When considering retraction, keep in mind the potential tradeoff between unaesthetic and annoying strings (which typically can, however, be snipped/trimmed off after printing) vs. the potential for retracted filament to extrude as a “blob” at the start of new extrusion areas. Retraction is worth trying. But look at your print results with retraction to check that, in reducing strings between areas, you haven’t sacrificed “clean” starts of re-extrusion.
For objects without flat top surfaces, an alternative to retraction that may reduce stringing is to “Enable Combing” (under “PRINT SETTINGS”, “ADVANCED”, “Retraction”): this causes non-extrusion moves to attempt to stay within the perimeter of previously extruded material, so that any undesired “string” of excess extruded material simply ends up as additional infill. This won’t be that helpful if the object has multiple, separated contours at various layers (in which case many non-extrusion moves will have to traverse a void), and it tends to have the unfortunate side-effect of marring (with extruder head movement “comb” marks) any flat top surfaces. However, for objects without flat top surfaces and with (mostly) connected extrusion contours, “Enable Combing” may yield good results.
Also, check that the non-extrusion “Move Speed” (under “PRINT SETTINGS”, “ADVANCED”, “Speed”) is not unnecessarily slow; sometimes a faster “Move Speed” will reduce stringing.
If the issue is not the extruder “pulling” or “smearing” the edges, but rather that the edges are “curling up” as they cool, then sometimes faster cooling can aid in solidifying such edges before they have a chance to curl. For a printer with a “Cooling Fan”, enable it (under “PRINT SETTINGS”, “ADVANCED”, “Cool”); for a printer with an open print area such as a Polar3D printer, you may also point an external fan at the build platform.
Alternatively, for a filament such as ABS which is very prone to edge curl as it cools, reducing or eliminating cooling may improve the edges.
(Note that smeared, curled-up edges can even result in the extruder “catching” on a lip of previously extruded material and actually knocking the print loose of the build plate when the extruder comes to a section and resumes extruding; see item 4.)
If your 3D printer includes an object cooling fan, check that its use is enabled, and that it is running at proper speed; see the settings under “PRINT SETTINGS”, “ADVANCED”, “Cool”.
You may also see if “PRINT SETTINGS” for “Minimal Layer Time”, “Cooling Minimal Feedrate”, and “Cooling Head Lift” are helpful, as they are intended to, respectively, ensure that each layer takes a minimum amount of time, without slowing down the extrusion too much, and lift the hot extruder away from the object during the enforced delays between layers as the remaining “Minimal Layer Time” elapses. In other words, they are intended to help address this sort of issue. However, forcing the printer to idle (while the extruder remains hot) to keep from printing over a prior layer too quickly can cause its own sorts of problems with oozing melted filament, such as “stringing” from the edge of the object to the (now moved away) extruder, or “blobs” of melted, oozed filament getting deposited at the edge of the object when the extruder returns to resume printing, or under-extrusion if filament has oozed out of the melt chamber leaving it partially empty at the start of a new layer.
So using a combination of these mentioned settings may help, and sometimes be enough – but printing multiple objects simultaneously is often even more successful!
In particular, the Polar Cloud default is to only begin printing support when the object overhang angle (the angle between vertical and the object contour) reaches 60° – 3D printers can have remarkable success printing overhanging material. However, some objects will need support “sooner” (support even for less extreme overhangs); in such cases a “Support Angle” of 45° may be more appropriate (under “PRINT SETTINGS”, “ADVANCED”, “Support” “Support Type”, “Support Settings”).
A slightly lower-than-usual “Temperature” (under “PRINT SETTINGS”, “BASIC”) and faster cooling of the object layers may also help. If your printer has a cooling fan, check its settings under “PRINT SETTINGS”, “ADVANCED”, “Cool”; or if your printer has an open print area (as with the Polar3D printer), consider pointing an external fan at the print area during the print. Under “PRINT SETTINGS”, “BASIC”, a smaller “Layer Thickness” and a slower “Print Speed” may also allow the layers to cool more quickly (and hence droop less). (Alternatively, a thicker “Layer Thickness” sometimes “holds together” a little better – experiment to see what works best.)
In cases of not particularly wide bridge-span, and where only the upper (outer) surface of the bridge area will be important for the final object, it may suffice to use a slightly greater than usual “PRINT SETTINGS”, “ADVANCED”, “Quality”, “Top Layer Count”: even if the underneath side of a bridge area droops or has strings of filament dangling, an extra layer or two on the top may yield a “good enough” top surface appearance.
When feasible, printing an object in a different orientation (one that minimizes overhanging or protruding areas) can be very helpful; see Section 14.2.