Mis-Aligned layers .. sometimes

I can not reconcile what is going on. If I print a plate with, lets say 8, small parts like an action figure, layers misalign. See pic

So what do you do? Print a 40mm tall calibration cube. And it comes out PERFECT! See pic

Mendel 90 MDF
Ramps 1.4
Printing from computer using Pronterface
Slic3r
Nophead Marlin optimized firmware

Belts tight. Extruder and steppers perfectly calibrated.

Any insights?

- Jim

Belt slipping.
Drive gear not tight on stepper shaft.
Binding on the axis that is shifting.
Stepper current not high enough.

No
No
No
Possible.

I have the problem (once in a while) and Im pretty sure the belt and the alu gear are tight enough (I even put used superglue to see if there is any cracking)


My skipping steps are always on the X axis and ALWAYS in one direction (It travels one step to the right further than it should)

Can it be that the filament drags the head , but if yes why is the problem, one step further to the right (it should be one step back).

it also seems that its always one step (but in some prints I have 2-3 steps missing in different layers)

Im puzzled really

(just upped the current a tad more for good measure)