While you may think that printing a simple object such as a sphere should be straightforward with a 3D printer, a sphere is one of the hardest things to get right in the world of 3D printing.
In fact, the correct methodology for 3D printing a perfect sphere is one of the most asked things in the 3D printing world, especially by 3D printing beginners.
So, what can you do to print a perfect sphere with your 3D printer?
A simple twist you can use to 3D print the perfect sphere is to print both halves of the sphere separately and then glue the halves together. The limitations that make it hard to produce a full sphere are avoided by printing hemispheres due to the geometrical differences between these two shapes.
As you can see, the complex problem of 3D printing a sphere can easily be solved with a bit of outside-the-box thinking. While this solution could feel like magic to you, it’s nothing more than understanding the limitations behind 3D printing and how the shape of a sphere falls into these limitations.
Now, let’s get into detail about what these limitations are and how they actually make it hard to 3D print a sphere.
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Why Is It Hard to 3D Print a Sphere?
A sphere is a shape that we commonly encounter in our daily life in objects such as basketballs and marbles. In fact, despite not being a perfect sphere, our very Earth is a spherical object.
Compared to all the complex models you can print with a 3D printer, a sphere is merely a simple shape without any nuances.
So, why is 3D printing a proper sphere is considered to be one of the most challenging things to do?
Simply put, the answer is gravity. If you take a closer look at a spherical object, you will realize that certain points of it don’t have any support below them.
The difference becomes very apparent when you compare a spherical object to a cubic one, as a cubic object doesn’t have any parts that are sticking out.
But how does this tie in to 3D printing a sphere being hard?
If you ever watched your 3D printer as it’s printing, you might have noticed that it prints in layers where the printer moves from the bottom of the shape to the top. Each completed layer acts as a support for the next one, allowing the layer to stay on the object without succumbing to gravity.
Now, think about the shape of a sphere again. Until you reach the very center of the sphere, each 3D printed layer is larger than the previous one, meaning that these layers aren’t supported by anything. When layers aren’t supported, there is a chance that they succumb to gravity and fall depending on the angle formed between themselves and the previous layer.
This phenomenon, called an overhang, is what makes 3D printing a sphere hard, and 3D spheres aren’t the only case where you will be experiencing this exact problem.
What Are Overhangs, Bridges, and Supports?
In the 3D printing world, parts of objects that extend beyond the previous layer are called overhangs, and trying to 3D print a sphere is perhaps the first time a 3D printing beginner encounters this concept.
Due to not having any support below them, overhangs are incredibly susceptible to falling as gravity can eventually pull them down during the printing process.
For more understandable examples, we can look at the shapes of the letters T and Y. The left and right pieces of these letters are overhangs, with the letter T having a 90-degree overhang and the letter Y having a 45-degree overhang.
As the angle of the overhang increases, so does the likelihood of it falling, as it becomes harder for the overhang to find support.
While slightly different than overhangs we have talked about so far, bridges are also a type of overhang. The most common example for a bridge is the letter H, as the middle part of this letter doesn’t have any direct support below it despite being connected to two separate points. Compared to overhangs, bridges pose less of a risk to the integrity of your print.
Since overhangs are the enemy of a successful 3D printing process, it’s best to eliminate or at least minimize them as much as possible by manipulating the model in certain ways.
An example of this would be to print the letter Y in a way that it lies flat on the 3D printer instead of printing it upright. With this simple modification, your model would contain no overhangs at all.
That being said, it’s not always possible to manipulate your model in a way where it wouldn’t contain any overhangs, which is where supports step in.
Supports are extra 3D printed parts that are added to your model as a way of supporting overhangs. As their whole purpose is to prevent overhangs from falling, they are removed from the print after the printing process is over.
If we use the example of the letter Y once again, adding two sets of supports to the left and right sides of the letter would allow the overhangs to stay in their place during the printing process.
While supports are a necessary tool in complex models, problems related to overhangs in simpler models can often be remedied by simple modifications such as the orientation example we have just mentioned.
How Does Printing Hemispheres Solve the Overhang Problem?
Now, let’s talk a bit about how splitting a sphere into two hemispheres solves the overhang problem.
Opposed to a sphere where the area of the layers increases as you go up until you reach the middle, a hemisphere can always be oriented in a way where the bottom layers are larger than the ones that follow them.
Because of this, a hemisphere will have sufficient support in each layer, and so, no overhangs.
Technically speaking, you could cause a hemisphere to also have overhangs by changing its orientation, which shows us how manipulating the orientation of a model can make a huge difference in how healthy your print will turn out, and how you can use model manipulation in your favor.
Next time you’re presented with overhangs in your model, make sure to remember this simple strategy and see if you can apply something similar to avoid having to use supports.
While it may not be apparent to a 3D printing beginner, what makes it hard to 3D print a sphere is simply the existence of overhangs.
Even though supports are considered to be the primary way of dealing with overhangs, easier solutions are available in certain cases. For instance, splitting a sphere into two hemispheres and combining them is a great example of a simpler solution.
As the best way of dealing with overhangs is to get rid of them as much as you can, rather than throwing supports everywhere, taking a minute to think about how you can manipulate your model to reduce the number of overhangs can be quite helpful.
Mike started his 3D printing journey with the Anet A8 when it first came out back in 2017, and has been obsessed with 3D printers ever since. Nowadays, he primarily uses his Ender 3 to print functional parts that make his life more convenient whenever possible.