Most of the track on my O Scale model railroad is of the O27 variety. Whenever I need to separate a block of track, I need an insulated rail joiner. I also frequently buy used turnouts, preferably in large and well-trashed (but cheap!) junk lots, and they often are missing one or more of the necessary insulated rail joiners. However, since I happen to own few spare insulated rail joiners and am too cheap to buy some, I am left to using old pieces of electrical insulation and other junk in place of proper rail joiners--leading to considerable headaches. If only I owned a machine that could create anything I want out of plastic... Oh, wait.
Since I couldn't find any premade models for O27 insulating rail joiners, I made some minor modifications to this design (https://www.thingiverse.com/thing:7060520) and sent it to the printer! Well, actually, I sent it to Cura, then Octoprint and only then to the printer. It is a little finicky about bed leveling. Anyway, it should work with pretty much any piece of O27 track.