Why custom? By the time you design and build, and re-build, and design again, and re-build again, and break some stuff, and then buy stronger stuff, and then rebuild again, and end up with something that kinda works, you will have spent as much money and lots more time than it would take to just buy one of the many options available out there. Just sayin...
I think you might be looking for bronze or plastic bushings, also known as plane bearings. Check out McMaster.com.
Also, you need to define if you are working with pipe or tube. There is a difference, and there are many types. For example, nothing on 1-1/2 pipe is 1-1/2". I know, its weird but true. There is a reason, but it has to do with history.