PLA, ABS & PETG Shrinkage Compensation in 3D Printing – A How to
Although 3D printing produces pretty detailed models that look almost identical to the CAD image, the dimensional accuracy and tolerance aren’t perfectly identical. This is something called shrinkage, which happens in 3D prints that you probably don’t even notice.
I thought about just how much shrinkage occurs in 3D prints, an ideal question for those who want to create functional objects that require tight tolerances, so I decided to find out and share it with you guys.
In this article, we’ll cover what shrinkage is, how much your 3D prints are likely to shrinking by, and some good shrinkage compensation to use.
What Is Shrinkage in 3D Printing?
Shrinkage in 3D printing is the reduction in size of the final model due to temperature changes from the melted thermoplastic, to the cooled extruded material layers.
During printing, the extruder melts the printing filament to create the 3D model, and the material expands during this process. After layers start to cool right after being extruded, it causes the material to increase in density, yet reduce in size.
Most people won’t realize that this is happening until they have a model which requires a little more dimensional accuracy.
Shrinkage is not a problem when printing aesthetic models like artworks, vases, and toys. When we start moving to objects that have tight tolerances like a phone case or a mount connecting objects together, shrinkage is going to become an issue to solve.
It occurs in almost every 3D printing process due to the temperature variations involved. But the rate at which it occurs varies depending on a few factors.
These factors are the material used, temperature, printing technology, and curing time for resin prints.
Out of all of these factors, perhaps the most important factor affecting shrinkage is the material used.
The type of material used will have influences on how much the model will shrink.
The printing temperature and cooling speeds are also important factors. Shrinkage can occur if the model is printed at a high temperature or cooled too fast, meaning that higher temperature plastics are more likely to shrink.
Rapid uneven cooling can even lead to warping, which can damage the model, or ruin the print altogether. Most of us have experienced this warping, whether it comes from drafts or just a really cold room.
Something that helped with my warping that I recently implemented is using a HAWKUNG Heated Bed Insulation Mat under my Ender 3. Not only does it help with warping, it also speeds up heating times and keeping a more consistent bed temperature.
Finally, the type of printing technology used also determines the extent of shrinkage found in the model. Cheaper technologies like FDM usually cannot be used to make high-quality parts with tight tolerances.
SLS and metal jetting technologies justify their high price tag by producing accurate models.
Luckily, there are plenty of ways to account for shrinkage, allowing us to produce dimensionally accurate parts without too much hassle, though you need to know the right techniques.
How Much Do ABS, PLA & PETG Prints Shrink?
Like we mentioned earlier, the rate of shrinkage depends heavily on the sort of material used. It varies from material to material. Let’s take a look at three of the most widely used 3D printing materials and how they hold up to shrinkage:
PLA is an organic, biodegradable material also used in FDM printers. It is one of the most popular materials used in 3D printing because it is easy to print with and also non-toxic.
PLA suffers from little shrinkage, hearing shrinkage rates of between 0.2%, up to 3% since it’s a lower temperature thermoplastic.
PLA filaments do not need high temperatures to be extruded, the printing temperature is around 190℃, which is smaller than that of ABS.
Shrinkage in PLA can also be reduced by printing in an enclosed environment or simply scaling up the model to compensate for shrinkage.
This works because it reduces those rapid changes in temperature, and reduces the physical stress on the model.
I think these shrinkage rates depend on the brand and manufacturing process, and even the color of the filament itself. Some people found that darker colors tend to shrink more than lighter colors.
ABS is a petroleum-based printing material used in FDM printers. It is used extensively because of its high strength, heat resistance, and versatility. It can be found in anything from phone cases to Legos.
ABS does have a really high shrinkage rate, so if you need dimensionally accurate 3D prints, I’d try to avoid using it. I’ve seen people comment on shrinkage rates being anywhere from 0.8%, up to 8%.
I’m sure these are extreme cases, and you would be able to reduce that with the right setup, but it is a good show to illustrate how bad shrinkage can really get.
One of the main ways to reduce shrinkage is to print at the right heated bed temperatures.
Using a correctly calibrated heated bed helps with first layer adhesion and also helps to prevent the bottom layer from cooling too much faster than the rest of the print to avoid warping.
Another tip for reducing shrinkage is to print in an enclosed chamber. This isolates the 3D print from outside air currents ensuring it does not cool unevenly.
The enclosed chamber keeps the print at a steady near plastic temperature until printing is completed, and all sections can cool at the same rate.
A great enclosure that thousands of people have used and enjoyed is the Creality Fireproof & Dustproof Enclosure from Amazon. It keeps a constant temperature environment and is very easy to install & maintain.
On top of that, it provides more safety in terms of fires, reduces sound emissions, and protects from dust build up.
PETG is another widely used 3D printing material due to its phenomenal properties. It combines the structural strength and toughness of ABS with the ease of print and no-toxicity of PLA.
This makes it suitable for use in many applications requiring high strength and material safety
At 0.8%, PETG filaments have the lowest shrinkage rate. 3D models made with PETG are relatively dimensionally stable when compared to others. This makes them ideal for making functional prints that have to conform to somewhat strict tolerances.
To compensate or reduce shrinkage in PETG prints, the model can be scaled up by a factor of 0.8% before printing.
How to Get the Right Shrinkage Compensation In 3D Printing
As we’ve seen above, shrinkage can be reduced in several ways. But, the fact remains that no matter how much is done, shrinkage cannot be eliminated. That’s why its good practice to try and account for the shrinkage when preparing the model for printing.
Getting the right shrinkage compensation helps in accounting for the reduction ins size of the models. Some printing software comes with presets that automatically do this for you, but most of the time, it has to be done manually.
Calculating the sort of shrinkage compensation to be applied depends on three things, the material being used, the printing temperature, and the geometry of the model.
All these factors combined will give an idea of how much the print is expected to shrink and how to compensate for that.
Getting the right shrinkage can also be an iterative process, otherwise known as simple trial and error. The rate of shrinkage might even vary across different brands of the same type of material.
So, a great way to measure and quantify shrinkage is to first print a test model and measure the shrinking. The data you get can then be used to create an mathematically-sound shrinkage rate compensation.
A great way to measure shrinkage is by using this Shrinkage Calculation Object from Thingiverse. One user described it as “One of the best general calibration tools around”. Many other users share their thanks with the maker of this CAD model.
The steps are as follows:
- Print the test part using your filament of choice, and slicer settings you intend to use.
- Measure and input into the spreadsheet (mine is shared at https://docs.google.com/spreadsheets/d/14Nqzy8B2T4-O4q95d4unt6nQt4gQbnZm_qMQ-7PzV_I/edit?usp=sharing).
- Update slicer settings
You want to use that Google Sheet and make a new copy that you can edit yourself from fresh. You’ll find the instructions on the Thingiverse page for more details.
If you want a really accurate compensation, you can actually run the iteration twice, but the maker says that just one iteration was enough to get them within a 100um (0.01mm)tolerance over a 150mm part.
One user said he simply scales his models to 101%, and it works pretty well for him. This is a really simple way of looking at things, but it can be successful for quick results.
You can also make use of a setting called horizontal expansion which adjusts the size of your 3D prints in the X/Y dimension, to compensate for changes in size as the model cools and shrinks.
If you are creating the models yourself, you can adjust the tolerances on the model itself, and with more practice, you’ll start to be able to guess the correct tolerances per your specific design.