Sight Tube and Cheshire eyepiece for collimating newtonian reflecting telescope

thingiverse

Sight tube and Cheshire eyepiece are two essential tools for collimating a reflecting telescope. A mis-collimated scope will produce blurry images. There are numerous online resources explaining how to collimate a scope using these tools, such as the one found at http://www.astronomyhints.com/collimation.html. There are two versions available: the classic Cheshire eyepiece and sight tube as separate tools, or a combined sight tube Cheshire. If you prefer having only one tool, use the combined version. However, if you find the cross-hair of the sight tube distracting when using the Cheshire part, opt for the separate tools. To print the separate tools: Print the sight tube in black filament using the STL file "sight_tube.stl." Ensure the outside cylinder is smooth by printing it with the cylinder vertical. No supports are required. Then, pull nylon monofilament thread across the notches and glue down to form a cross-hair. Gorilla glue works well for this purpose. Print the Cheshire body in matt black filament using the STL file "cheshire_body.stl." It's essential that the outside of the cylinder is smooth. Supports are necessary to support the oval opening on the side. Print cheshire_plug.stl in white plastic and insert it down the hole of cheshire_body.stl. Align the plug so the diagonal surface is lined up with the oval hole in cheshire_body.stl. To print the combined tool: Print cheshire_plug.stl as described above. Then, print combined_body.stl in black plastic using the STL file "combined_body.stl." Use supports and print the cylinder vertical. Push the cheshire_plug down into the cylinder of the combined_body and align the sloped surface to the hole in the side of the combined_body. Finally, pull nylon monofilament thread across the notches in the other end of the body and glue to make a cross-hair. It's not necessary to glue the plug into the body; friction holds it well enough. However, the cross-hair made from the nylon thread is quite delicate, so consider covering it with an end cap for 1.25-inch tubing. These tools have been printed in ABS and work just as well as commercial versions made from aluminum. It's worth noting that I haven't tried printing them in PLA.