Ok This first project is less about optics and more about solving a problem. Ever since I have had my telescope when I bought it at 15 on Craigslist, it has been missing the eyepiece holder on the focuser tube.
For the most part this wasn’t a problem as the focuser tube is very close to 1.25 inches and fits the eyepieces pretty snuggly. There is a little wobble which my impact image quality a bit and would just move the telescope to have the best image quality on the object of interest which was fine for me. The biggest risk was just the eyepiece falling out.
With the 3D Printer up and running I went about design a replacement. The final design can be found here on OnShape https://cad.onshape.com/documents/6c2b93c301d81fd13156a65c/w/dbd2b71c3528a5cccf87b7b3/e/df8993ec8ee1d7e4efd36834.
It is a simple design with threads at the bottom to match the focuser and 3 holes to take threaded inserts for thumbscrews. On cheaper models there is only one screw, which is probably fine give my use case but three is supposed to allow you to hold the eyepiece more evenly and was easy enough to do. The best eyepiece holders use a compression ring which is a thin piece of metal with a gap around inside the ring, and the screws press in to shrink ring and press more evenly and prevent marring of the eyepiece. Maybe if I have free time someday I will try to make one like that.
The toughest part of this build was getting the thread pitch and tolerance correct. For the pitch I used calipers to measure the pitch to be about 0.75 mm and guessed it was likely a round number so when with that which turned out to be correct. The thread is an equilateral triangle of 0.7mm and the inner diameter was tuned to be a diameter of 35.6 mm by doing some quick test prints adjusting until it screwed snuggly onto the focuser. The thickness was just eyeballed to seem sturdy.
The final result with the thread inserts already placed and some placeholder screws until I can buy some thumbscrews:
