Experimenting with a support beam and a sliding insert, rendered these results. Could be adapted for many uses. Don't expect precision alignment as it is a loose fit, but will allow for use as a tracked slider. Good exercise for seeing how well your printer can print.
Mine produced prints that fit nicely without need for tweaking
. Added a lockable slide version with mounting holes. All holes are for 6-32 tap.
When tapping plastics, Use 91% Isopropyl alcohol as a tapping lubricant and break chips more frequently than you would for metal. You'll get very good threads despite how odd it may sound.

Added Slider 90 beam which is slotted to allow it to be glued to a slider at a 90 degree angle. 09/13/14