I made this center drill jig using an Ultimaker 2, PLA filament, Tinkercad, and Cura. The center jig shown has a 3/4 inch hole. Using Tinkercad you can easily manipulate the design to fit different sizes. You can even convert it to millimeters if you need to.
After a suggestion to make the guide 1/8" I redesigned and printed a new one. The new version can be printed using the center-revision .stl file I have included.
Step 1: Step 1: Import the Included .stl File Into Tinkercad If You Want to Change the Design, If Not Skip to Step 2.
If you have never used Tinkercad there are numerous tutorials on how to use it online. Their new user tutorials are great. After importing the file into Tinkercad you can manipulate the design to fit your application.
Step 2: Step 2: Import .stl File Into Cura
Cura is a free slicing software for your 3D printer. Make sure that after importing the .stl file you change the settings to match your printer and needs. You can see from my photo that I used just a light infill. So far it has proven to be sturdy enough. Once you have the design ready you will need to save it as gcode. For the ultimaker 2 you save the gcode and .stl file to an sd card and it it then ready to print.
Step 3: Step 3: Drill Away
As you can see from the photos it works great on both square and round tubes/pipes. Once picture shows it on a counter top. If you need to drill a hole into the center facing of the counter it would be very easy with this. I plan on making numerous more in various sizes. I just wish I had one of these years ago when trying to drill straight holes through pipe.