I always wanted a professional camera dolly to capture tracking shots, but couldn't rationalize spending the $$$ that most of the camera stores charge. So, I decided to print my own.
The rails utilize some steel rods from a storage unit I'm no longer using. The only purchased parts were the mini-bearings and a cheap camera quick release attachment.
You'll need to modify the basic design to fit your particular rails and/or camera mount.
Other than that, it's print, assemble, and use. The rollers include small plugs on the bottom for ease of printing. THe plugs pop out easily.
Here's a short video covering the dolly design and usage process. There is also a short demonstration at the end of the video showing how well it works for tracking dolly shots:
The next step will be to add small cavities and o-rings to the rollers to reduce any noise created by the plastic rolling directly on the rails.