end of the drawtube, then tap a hole for the thumbscrew.   The black of that part will go nicely with the black of the helical focuser as contrast to the rest.

I am still waiting on 52mm ID O-rings.  In the meantime, flat black paint on interior and bright white on exterior. 

Paint.   I should have thought this through before pulling out the paint cans. Tape all holes on the inside before spraying interiors.   Then tape all holes on the exterior, paint exterior and interior. Then remove all tape on interior and paint again.  Then remove retake interior holes and paint exterior again.  Otherwise you get spray through the holes.  I will then touch the ends with a brush.