The stringing, is the mistake that makes the prints “hairy”. It’s due to the unwelcome leakage of plastic from the nozzle. This molten plastic, resembling a spider web, normally occurs in the movement spaces of the nozzle. Where there are no printing parts to support it.
You have to fix this problem as soon as possible. Besides being aesthetically unpleasant, it can compromise (even if in a minimal way) the integrity of our print! In fact, the material that forms the filament is completely removed from the print, and in some special cases, for example, if the object to be printed has large gaps between the walls can also undermine the structural integrity.
Stringing: Here’s what to do
A series of measures can reduce if not eliminate this problem. The first one is to use supports if the space between 2 points of a print is too large.
The media leaves no gap under the print and essentially simulates the printing of an object without sudden changes. As mentioned before, just avoiding the passage of the nozzle through wide open spaces contributes could reduce the stringing of 80%.
Simplify3D in this case meets us because it has an option called “Avoid crossing outline for travel movement”. Cura with the third version has also implemented a similar function. This does not allow the extruder to make real “jumps in the dark”. Keeping it above the model even when moving.
However, we realize that it is not always possible to avoid connections or use supports. So, here is some adjustments that can lead to the elimination of the problem.
The first parameter to which we will have to pay attention is just the temperature. In fact, it is responsible for the dissolution of the filament, if it is too high the plastic will melt and will leak into the nozzle even when the remaining filament will be correctly retracted.
The first adjustment to be made is to decrease the temperature by 5 degrees in 5 degrees, and analyze if and how much the situation improves from time to time. This in the vast majority of cases almost completely solves the problems, if the settings are correct.
Stringing: Increase travel speed
Raising the speed leaves less time for the plastic to run off, it is an unorthodox but functional remedy.
The overwhelming majority of printers are able to tolerate 150 mm/s speed well, and we may already notice some differences.
Stringing: Let’s get the retraction right.
If, after all these tricks, we still find “spider’s web”, we will have to start working on the retraction.
First of all, we can start by dispelling a rather common myth about retraction. People say, retraction sucks the filament from the nozzle. This mistaken belief may lead us to think that the more retraction is used, the less tightening will occur.
Actually once the filament has melted in the hot-end it cannot be withdrawn, the only way it could be withdrawn would be by having a vacuum extruder, where a retraction of the filament would correspond to a decrease in pressure and therefore a suction effect, but we know that this is not the case.
The only effect that the retraction exerts on the extruder is to decrease the thrust (even if only gravitational) and not to force the filament to descend.
Recommended values of retraction
Normally, retraction values between 3-4 mm for direct extruders, 6-7 mm for bowden and a retraction speed of 35 mm/s ensure smooth printing, but some special conditions or materials require different settings.
PETG will often give this problem and it will be difficult to solve it, so prepare patiently and ad hoc shears to remove the filaments!
Unfortunately, in this case the only solution is to proceed by trial and error by gradually increasing 1 of these values at a time and observe the improvements.
Surely retraction values of more than 5 mm for the direct and 10 mm for the bowden extruders do not bring further benefits. The increase in retraction speed above a certain threshold, 45 mm/s, on the other hand, can create serious problems, already described in this article which describes the phenomenon of abrasion of the filament by the extruder.
Some filaments seem to have a specific value for the quantity and speed of retraction. So if you are lucky enough to find the optimal values, don’t forget to write them down on the reel!