In 3D printing, spheres and spherical objects can sometimes be difficult shapes to produce. Here are some tips for achieving a cleaner finish when 3D printing spheres!
FDM (Fused Deposition Modeling) 3D printers build objects by moving a nozzle along the X, Y, and Z axes, extruding filament at specific locations and stacking layers little by little.
While FDM printing has many advantages, such as being beginner-friendly, the process of layer-based manufacturing comes with several limitations.
One of the major drawbacks of FDM 3D printers is the occurrence of "stair-stepping" on curved surfaces that intersect with the Z-axis.
There are also factors that limit print quality, such as Z-seams and uneven extrusion.
Spheres, in particular, are one of the most difficult shapes to 3D print. Because they have many curved surfaces, they are highly susceptible to the effects of layer-induced stair-stepping.
Furthermore, if support material is required for the build, it becomes even more challenging because support marks are left on the sphere’s smooth curved surface.
These factors can result in a surface finish that is rougher than usual.
While it is difficult to achieve a perfectly smooth finish on an FDM-printed sphere, there are several methods to minimize defects and obtain the cleanest surface possible.
In this article, we will introduce several points to keep in mind when printing spheres with an FDM 3D printer.
Design
The first step in printing a sphere is to design it properly. In practice, there are two ways to do this: splitting the sphere into two pieces or keeping it as one part.
Splitting a sphere into two hemispheres makes the build much easier because it can be printed without support material. However, note that you will need to glue the two parts together later, which increases post-processing time, and be aware of the possibility of warping at the contact surface with the print bed.
If the spherical shape is part of a larger design, consider designing the parts so they can be printed separately and connected later.
Alternatively, you can leave the spherical shape as is within the model and carefully consider its orientation during slicing.
Splitting a spherical object into two is very simple.
First, open your preferred 3D design software and find the center point of the spherical object.
Next, use a split tool (a plane or a 2D sketch) to divide the model into two.
Finally, export and print each part separately. To avoid retraction issues when the nozzle moves between parts, it is recommended to print the hemispheres one at a time.
If you keep the spherical shape as a single solid, no special design preparation is required.
Export the model as usual, but remember that you will need to address the overhang at the bottom of the sphere in the slicer. Now, let’s look at the slicer settings!
Slicing
Slicing the model is the next critical step for printing a sphere. Adjusting your slicer settings is a key point for a successful print.
If you can achieve a smoother finish on the print bed, you can reduce the time spent on sanding and post-processing.
One very common and effective setting for printing smoother spheres is to decrease the layer height.
Simply put, higher resolution creates curved surfaces with more layers, making the stair-stepping caused by stacking layers less noticeable.
Although print time will increase because more layers are required to build the same height, the smooth surface gained from this simple setting change is well worth it!
You can also balance finer detail with faster print speeds by using features like "Adaptive Layers" in Cura. This setting is also included in other slicers, though it may have a different name.
Essentially, this feature varies the layer height throughout the sliced model, using thicker, faster layers for parts with less detail and thinner layers for parts with more detail.
This is particularly effective for spheres. By smoothly changing the layer height, you can reduce stair-stepping while achieving a more natural, rounded appearance.
Support material is important when printing spheres. Theoretically, a perfect sphere only touches the print platform at a single point.
However, since a 3D printer cannot print in mid-air, a support structure is needed to hold the bottom of the sphere. Otherwise, the sphere will roll around.
If you split the model in half, you can avoid this issue, as each hemisphere can be printed from a flat bottom surface.
Usually, removing support material can leave marks or cause a rough surface.
To minimize the impact on the sphere's surface, try increasing the distance between the support material and the overhang (In Cura, these are the "Support Z Distance" and "Support X/Y Distance" settings).
Using a raft or brim is also a good method. It can further increase the adhesion of the spherical part to the bed.
By placing a raft or brim around the support structure and the area of the sphere in contact with the print bed, you can securely anchor the object to the bed.
This is a critical point. Without a brim or raft, the support structure might collapse during the print!
Infill and walls are the main parts of the print, forming the internal structure and external surface, respectively.
The number of infills and walls is not as critical for the look of a sphere's surface, but they should be set according to the part's intended use. For example, these settings can affect how light passes through an object, which is useful when printing things like moon lamps.
Regarding infill, you can usually use a lower infill density unless the part requires internal structural strength. This reduces the risk of the infill pattern showing through the walls. Lowering infill density also reduces print time.
If you want to achieve a certain degree of transparency, try reducing the number of walls (to about 2 layers).
However, if there are too few walls and infill, sagging may occur where the infill gaps intersect with the walls.
To prevent this, consider using 3 or more wall layers if the infill density is around 10% or less. If you want a solid surface and a stronger part, increase the number of walls.
For a sphere, regardless of its use, always keep the number of wall layers equal to the number of top and bottom layers. This is because if one value is larger than the other, the weight balance of the sphere may become uneven.
If the spherical part is not a perfect sphere, you should also consider the orientation of the part.
If the part cannot be split into two, the bottom half will require a large amount of support material. Remember that this may damage fine details when removing the supports.
If the sphere is part of a larger model, adjust the placement of the model to reduce the support material needed for the sphere itself as much as possible.
It is also recommended to use similar modes such as Vase Mode or Spiralize mode in your slicer settings. Vase mode prints the outer perimeter of a hollow object in a spiral, making it suitable for cylinders and other hollow, circular shapes. This also reduces material usage and print time. However, don't forget to enable supports if necessary, or the print may fail.
Printing
There is not much else to explain when actually printing a spherical object, but before starting, ensure your printer is well-maintained.
Check that belts, the nozzle, and the print bed are functioning normally.
To ensure the spherical shape doesn't turn into an egg shape, make sure the X and Y-axis belts are properly tensioned.
If the belts are loose, there will be play in the movement of the print head or print bed, which can cause a perfect circle to look slightly oval.
Also, make sure the nozzle is clean and free of clogs. A clogged nozzle can lead to uneven extrusion, which can worsen surface quality.
As with any print, level the print bed before starting to ensure the first layer is printed cleanly and evenly.
Finally, consider printing the spherical object with materials like ABS.
While other materials like PLA are considered to have a similar success rate, ABS has easier methods for layer smoothing, which may result in a more beautiful finish.
If you are using a 3D printer with dual extruders, try printing the support material with water-soluble materials like PVA. This will allow you to avoid damaging the surface when removing the support material.
Post-Processing
Finally, post-process the sphere. Fortunately, there are various post-processing methods depending on the print, material, equipment, and experience level.
For spheres, sanding, solvent treatment, polishing, and coating are all good options.
The first thing to do is remove all support material from the printed model. Carefully use tools like a craft knife to remove even the last fragments of support attached to the model.
If you printed the model in two parts, you might not need to remove any support material. Instead, you can join the hemispheres using adhesive agents like superglue or a 3D pen.
Align them as accurately as possible to ensure the two hemispheres connect evenly.
Next, sand the model using sandpaper, moving from coarse to fine grit.
If you glued two hemisphere parts together, smooth out the seam and sand the entire sphere evenly to aim for the cleanest possible surface finish.
If you printed the model in ABS, you can use a solvent like acetone to achieve a smooth, glossy finish.
The solvent slightly dissolves the surface, allowing the layers to blend and removing noticeable layer lines.
For parts printed in PLA, you can use an epoxy coating like XTC-3D to smooth out the surface of the model.
Finally, you can sand, paint, or coat the model to finish it.
Painting the sphere can hide fine defects remaining on the surface, add or highlight details, or change the color.
For a smooth, glossy finish, try using a rotary tool at high speed to buff in polishing compound. You can also sand by hand.
These are the ways to print spherical objects that look beautiful from any angle!
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