In 3D printing, many users will encounter the problem of "wire drawing" or "hanging material", especially when printing complex structures or multi-segment models, the nozzle will leave filaments in the process of moving, which will affect the quality of finished products. In order to solve this problem, the Retraction function came into being, and one of the most critical parameters is the "retraction distance". This paper will analyze in detail the setting method of back pumping distance and its influence on printing quality.

# # What is back pumping?

Back-pumping refers to pulling the melted consumables back for a certain distance before the nozzle moves, so as to reduce the phenomenon of nozzle dripping or wire drawing on the non-printing path. Withdrawal includes two main parameters: one is withdrawal length, that is, the distance that consumables are pulled back; The second is the Retract Speed, that is, the speed at which consumables are pulled back.

# # Why do you want to set the pumping distance?

When the nozzle moves between two printing areas, if the melted consumables are still dripping, filaments or "cobwebs" will be formed on the surface of the model. This not only affects the appearance, but also may affect the structural accuracy of the model. By setting an appropriate pumping distance, these problems can be effectively reduced or even eliminated and the printing quality can be improved.

# # How to set a reasonable pumping distance?

1. The influence of material type

Different consumables have different fluidity, so different pumping distances are needed. For example:

-PLA material: generally, it is recommended to set the withdrawal distance between 1.0 and 6.0 mm (depending on the extruder type);
-ABS material: due to its high fluidity, the pumping distance is usually 6.0 ~ 8.0 mm;
-Flexible materials such as TPU: Due to its high elasticity, the withdrawal distance should be appropriately reduced to avoid material jamming, generally 1.0 ~ 4.0 mm;
-PETG material: due to easy wire drawing, it is recommended that the drawing distance is 6.0 ~ 9.0 mm.

2. The function of extruder type

-Direct Drive extruder: because it is close to the nozzle and has fast response, the withdrawal distance is usually short, and it is recommended to be 1.0 ~ 5.0 mm;
-Far-end (Bowden tube) extruder: Because consumables need to pass through a section of hose, the resistance is large and the pumping distance needs to be longer, and it is recommended to be 6.0~10.0mm；;

3. The influence of nozzle temperature

The higher the temperature, the stronger the fluidity of consumables and the easier it is to draw wires. At this time, the pumping distance should be appropriately increased to prevent dripping. On the contrary, when the temperature is low, the pumping distance can be appropriately reduced.

4. Influence of printing speed and moving path

If the nozzle moves fast, the back pumping can be reduced appropriately; However, when printing complex structures and frequent jumps, we should appropriately increase the pumping strength to avoid wire drawing.

# # Practical debugging suggestions

Although there are recommended values, the best pumping distance often needs to be determined through actual tests. You can print a special drawing test model (such as drawing tower), gradually adjust the drawing distance, observe the drawing situation and find the most suitable value.

# # Conclusion

Setting the pumping distance reasonably is one of the keys to improve the quality of 3D printing. It is not only related to the surface smoothness and detail expression of the model, but also affects the stability of the printing process and the use efficiency of consumables. Only by mastering the characteristics of different materials and equipment and fine-tuning through actual tests can the maximum efficiency of the pumping function be truly exerted. For every 3D printing enthusiast or professional, understanding and optimizing the pumping distance is an important step towards high-quality printing results.