Your 3D printer must execute a lot of changes in extruding in movement directions during the printing process. If the settings of retraction are not optimized, it could lead to defects on the surface of your print. Sometimes these deformations are also called zits or pimples.
Retraction is the pulling backwards of your filament during the printing process. When the hotend of your 3D printer is moving to a new location (extruder moves without extruding) strings may occur, because the melted filament is oozing out of the nozzle. This can be improved by pulling back the filament in the moment your hotend stops extruding.
First, make sure that you have enabled retraction.
Second step will be to optimize retraction settings, like retraction – distance and speed.
The distance defines how much the filament is pulled back of the nozzle. It depends on your printer what the best distance will be. Try it out by printing two cubes which are 40mm away from each other and increase retraction distance by 0,5mm and monitor the best performance. For most printers, the retraction distance should be between 1 and 5mm.
The retraction speed is also an important setting that influences your print. If you retract the filament too fast, the filament may separate from the melted part. Otherwise, if you retract too slow, the nozzle may leak before starts printing at the new position. For most printers, the retraction speed should be between 20-100 mm/s or 1200-6000 mm/min.
Try it out by printing two cubes which are 40mm away from each other and increase retraction speed by 20mm/s or 1200mm/min steps and monitor the best performance.
Sometimes blobs occur if your nozzle has filament residues on it. New printed filament can catch the residues and may cause defects in your print.
Common defects are little blobs at the start / layer tab point of your print. To eliminate these completely can be very difficult. An easy solution/work around is to select new start point, which attract not so much attention. Your slicer software only wants to optimize the process, they are not intelligent and cannot realize the back or front of your print, therefore you have to choose the start point.