Help fellow 3d printerist. My printrbot simple metal was fine and now it starts outputting these strange over-extrusion for the bottom layer.
What could be the cause of this? I have measured my filament and it consistent with the value 1.75mm that I put into cura. My print speed is only 30 and the bottom layer is only printed at 20mm pee second.
I have the same problem, the rest of the print is fine. I turned down my temp from 200 to 190 and it seems to have gotten better.
I will give that a try. Thanks.
I had a similar problem, and found I had my z offset too low. It was restricting the flow out of the nozzle and clumping up. Try moving the z offset up about .10
If it’s only on the bottom layer, increase your probe offset.
It turns out to be a probe offset issue. Specifically the bolt holding the ubis hot end loosen and the hot end moves downward a few 1/10 of a mm. This makes the first layer single lines look flatten. And the restricted flow causes the issue. Thank you all 
Everything is running smoothly now. One more thing to learn to diagnose.
Little loctite should prevent that happening again after recalibrating
@Jim_Wilson Might consider using the “light” loctite though (I think it is blue or HF#22) that is made to be forced off if necessary instead of the stuff that is basically all but permanent glue.
Lowering temperature may help.
loctite HGG. (hot glue gun)
