3D Printing Wall Thickness: How to Set It Perfectly?
In traditional manufacturing processes, parts are either solid or hollow, with no distinction between the internal and external areas of the model. In contrast, for 3D printed parts, the internal and external areas are technically separate, because the way the machine prints these two regions is completely different.
The interior of a 3D printed part is filled with infill, while the exterior is referred to as the shell. The infill can be printed at any density between 0% (hollow) and 100% (solid), and can also be printed in various specific structures. The shell, on the other hand, is completely solid.
The shell is not only the most prominent element in 3D printing but also has a significant impact on the mechanical properties of the model, such as strength. It consists of the walls, top layers, and bottom layers of the printed part. The former makes up the vertical outer region, spanning the height of the print, while the top and bottom layers cover the horizontal areas.
These two regions are different because the walls cover the horizontal perimeter of the print and extend upward along the Z-axis. The top and bottom layers cover the entire horizontal area within the perimeter established by the walls.
The shell and its subcomponents are essential elements of any 3D print, as mentioned, they affect the strength and durability of the part. Therefore, it is crucial to ensure that the shell settings in the slicer align with the intended use of the 3D printed part.
In this guide, Unionfab (one of the top 3D provider service in Asia) will discuss the most important shell settings, including the wall, top layer, and bottom layer settings.
1:Main Setting
Almost all 3D slicing programs that convert 3D models into 3D printable G-code have shell settings. However, before we begin, we should note that most of the terms used in this article are based on Cura. However, the terminology used in other 3D slicers should be fairly intuitive. For example, in Slic3r and PrusaSlicer, the shell is referred to as the 'Perimeter.
These settings can determine the quality of the print, because if they are not set correctly, your object will surely have visual flaws. Many different settings can affect the way the shell is printed in one way or another, but there are a few super important settings to focus on.
1. Thickness, Line Count, and Layer Count
For wall thickness, top layers, and bottom layers, the most important setting is probably the thickness of the shell feature. Unfortunately, in most cases, no slicer allows you to directly set the shell thickness because it is usually divided into wall thickness and top/bottom layer thickness.
Additionally, the shell thickness setting is typically represented by the number of lines or by width/height (in millimeters). These two shell thickness settings are directly related, so adjusting one will automatically adjust the other. Therefore, you can adjust them according to your preference.
In Cura, the wall width in millimeters is called 'Wall Thickness,' and it determines the width of the printed walls. In the other method, the wall line count setting represents how many times the nozzle will pass when printing the wall.
The settings for top and bottom layer thickness are very similar. Top and bottom thickness refers to the height of the layers. You can choose to adjust them in one setting or adjust them separately.
The top and bottom layer settings define the line count. But keep in mind, if you use this method, the actual height of these layers will depend on the overall layer height setting for the print.
The shell thickness or line count value should be adjusted based on the model’s intended use and the printing material, as there is no one-size-fits-all approach. The more walls you have, the longer the print time and the more material the machine will consume. At the same time, your part may also be stronger.
2:Suggestions
Now that you understand all the shell thickness settings, it’s time to set the wall thickness (or line count) and top/bottom thickness (or layer count) in the slicer. Common values for printing regular, medium-strength parts include: wall thickness of 0.8–1.6 mm (3-4 wall lines), and top/bottom thickness of about 0.8–1.2 mm (4-6 layers, depending on the layer height setting). In most cases, the slicer’s default values are suitable.
However, if you want to customize the values, you might need to know some rules of thumb:
Special Applications
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There are also some special methods for using shell thickness, such as using zero top and zero bottom layers to display the infill pattern. For example, this is common in jewelry or phone cases.
Another example is using a thicker shell without infill in functional parts that involve frames or rod-like structures. For instance, in this phone stand model, all the horizontal dimensions are very small, so a thicker shell can replace the infill.
Depending on the part's design, the shell can provide greater part strength than an equivalent amount of infill material. It may also increase flexibility.
2. Other Settings
Now that you understand the ins and outs of shell thickness, it’s also helpful to know about some other important settings. With these settings, you can fine-tune the shell of your model to prevent visual and mechanical defects.
Infill Overlap Percentage.
This setting typically controls the amount of overlap between the infill lines and the shell, affecting the bonding between the two and the overall strength of the print. Would you like more details on how this setting works?
This setting refers to the overlap between the infill lines and the walls. The value entered is a percentage of the infill line width. The higher the value, the tighter the bond between the walls and the inner print.
In Cura, the default value for this setting is 30%. You can increase this value by 10% to improve the strength of the model. Conversely, you can reduce it by 10% to save material and speed up the printing time.
Print Speed
Print speed refers to how quickly the 3D printer moves the print head while printing, and it can impact both the quality and the strength of the final print. Would you like more information on how to adjust it or its effects?
Another important consideration is print speed, especially for the inner walls, outer walls, top layers, and bottom layers. These settings determine the print speed of the elements described in the print, and they also affect the print quality of the bottom layers. It is important to note that the inner walls refer to the walls adjacent to the infill (the innermost walls), while the outer walls refer to the visible outermost walls.
The default value in Cura is 30 mm/s, which includes the wall speed as well as the top and bottom layer speed. We recommend increasing the inner wall speed to 30–60 mm/s because no one will see the inner walls, and setting the outer wall speed to 20–45 mm/s. For the top and bottom layer speeds, we recommend keeping them the same or reducing them to around 20–25 mm/s, so the top and bottom surfaces will look more aesthetically pleasing.
We use such a wide range of speeds to account for differences in material standard speeds (for example, the print speed for ABS should be slightly slower than for PLA). However, you can also freely adjust the speed to 30 mm/s based on the intended use of the model.
Layer Height.
Layer height settings also help adjust the shell, primarily the top and bottom layer components. The layer height controls how much higher each consecutive layer is compared to the previous one, and since the top and bottom layers are actual layers, they depend on this setting.
Essentially, the higher the layer height value, the stronger the part will be, but with fewer details. The default layer height in most slicers is 0.2 mm, and we recommend keeping the layer height at this value. However, if your model has more intricate details, you may need to reduce the layer height; if you need a stronger part, you may need to increase the layer height.
More Settings
Besides the slicer settings we’ve discussed above, there are some other tools that can affect the print quality of the walls. Below, we list some useful slicer settings and slicing modes that allow you to further adjust the way the walls are printed, beyond the basic settings:
1. Print Thin Walls: Sometimes, the model will contain features that are smaller than the wall line width, and the slicer will ignore them. This is because, technically, these thin walls cannot be printed as they are not wide enough to form a full wall—unless you use a smaller nozzle diameter and a lower wall line width value. This feature allows your slicer to recognize thin walls and assign a wall line to create a slightly over-extruded wall.
2. Wall Flow: Wall flow is similar to the overall extrusion flow rate, sometimes referred to as the extrusion multiplier, but it applies only to the walls of the model. You can use this setting to prevent over-extrusion or under-extrusion, and also to control the bonding between walls. This is because higher flow values will cause more material to be squeezed together in the same space.
3. Vase Mode: Vase mode, sometimes referred to as spiral mode, is a special printing mode that turns the model into a vase, using only a single wall for the entire exterior. Vase mode also allows the slicer to print the model with smoother and more natural Z-axis movements, thereby eliminating the common visible Z-seam.
4. Blur Skin: Finally, Blur Skin is a rare but interesting 3D slicer setting, which is somewhat related to wall thickness. When 'Blur Texture' is enabled, the printer slightly shakes the nozzle while printing the outer wall. This creates a blurry texture on the outer surface. If your slicer has this setting (Cura does), it’s a cool and unique feature to use.