Yesterday I finished building the printer, so I printed my first object. A little 2cm cup.
While printing I saw something was wrong, the surface of the cup was wobbly and bumpiness. So I waited until it was done printing and measured the cup. The size on X and Y is okay, but the Z is 12 millimeters instead of 20 (see picture below).
For me it looks like it calculated the amount of PLA for a 20 millimeters cup (that’s why its so wobbly). So I think the printer is fine except for the Z axis which didn’t move down fast enough while printing.
When I control the printer by hand (using the computer or LCD on the printer itself) the Z axis moves just fine.
That looks pretty weird, and surely because it’s not all stringy, what temperature did you print this on? Was the front fan on? Because it looks like it just melted by having the head above it constantly, to prevent this try to print 2 cups at the same time and placing them with some distance appart on the printbed, that way every layer gets some time to cool down and settle.
Also in addition see if your z-axis moves freely. Move it with the manual controls in Repetier down 20mm and measure the distance. If it didn’t and was very loud, it might be binding up and the stepper might loose steps.
