【3D Printing】How to Successfully Print a Sphere
For 3D printing, spheres or spherical objects can be a challenge. Read on for some tips on improving the print quality of 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 to gradually build a part layer by layer.
While FDM printing is very advantageous in some aspects, including its operability for beginners, the layer-by-layer printing process also has its limitations.
One significant disadvantage of FDM 3D printers is that they produce "stair-stepping" on curves that intersect the Z-axis.
Other aspects of the printing process can also limit print quality, such as Z-seams, inconsistent extrusion, etc.
In particular, spheres are one of the most difficult geometries to 3D print because 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 there's nowhere for support marks 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 surface finish possible.
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 do this: split it into two or keep it as one whole.
Splitting a spherical shape into hemispheres will make printing much easier and eliminate the need for supports, though it will add post-processing time when you need to re-glue them together, and you must be aware of the possibility of warping on the contact surface with the heated bed.
If your spherical shape is part of a larger design, consider designing the parts to be printed separately and reattached later.
Alternatively, you can keep the spherical shape in the model but carefully consider the orientation when slicing.
Splitting a spherical object into two parts is very straightforward.
First, open your favorite 3D design program and find the center point of the spherical object.
Then, use a splitting tool (a plane or a 2D sketch) to divide the model into two parts.
Finally, export each part individually for separate printing.
It's best to print one hemisphere at a time to avoid retraction issues as the nozzle moves between each section.
If you keep the spherical shape as a solid, no special design preparation is needed.
Simply export the model as usual, but be aware that you'll have to deal with the overhang at the bottom of the sphere in your slicer. With that in mind, let's move on to slicer settings!
Slicing
Slicing your model is the next important step for printing a sphere, although adjusting slicer settings is key to any successful print.
A better, smoother print on the print bed means 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, as 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 through 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 areas will print with thicker, faster layers, while detail-rich areas will print with thinner layers.
This is particularly useful for spheres, as it will smooth transitions between layer heights, resulting in a natural, rounder appearance while reducing stair-stepping.
A crucial part of printing a sphere is support, as 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 would roll.
If you split your model in half, this need can be avoided, as each hemisphere can be printed on its flat base.
Typically, when support material is removed, it can leave marks or a rough surface.
To minimize the impact on the sphere's surface, try increasing the distance between the support material and the overhang. (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 contacting the print bed help keep them grounded to the bed.
This is important because without a brim or raft, the support structure might fall over in the middle of printing!
Infill and walls are the main body of a print, as they account for the internal fill and external surface, respectively.
The amount of infill and walls is less critical for the surface appearance of a sphere but should be set according to the part's purpose. 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 infill density than usual can be used unless the part requires the strength of an 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 certain degree of transparency, try using a smaller number of walls (around two).
That said, too few shells and too little infill can lead to sagging where infill voids intersect the shell.
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 layer count the same as the top and bottom layer counts. This is because if one number is greater than the other, the sphere's weight will be unevenly distributed.
If your spherical part is not a plain sphere, you 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 the placement of the model to minimize the support required for the sphere itself.
Slicer settings recommend using patterns like vase or spiral mode, which only prints the perimeter of spiral objects, making it ideal for cylinders and other hollow circular shapes. This will also reduce material consumption and print time. Make sure not to forget to enable supports, otherwise, the print may fail.
Printing
There's not much to discuss when it comes to actually printing spherical objects, but before you start printing, check your printer's regular maintenance.
This means ensuring your belts, nozzle, hot bed, etc., are all functioning correctly.
To ensure your spherical shape doesn't end up looking like an egg, be sure to tighten the belts on the X and Y axes.
Loose belts can cause the print head or print bed to move more loosely, making perfect circles appear somewhat oval.
Don't forget to ensure your nozzle is clear and clean, as a clogged nozzle can lead to inconsistent extrusion and make the surface quality appear worse.
As with any print, remember to level the hot bed before starting the print so that the first layer prints beautifully and evenly.
Finally, consider printing spherical objects with materials like ABS.
While other materials like PLA should have similar print success rates, ABS offers simple layer smoothing options, so the final result can be even more impressive.
If you have a dual extrusion printer, try printing support materials with soluble materials 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 the print. Carefully use a tool to remove the last bits of support clinging to the model.
If you printed your model in two halves, support removal might not be necessary. Instead, use an adhesive like super glue or a 3D pen to bond the hemispheres together.
When aligning the two halves for a smooth transition, be as perfect as possible.
Next, sand the model with sandpaper, from low grit (coarser) to high grit (finer).
If joining two hemispherical parts, make sure to smooth the transition between them and sand all areas of the sphere evenly for the best surface finish.
If you printed your model with ABS, you can use solvents like acetone to give the model a smooth, shiny surface.
Solvents work by slightly melting the surface to blend the layers and remove visible lines.
If you printed the part with 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 for a final touch.
Painting a sphere can hide any remaining imperfections on the object, add or emphasize details, or change colors.
For a smooth shine, try using a rotary tool to polish at high speed, or hand polishing works too.
That's how to print a spherical object that looks great anywhere!
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