When the printhead moves around while not printing which is also called "traveling" it may scratch the top of the print as the head is still at exactly the same height as when it printed that layer. It's not that nice to have on top of your prints and it can be hard to predict that it will happen. Fortunately, there are some very easy solutions to this problem.
Turn on Z-hop
Most slicers have a setting that is typically called "Z-hop" and allows the printer to move the printhead up slightly before starting the travel to the next section. The flip side of this is that print times can get longer because the printer has to stop completely and move the Z-axis up, move to the new location and run it down again each time it has to travel. In addition, it can also leave small blobs where it stops. Below is a list of where to find the option in different slicers.
- SimplyPrint slicer: Extra > Z-hop
- Cura: Custom > Travel > Z hop when retracted
- Simplify3D: Edit process settings > Extruder > Retraction vertical lift
- Prusa slicer: Printer settings > Simple mode > Retraction > Lift Z
Adjust the print factor for top layers
If your print factor or print multiplier is not perfect, plastic will often be pushed out to the sides and slightly up around the nozzle while printing. (The nozzle is the last piece of metal in which the plastic is melted and pressed out). When the printhead moves across this area again, the plastic will protrude a little higher than the nozzle is and therefore the hot nozzle will make its way through the plastic and leave scratches on the top. In your slicer, you will find a setting that controls how much plastic needs to be extruded (how much plastic the printer needs to push out of the nozzle) for a given section. If you turn that down a bit, you will be able to minimize the depth of the scratches. Below is a list of where to find the option in different slicers.
- SimplyPrint slicer: Outside > Shell print factor
- Cura: Custom > Material > Gear > Flow > Checkboks > Close > Material > Flow
- Simplify3D: Edit process settings > Extruder > Extrusion multiplier
- Prusa slicer: Print settings > Advanced mode > Filament settings > Extrusion multiplier