Newbie Prusa i3 printing issue (Slic3r)

Hi,

I've build a prusa i3 using the bundle offered by Sintron on Amazon (http://www.amazon.de/gp/product/B010LHPXUS?psc=1&redirect=true&ref_=oh_aui_search_detailpage) .

After a lot of calibrating issues, I've now managed to configure Marlin so that the axxes move the correct distances and the amout of extruded PLA matches the length defined in pronterface.

By the way, especially the value used for E-axxis was hard to find, since it differs significantly from the Default value. So for the MK8 Extruder, I've found the following.
#define DEFAULT_AXIS_STEPS_PER_UNIT {80.0429,80.1881,4000,96.3975}

Now I've downloaded the 25mm_cube.slt file and sliced it with sli3r.
After changing the Layer height to 0.2mm and the Filament Settings to 1.75 mm and 190 degrees (for all layers), I was able to print the bottom layer quite nice. But when it began to print the walls, too much filament has been extruded.

The nozzle was hopping over the uneven surface and finally, the y-axxis moved ~3cm and the printing continued next to the object.

I'm using natural PLA with a recommende temperature of 190 - 220° Celsius.

What can I do to change this?

Thanks and best regards,
Thomas

Have you defined the extrusion width for all in Slic3r or left the default to "0"?
Leaving the defaults can cause all sorts of extrusion problems.

If my nozzle is 0.4mm would 0.4mm be the correct value for the Extrusion width?

Thanks,
Thomas

In theory yes, in reality you want a bit more to ensure proper bonding and flat lines.
A good guide is to be 1.2 times higher than the nozzle diameter.
So for a 0.4 nozzle that would be 0.48mm - 0.5 might be better if you want to work with even number for the wall of your objects.
Always easier to squeeze 4 0.5mm lines into a 2mm wall than doing it with gap fill
But that is only cosmetic.

The extrusion width will ensure good bonding between layers. But it seems you are over-extruding. For a quick check, reduce the extrusion multiplier by 10-20% and see the effect. If it gets better, go back to #define DEFAULT_AXIS_STEPS_PER_UNIT and enter the right value for your E-axis.

To calculate the right value use:
E_steps_per_mm = (motor_steps_per_revolution * driver_microstepping) * (no_of_big_gear_teeth / no_of_small_gear_teeth) / (hobbed_bolt_effective_diameter * pi)
you need to measure the diameter of yout hobbed bolt at the hobbed bit where the filament enters.

If you have a direct drive system, you will not have the gear ratio and instead of a hobbed bolt you'll have a hobbed/toothed insert or similar.