These parts are designed to be used with 1/2 inch Schedule 40 PVC pipe
Created with TinkerCad, these parts use PVC pipe, without the constraints of commercially available plumbing connectors.
The "sleeve" pieces allow a lot of adjustment, so precisely cut lengths of pipe are usually not required; slide the piece until it fits the connector.
The holes are set up for 1/4-20 machine screws (1.5 inch) and #6 sheet metal screws (half inch).
The "end pieces" and "flange pieces" can be printed without supports.
Test prints are advised as the manufacturing tolerances of PVC pipe are unknown to me. I used PLA (.35mm nozzle, .2mm layer height, 2 perimeters).
WARNING; The strength of these pieces has not been determined. Good layer adhesion is critical. Obviously, prints made with nylon (or other high performance filament) will be much stronger than PLA or ABS. Also, the design of your project is critical; PVC pipe isn't terribly rigid. A connector every 12 inches or so should suffice for most projects but test them first. Print a few connectors, assemble them, and see how much force it takes to break them. That should give you an idea of how suitable these parts are for your project. No warranty is expressed or implied, but have fun.
UPDATE 13-Apr-2014: There was a layer flaw in the "endpieces" and the file has been replaced with a corrected version.