Stringing is the annoying occurrence of fine strands of plastic left behind in places where there should be nothing. Here is an example of bad stringing:
Fortunately it is possible to specify slicing program parameters that result in almost negligible stringing. Here is a photo of a string test part I printed recently:
Notice the extremely fine hair-like strings between the points. This is about as close to truly stringless printing I have been able to achieve so far. I was able to remove these hairs in just a few seconds by simply running my fingers between and around the points:
You can download this string test part here.
What causes stringing?
The answer is simple: pressure and viscosity.
3D printers emit melted filament from the hotend nozzle because of pressure created inside the nozzle’s melt zone. This pressure is caused by the printer’s extruder mechanism pushing more filament into the melt zone than it can hold. As a result, melted filament is forced out of the nozzle to accommodate the incoming filament.
When the extruder stops extruding filament the pressure in the melt zone does not immediately drop to zero. This is especially true for delta style printers (like mine) or any printer that uses a Bowden tube. The net result of this is that, because the melt zone pressure goes to zero over a short period of time, some filament will still be extruded even after the extruder has stopped feeding filament.
Viscosity is the characteristic of any fluid to try to hold itself together. Melted filament is a fluid with fairly high viscosity, so it tends to stay in a continuous stream (or string). Consequently, when the nozzle stops emitting filament and moves away from the position if had when it stopped, there will almost certainly be a thin string of filament left behind.
Parameters to minimize stringing
All slicers have parameters that you can use to minimize stringing. These are the ones I have found to be most effective:
In general it helps to print at the lowest possible temperature. This makes the melted filament more stiff and less prone to make strings. For PLA I use a temperature of 185C.
Note that this is not a good temperature for good printbed adhesion, so for the first layer I use a temperature of 215C. Depending on the slicer I use this temperature for either just the first layer, or the the first few layers.
I haven’t used other types of filament, so I can’t say anything about what temperatures to use for other than PLA, but in general I’d recommend the lowest one possible.
For any printer that uses Bowden tubes I recommend setting both Prime & Retract to 7.00 mm to start with. Somewhat different values might be needed by different types printers. Direct-drive printers can usually use much smaller values – perhaps aslittle as 0.5oo – 2.00 mm. Again, trial and error is the best way to determine the optimum value.
Note that in any case both Prime and Retract values should be the same.
I use 80 mm/sec which seems to work well. I’m not sure how much of an impact on stringing this value has. I’d appreciate any feedback on this (or any of my other settings) anyone might have.
Last Update: 13 May 2017