Tips to Prevent 3D Print Stringing & Blobs

3D printing stringing and blobs are quite common issues and can be caused by various factors especially print settings rather than the printer itself. Now let's start from what 3D printing stringing and blobs are, and then get into the useful tips to prevent 3D printing stringing and blobs from happening.

What is 3D Printing Stringing or Oozing?

3D printing stringing is also known as oozing, hairy prints. When filament strings appear between two different locations or hairy filaments appear on the surface of the print, it means 3D printing stringing happens. It's typically caused by filament oozing out from the nozzle while the extruder moves to the next location of the print. That's why we also call it 3D printing oozing.

3D printing stringing often happens at open space between two locations.

Tips to Prevent 3D Print Stringing

It's quite common that the melted filament keeps coming out of the nozzle due to inertia and gravity while extruder moves to the new section of the model. To fight against this issue, slicers like Cura, Simplify 3D offer a setting named as retraction, which pulls back filament while the extruder moves to next location.

Enabling retraction and change retraction settings in a slicer is always the first option to prevent stringing in our daily 3D printing projects.

1. Increase Retraction Distance

Retraction distance decides how much the filament will be retracted from the nozzle.

For direct drive extruder, the value is recommended within 0.5-2.0mm.
For Bowden extruder, the value can be as high as 15mm due to the long distance between the extruder drive gear and the nozzle.

Advice: when stringing happens, increase the retraction distance by 1mm to see if stringing reduces.

Retraction settings in Cura

2. Increase Retraction Speed

Retraction speed determines how fast the filament will be retracted. Too low retraction speed certainly results in stringing.

Advice: It's better to set retraction speed within 20-100mm/s, and slowly increase the value can help you solve the stringing issue.

3. Decrease printing temperature

Too high printing temperature also leads to 3D printing stringing. Too much heat inside the hotend makes the filament less viscous and stringing happens.

Advice: decrease printing temperature by 5 - 10℃ per time to find out appropriate setting for your printing task.

Recommended printing temperature for different materials:

PLA: 180 - 220 ℃

ABS: 200 - 250 ℃

PETG: 215 - 235 ℃

TPU: 235 - 250 ℃

4. Increase Printing Speed

Too low printing speed means the nozzle will move slowly between two locations and stringing can happen.

Advice: Increase printing speed by 10mm/s per time when needed to further solve stringing issue.

Recommended printing speed: 150 - 200mm/s

5. Clean the nozzle

When print for a long time with a same type of filament, for example, PETG filament.
The filament will form a thin layer inside the nozzle. This will lead to stringing as filament strands stick to the surface of the print.

In this circumstance, it's better to clean the nozzle and make sure no filament residue is inside.

6. Replace with new filament

Opened filament will gather moisture during use. If the spool has too much moisture, it will lead to stringing.

Try replacing it with a new and unopened filament spool

7. Apply thermal Paste

If the nozzle is encountering a heat dissipation issue. It's better to apply some thermal paste onto the threads between the heatbreak and the heatsink. This will help heat dissipation and reduce possible stringing.

8. Enable "Avoid Crossing Outline for Travel Movement"

"Avoid crossing outline for travel movement" is a setting in Simplify 3D. It can be enabled to minimize the length of the travel path for the extruder. This means the extruder has a travel path more above the print than crossing the open space.

So, If you're facing stringing issue, you can try this option in Simplify 3D.

What are 3D Printing Blobs and Zits?

3D printing blobs and zits are symptoms as blow image shows.
There are irregular bumps, ridges, or abnormal filament accumulation over the surface of 3D printing models. 3D printing blobs and zits do not only affect the appearance of the model but also lead to issue of functional prints.

Tips to Prevent 3D Print Blobs and Zits

Before we proceed, it's better to make sure the printer is well leveled, has right E-steps value and Z-offset setting, and its nozzle is correctly installed. These factors will confuse us with 3D printing blobs and zits issue.

After excluding above factors, now let's proceed to below approaches to prevent 3D printing blobs and zits.

1. Tune for correct extrusion

Calibrate the extruder for appropriate extrusion is quite crucial to prevent blobs.

Guidance:
https://all3dp.com/2/extruder-calibration-6-easy-steps-2/

2. Lower Printing Temperature & Speed

Too high printing temperature leads to over extrusion and too high printing speed means less time for the filament to settle.

Lower printing temperature by 5 -10℃ and printing speed by 5-10mm/s per time to find out the best setting.

3. Adjust retraction setting

3-1, set appropriate minimum retraction travel value to avoid too frequent retractions

3-2, increase the value of retraction distance to avoid blobs.

3-3, Increase retraction speed by 25% to get appropriate setting.

4. Increase Cooling Efficiency 

Too hot nozzle causes over extrusion and keeps the filament at melted condition too long.

Check if the blower fan which cools the nozzle works properly; if not, replace it with a new or more powerful one.

Increase fan speed by 10% per time to enhance nozzle cooling until blob issue won't happen again.