【3D Printing】How to Successfully Print a Sphere
For 3D printing, spheres or spherical objects can be a challenge. Read on for some tips to improve the print quality of your 3D printed spheres!
Fused Deposition Modeling (FDM) 3D printers work by moving a nozzle along the X, Y, and Z axes, extruding filament at specific locations, and gradually creating parts layer by layer.
While FDM printing offers significant advantages in some respects, including ease of use for beginners, the layer-by-layer printing process also has its limitations.
A notable drawback of FDM 3D printers is that they produce "stair-stepping" on curves that intersect with the Z-axis.
Other aspects of the printing process can also limit print quality, such as Z-seams, inconsistent extrusion, and so on.
In particular, spheres are one of the most difficult geometries to 3D print, as they are more susceptible to stair-stepping.
If the print requires supports, there will be even more impact, as the smooth, curved surface of a sphere means that marks from support points will have nowhere to hide.
All the reasons mentioned above can lead to a rougher surface finish than usual.
FDM printed spheres will never be perfect, but there are several ways to minimize defects and achieve the cleanest possible surface finish.
In this article, we'll discuss some tips for 3D printing spheres using FDM.
Design
The first step to printing a sphere is to design it correctly, and there are actually two ways to achieve this: splitting it into two or keeping it as one piece.
Splitting a spherical shape into hemispheres will make printing easier and eliminate the need for supports, but it will increase post-processing time when you need to glue them back together, and you must be mindful of the possibility of warping where it contacts the heated bed.
If your spherical shape is part of a larger design, consider designing sections to be printed separately and reconnected later.
Alternatively, you can keep the spherical shape in the model but carefully consider its orientation when slicing.
Splitting a spherical object into two parts is straightforward.
First, open your favorite 3D design program and find the center point of the spherical object.
Then, use a split tool (plane or 2D sketch) to divide the model into two sections.
Finally, export each section individually to print separately.
It's best to print one hemisphere at a time to avoid retraction issues when the nozzle moves between each block.
If you keep the spherical shape as a solid, no special design preparation is needed.
Just export the model as usual, but be aware that you'll have to deal with the overhangs at the bottom of the sphere in the slicer. On that note, let's move on to slicer settings!
Slicing
Slicing your model is the next important step in printing a sphere, although adjusting slicer settings is critical for any successful print.
Better, smoother prints on the print bed mean less sanding and post-processing time.
To print a smoother-looking sphere, a very general but useful setting is to use a smaller layer height.
Simply put, higher resolution means less noticeable stair-stepping because more layers are used to create the curve.
While this will increase print time due to the extra layers needed to achieve the same height, the smoother surface achieved with such a simple setting adjustment will be worth it!
Features like Cura's adaptive layer height can also achieve finer details and faster print speeds; this setting is also available in other slicers, though the name may differ.
In short, this feature changes the layer height throughout the sliced model so that less detailed sections will print with thicker, faster layers, while highly detailed sections will print with thinner layers.
This is particularly useful for spheres, as it will create a smooth transition between layer heights, resulting in a natural, more rounded appearance while reducing stair-stepping.
A crucial part of printing a sphere is support. Theoretically, a perfect sphere would only touch the print bed at a single point.
However, 3D printers cannot print in mid-air, so the bottom of the sphere requires support structures to hold it during printing, otherwise, it will roll.
If you split your model in half, you can avoid this need, as each hemisphere can be printed on its flat base.
Often when support material is removed, the supports can leave marks or rough surfaces.
To minimize the impact on the sphere's surface, try increasing the distance between the support material and the overhang. (The relevant settings in Cura are "Support Z Distance" and "Support X/Y Distance".)
Using a raft or brim can also be a good idea to further provide bed adhesion for spherical parts.
Rafts and brims around the support structure and the area of the sphere that contacts the print bed help keep them grounded to the bed.
This is important because without a brim or raft, the support structure could fall off mid-print!
Infill and walls are the main body of the print, as they account for the internal fill and external surface, respectively.
The number of infill and walls is less critical for the surface appearance of a sphere, but should be set according to the part's intended use. For example, these settings can affect how light passes through an object, which can be helpful if you're printing something like a moon lamp.
For infill, a lower than usual infill density can be used unless the part requires strength from its internal structure. This will avoid any risk of the infill pattern bleeding into the walls. Lower infill density also means less print time.
If you want a degree of transparency, try using a smaller number of walls (around two).
That said, too few walls and too little infill can cause sagging where the infill gaps meet the walls.
To prevent this, consider using three or more walls when the infill density is around 10% or less. If you want a solid-looking surface and a stronger part, increase the number of walls.
For spheres, regardless of their purpose, always keep the wall count the same as the top and bottom layer counts. This is because if one number is greater than the other, the sphere will be unevenly weighted.
If your spherical part is not a plain sphere, you will also need to consider the part's orientation.
If you cannot split the part into two, the bottom half will require a lot of support, so keep in mind that removing supports can damage any fine details.
If your sphere is part of a larger model, try adjusting where you place the model to minimize the support required for the sphere itself.
Slicer settings often suggest using modes like vase or spiral. Vase mode prints only the perimeter of a spiraling object, which is great for cylinders and other hollow circular shapes. This will also reduce material consumption and print time. Just make sure not to forget to enable supports, otherwise, the print may fail.
Printing
There's not much to discuss when actually printing spherical objects, but before you start printing, check on the printer's regular maintenance.
This means making sure your belts, nozzle, heated bed, etc., are all functioning properly.
To ensure your spherical shape doesn't turn out egg-like, make sure to tighten the belts on both the X and Y axes.
Loose belts can cause the print head or print bed to move more loosely, so perfect circles can end up looking a bit oval.
Don't forget to ensure your nozzle is clear and clean, as a clogged nozzle can lead to inconsistent extrusion and a worse-looking surface quality.
As with any print, remember to level your heated bed before starting to print, so the first layer prints nicely and evenly.
Finally, consider printing spherical objects with materials like ABS.
While other materials like PLA should have similar printing success rates, ABS offers simple layer smoothing options, so the final result can be more impressive.
If you have a dual extrusion printer, try printing supports with a dissolvable material like PVA, as this avoids surface damage during support removal.
Post-Processing
Finally, to post-process the sphere, fortunately, there are many post-processing techniques depending on your print, material, equipment, and experience level.
For spheres, some good options include sanding, using solvents, polishing, and coating.
The first step you should take is to remove all support material from your print. Carefully use a tool to remove any last bits of support material adhering to the model.
If you printed your model in two halves, you might not need to remove supports, but rather bond the hemispheres together using an adhesive like super glue or a 3D pen.
When aligning the two halves for a seamless transition, aim for perfection as much as possible.
Next, sand the model with sandpaper from a low grit (coarser) to a high grit (finer).
If joining two hemispherical parts, ensure you smooth the transition between them and sand all areas of the sphere evenly for the best surface finish.
If you printed your model using ABS, you can use a solvent like acetone to give the model a smooth, shiny surface.
The solvent works by slightly melting the surface to blend the layers and remove visible lines.
If you printed your part using PLA, you can use an epoxy coating (such as XTC-3D) to smooth and finish your object.
Finally, you can polish, paint, or coat your model to give it the final touches.
Painting a sphere can hide any remaining imperfections on the object, add or emphasize details, or switch colors.
For a smooth shine, try using a rotary tool to polish at high speeds, or hand polishing works too.
That's how to print a spherical object that will look great anywhere!
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