I've been trying to build a belt and pinion carriage as shown in the example build video ( http://openbuilds.com/builds/v-slot-belt-pinion-example-build.97/ ), but I'm having problems getting enough pre-load of the wheels against the rails. Even with the eccentric spacers turned all the way in, the carriage is still loose against the rail. I've attached some pictures and video showing my build. Perhaps I'm missing something? I also took some measurements with calipers and noticed my 60mm rail measures only 59.75 (+-~.05). Is my rail out of spec? (I measured the hole center-to-center distance on the carriage plate as 80.68mm, which seems to match the drawings.) Has anyone else experienced this issue? Any ideas about what might be wrong or suggested solutions would be appreciated.