July 12, 2013 - Update 2Thanks flurin. I had connected the z-extrusions facing the wrong side. After another failed attempt, I started suspecting the try square. It turns out the try square is not really "square". Yes, It can happen in India
. I bought a higher precision one and the offset is clearly seen in the old one.
Attempt 3: Granite slab serves as a perfectly level base.
The try square seems to be doing its job well.
I found it easier to align the coupler and the nut on the x-carriage by removing the threaded rod and resting the carriage on the coupler.
I will power it up and give it a shot tomorrow. Hoping for positive results.
July 2, 2013 - Update 1I ordered pre-assembled ORD Bot kit from RRD with RAMPS 1.4. Also bought QU-bd extruder.
Completed the mechanical assembly and wired the motors.
The Z-motor and flexible coupling for the threaded rod are totally off-center.
I re-built the frame again from scratch checking for alignment at every step.
I could only do minor corrections at the T-slot junction. The rod was still off-center. Finally, I decided to twist the z-motor mounts to align with the coupling.
X,Y motion is perfect. There are still some issues with the z-direction
.
1. If I align/fix coupling to the z-motor when the carriage is at z-min then I observe locking (only one z-motor rotates) at around mid section on the rod. If I align/fix the coupling when the carriage is at z-max then again there will locking near mid section. I used lube on the rods but it made matter worse so cleaned it back. I don't see any bent in the rods (at least with the naked eye ). I can see manually turning that at some points there is considerable force required but then it becomes easy later. Need to try with adjusting drive current to the motor.
2. The two vertical z-extrusions are not perfectly parallel. At Z-max only the outer wheels (with eccentric nut) turn and at Z-min only the inner wheels turn. The offset is about a mm or so. The carriage moves freely without the threaded rods connected. Not sure if this offset has any effect on the z lockup. I found it very difficult to align the z-extrusions.