Blobs and Zits


During your printing process, the nozzle moves at different portions on the print bed, and the extruder continuously retract and re-extrude. Every time the extruder turns on and off, it causes over extrusion and left some spots on the surface of the model.

∙ Extra Extrusion at Stops and Starts
∙ Stringing

Extrusion at Stops and Starts

Retraction and coasting settings

Observe the printer printing and check whether the problem occurs at the beginning of each layer or at the end.

If you notice that the spots always appear at the beginning of each layer, you may need to adjust the retraction setting. In Simplify 3D, click on “Edit Process Settings”- “Extruders”, under the retraction distance setting, turn on “Extra Restart Distance”. This setting can adjust the retraction distance when the extruder restarts to extrude. If the problem happens at the beginning of the outer layer, it may be caused by extra extrusion of the filament. In this case, set the “Extra Restart Distance” to negative value. For example, If the retraction distance is 1.0mm, set this setting to -0.2mm, then the extruder will turn off then re-extrude 0.8mm.

If the problem appears at the end of each layer printing, here is another function called “Coasting” in Simplify 3D can help. After enabling this setting, the extruder stops a short distance before each layer is completed to eliminate the pressure of the nozzle and reduce extra extrusion. Generally, set this value to 0.2-0.5mm can get an obvious effect.
Avoid unnecessary retractions

A simpler way than retraction and coasting is to avoid unnecessary retractions. Especially for the Bowden extruder, continuous and stable extrusion is very important. Due to the large distance between the extruder and the nozzle, this will make the retraction more difficult. In some slicing software, there has a setting called “Ooze control Behavior”, enable “Retract only when moving to an open space” can avoid unnecessary retraction. In Simplify3D, enable “Avoid intersection of movement path and outer walls” can change the movement path of the nozzle so that the nozzle can avoid the outer walls and reduce unnecessary retraction.
Non-stationary retractions

Some slicing software can set Non-Stationary retraction, which is especially helpful for Bowden extruder. Since the pressure in the nozzle is very high during printing, the nozzle will still extrude a little more filament after turning off. The steps for this setting in Simplify are as follows: Edit Process Settings-Extruders-Wipe Nozzle. The wiping distance can be set begin from 5mm. Then open the advance tab and enable the option “Retract during wiping movement”, so that the extruder can do Non-Stationary retractions.
Choose the location of your start points

If the above tips are unhelpful and the defects still exist, you can try to randomize the starting position of each layer in the slicing software, or select a specific position as the starting place. For example, when you want to print a statue, turn on the option “Select the place closest to a certain position as the starting point”, then enter the XY coordinates of the starting position you want as the starting point which you can choose on the back of the model. So, the front side of the print shows no spot.

Some blobs appear when the nozzle traveling. These spots are caused by a small amount of leakage of the nozzle at the beginning or the end of the movement.
Go to Stringing section for more details of troubleshooting this issue.

Date:2022-8-30 Author:admin