pbackx

This could also be caused by the model itself and depends on the software you use to design the model. The create a circle, it is approximated by a number of lines: OpenSCad calls these lines "fragments" and you can specify how many fragments you want or how long you want the fragments to be. If you have too few fragments, you could get a similar result as what you show. So maybe check your design software and see if you can increase the resolution.

I seem to having the same issue. I see 'waves' or 'ripples' in my first layer. Similar to the last picture here: https://ultimaker.com/en/community/34262-pla-ripples If I manually turn the bed screws a bit (about a half or quarter turn) those waves disappear. So do I add the following to the start code to try to fix this?

Yes, I use the unload or change procedure in the user interface. I have this problem with both Ultimaker and other brand filament. I have only used PLA and PVA. The blob on a string happens with PLA. The only time I have used PVA, it was grinded when unloading and I needed to manually remove it. I do hear some things happening after the print is finished. I'll pay a little closer attention next time to see if the retractions are happening as you describe.

I have just got my Ultimaker 3 and so far I'm getting some great prints with no tweaking needed at all (an entirely different experience than my homebuild Prusa i3 clone) The only thing I don't know how to do properly is unloading or changing filament. Every time I unload or change filament, the old filament is quickly retracted from the Bowden tube, but that does not seem to work properly. Sometimes the filament is just stuck and the feeder grinds it. Most of the times however, it does retract, but a small bit of filament that (I presume) was in the hotend is also retracted. This little piece (a few mm) is only loosely connected to the rest of the filament and always gets lost somewhere in the feeder and I'm not able to remove it. I guess it's down there somewhere, preparing to wreak havoc in the future. So I'm wondering if I am doing this correctly. Should I first heat up the hotend before unloading/changing filament? Is there some other operation that needs to be performed before unloading? Am I not closing down the machine correctly?