Mendel Prusa: Requesting advice regarding print quality

I have recently built a mendel prusa reprap. Finally worked through hot-end issues, and am now working on improving print quality.

Would appreciate any advice about printing improvement based on the following example part: The coupling for the stepper-motor to Z-axis threaded rod. This is the first printed part listed at [reprap.org]. The STL file is here: [github.com].

Pictures of the result are as follows:
TOP VIEW:


BOTTOM VIEW:


SIDE VIEW, showing uneven surface:


You will see that the top is not smooth. I have been trying to follow some of the calibration advice, particularly that found at [reprap.org] and at [richrap.blogspot.com]. I get pretty good results with the 0.5mm-thin-wall.stl recommended for calibrating the layer height and for the 20mm-box.stl calibrating infill. Although I do get a some "grabbing"/"tugging" which distorts the infill layers near the top of the 20mm box before it lays down the final layers.

Here is what I am using:
Sprinter firmware
Pronterface printer controller
Slic3r slicing software, with the following parameters
3mm PLA filament
.5 mm nozzle diameter
Temperature = 185

Layer height = 0.3 mm
Perimiters = 3
Fill Density = 25%
Retraction = 1.5 mm, 30mm/s
Infill speed = 80 mm/s
Lift Z = 0.2 mm

Looks like your e-steps/mm value is too high in firmware configuration.h.

remove the hotend and tell the extruder to extrude 100mm of filament. Measure how much it actually extruded with a caliper. You want this value to be as precise as possible. (I use +/- 0.02mm) Take the value it actually extruded, divide that by the number of steps/mm currently in your firmware and multiply the result by 100. That should give you a new value for steps/mm that you should put into your firmware. Repeat this process until it is as precise as you can possibly get it. 5-6 times if need be.

This should dramatically increase your print quality.

Also in Slic3r, make sure your extrusion multiplier is set to 1 for PLA.