There are many terms when it comes to 3D printing, but shell thickness is one you may have come across recently. It definitely has its importance in the results of your prints. In this post I will detail how to get the perfect shell thickness settings for your prints.
How do I get the perfect Shell Thickness settings? Getting the perfect shell thickness depends completely on the strength and durability you require for your part. It’s all down to functionality and preference. The minimum amount of walls people tend to use is 2, the highest being 10. Number of Walls * Shell Thickness gives you the overall Wall Thickness.
This is the basic answer on how to get the perfect shell thickness, but there are some useful details that you can learn in the rest of this post. Keep reading to brush up on your knowledge of shell thickness settings.
What Is Shell Thickness?
There are a few names for shells, you have walls and perimeters so you’ve probably seen these terms used interchangeably.
So put simply, shells are the walls of your prints that are exposed to the outside of your model, or just the exterior of your object.
Bottom layers and top layers are also known to be a type of shell because it’s on the exterior or outside of the object.
The main settings you’ll come across is the number of shells and the shell thickness. They both work together to create a certain sized wall around your print. Shell thickness is a combination of your shell width in mm and the number of walls.
If you have a low shell thickness and several walls, it will basically be the same as having a high shell thickness and fewer walls.
How Does Wall Thickness Benefit My Parts?
The main benefit of increasing shell thickness is to add to the strength and durability of a part. These are necessary for prints that serve some kind of functionality, such as a mount, holder or handle.
Adding to your shell thickness is a good alternative to adding tons of material for a higher percentage of infill as found in the video below by CNC Kitchen.
One of the key features you can do for shell thickness is to adjust your prints to have more shell thickness or walls in weaker areas where parts are likely to break.
You do need to keep in mind, adding a large shell thickness for parts that require precision can alter its shape enough to make it unfit for purpose.
It’s not the end of the world because parts can be sanded down to accurate dimensions but this will take extra work, and depending on the part design and complexity, might not be possible.
Larger wall/shell thicknesses creates a sturdy, durable model and also decreases the chance of any leaks. On the other hand, a lower shell thickness can significantly reduce filament used and print times.
How is Shell Thickness Calculated
The usual practice for shell thickness is to have a value which is a multiple of your nozzle diameter.
For example, if you have a nozzle diameter of 0.4mm, you want your shell thickness to be 0.4mm, 0.8mm, 1.2mm and so on. This is done because it avoids print imperfections and gaps occurring.
In terms of figuring out shell thickness, it’s usually calculated to be a value of two nozzle diameters, being 0.8mm for a standard 0.4mm nozzle.
In Cura, the wall thickness is already calculated for you and overridden by line width so when you change your line width input, wall thickness will automatically change to be line width * 2.
When you’re printing with a weaker, brittle material, overall shell thickness can make or break you (excuse the pun), so make sure you’re clued-up on these settings.
To adjust overall shell thickness, you’ll have to change the wall line count setting. Having a shell thickness of 0.8mm means a wall line count of 4 would give you a 3.2mm wall.
How to Get the Perfect Shell Thickness
Now on to getting the perfect shell thickness.
Honestly speaking, there is not one particular perfect shell thickness that will work the best for your prints.
The first thing you should know is that every print has its purpose and functionality. Some are printed simply for looks and aesthetics, while some are printed to under a load or physical bearing.
You need to determine the use of your part before you can identify what the perfect shell thickness would be for you.
If you’re printing a vase, you wouldn’t need such a wide thickness because durability isn’t a necessary characteristic for its use, although you don’t want it to break so you’ll need a minimum.
On the other hand, if you are printing a wall mount bracket, you’ll need the right material, infill and plenty of walls to make the part as strong as possible.
An example is if you print a part with 0% infill and just a 0.4mm wall it will be very weak and easy to break, but add a few walls to it and it will make it a lot stronger.
So this will be trial and error from gaining experience with different shell thicknesses. Once you get the hang of it and understand how it works and looks, you’ll be able to determine the perfect shell thickness with ease.
Is There A Minimum & Maximum Shell Thickness?
You rarely want a wall thickness that is below 1.5mm, because according to IMaterialise who deliver custom 3D prints, these are most likely to break during transit. They recommend a shell thickness of 5mm if it needs to be very solid and durable.
If your model has fragile parts and thin structures such as the limbs on a figurine, shell thickness would help out a lot.
Having a shell thickness too large can also cause issues so watch out for that. This happens with more detailed designs where parts of the print are close to others. At a certain shell thickness, there will be overlap between parts so try to balance it out at a level where you see fit.
If you want your prints to have some flexibility, a thick shell won’t work too well for that as it makes your prints more rigid. Another thing you should know is an overly large wall thickness creates internal stress that can actually result in warping and print failure.
Some slicers have an in-built function to stop people adding too large of a wall to their models.
There is a minimum thickness that a 3D printed part needs to have to be able to hold up at all.
Fictiv found that 0.8mm is the absolute minimum and also the thinner your part’s shell thickness, the higher the chance that something goes wrong during the process.
The reason this happens is because of the nature of 3D printing and its layer by layer process. If melted material doesn’t have a good foundation underneath, it can have trouble building up.
Models with thin walls are more prone to warping and gaps in the print.