For most uses in 3D printing, dimensional accuracy and tolerances doesn’t have a massive significance in our models, especially if you are 3D printing for cool looking models or decoration.
On the other hand, if you are looking to create functional parts that require high dimensional accuracy and precision, then you want to take a number of steps to get there.
SLA 3D printers usually have the best resolution, which translates into better dimensional accuracy and tolerances, but a well-tuned FDM printer can still do great. Calibrate your printing speed, temperature, and flow rates to get the best dimensional accuracy. Make sure to stabilize your frame and mechanical parts.
The rest of this article will go into some extra detail on getting the best dimensional accuracy, so keep reading to find out more.
What Factors Affect Your Dimensional Accuracy in 3D Printing?
Before moving to the factors which are affecting the dimensional accuracy if your 3D printed parts, let me just throw some light on what exactly dimensional accuracy is.
It simply refers to how well a printed object matches the size and specifications of the original file.
Below is the list of factors which have an impact on the dimensional accuracy of 3D prints.
- Machine Accuracy (resolution)
- Printing Material
- Object Size
- Impact of First Layer
- Under or Over Extrusion
- Printing Temperature
- Flow Rates
How to Get the Best Tolerances & Dimensional Accuracy
3D printing requires a good level of accuracy when printing specialized parts. However, if you want to print with high-level dimensional accuracy, the following factors will help you to get there, along with the mentioned steps.
Machine Accuracy (Resolution)
The first thing you want to look at when you are trying to improve your dimensional accuracy is the actual resolution that your 3D printer is limited to. Resolution comes down to how high the quality of your 3D prints can be, measured in microns.
You’ll usually see XY resolution and layer height resolution, which translates to how precise each movement along the X or Y axis can be.
There is a minimum of how much your print head can move in a calculated fashion, so the lower that number, the more accurate the dimensional accuracy.
Now when it comes to the actual 3D printing, we can run a calibration test which you can use to figure out how good your dimensional accuracy is.
I’d recommend printing yourself an XYZ 20mm calibration cube (made by iDig3Dprinting on Thingiverse) then measuring the dimensions with a pair of high quality calipers.
The stainless-steel Kynup Digital Calipers is one of the highest rated calipers on Amazon, and for good reason. They are very accurate, up to an accuracy of 0.01mm and very user-friendly.
Once you’ve 3D printed and measured your calibration cube, depending on the measurement, you will need to adjust your steps/mm directly in your printers firmware.
The calculations and adjustments you’ll need goes as follows:
E = expected dimension
O = observed dimension
S = current number of steps per mm
(E/O) * S = your new number of steps per mm
If you have a value that is anywhere between 19.90 – 20.1mm, then you’re in a very good space.
All3DP describes that:
- Greater than +/- 0.5 mm is bad
- Less than +/- 0.5 mm is average
- Less than +/- 0.2 mm is good
- Less than +/- 0.1 mm is fantastic
Made your adjustments as necessary, and you should be closer to your goal of getting the best dimensional accuracy.
- Use a 3D printer which has high resolution (lower microns) in the XY axis and the Z axis
- SLA 3D printers usually have better dimensional accuracy than FDM printers
- In terms of the Z axis, you can get resolutions all the way down to 10 microns
- We usually see 3D printers with resolutions of 20 microns up to 100 microns
Depending on the material you are printing with, there can be shrinkage after cooling, which will decrease your dimensional accuracy.
If you are changing materials and aren’t used to the levels of shrinkage, then you want to run some tests to figure out how to get the best dimensional accuracy in your prints.
Now, you can go for:
- Run a calibration cube test again if you are using a different material to check shrinkage levels
- Scale your print depending on the level of shrinkage in the mentioned print.
Similarly, the object’s size is significant because large objects often create complex problems, and inaccuracy is rampant sometimes in such large objects.
- Go for smaller objects, or divide your bigger object into smaller parts.
- Separating the bigger object into smaller parts increases the dimensional accuracy of each part.
Check Movement of Components
Different parts of the machine play a role in the 3D printing process, so every part needs a check before you go for printing.
- Check all the tension belts and tighten them just to be sure.
- Make sure your linear rods and rails are all straight.
- You should also make sure your 3D printer is well-maintained and use a little oil on linear rods & screws.
Improve Your First Layer
The very first layer is like that first question in the exams; if it goes well, everything will stay fine. Similarly, your first layer can have a long-lasting impact on the print model in terms of dimensional accuracy, if not handled properly.
If you have kept the nozzle too high or too low, it will impact the thickness of the layers, affecting the print drastically.
What you need to do along with managing the dimensional accuracy is:
- Make sure your nozzle is a good distance away from the bed to get a perfect first layer
- I would definitely test out your first layers and whether they come out well
- Level your bed properly and ensure that it is level while heated so you can account for any warping
- Use a glass bed for a very flat surface
Temperature plays a significant role in getting the desired accuracy. If you are printing at a high temperature, you may witness more material coming out, and it is taking more time to cool.
This can affect the dimensional accuracy of your prints, since the previous layer that hasn’t cooled can be affected by the following layer.
- Run a temperature tower and find your optimal temperature which reduces print imperfections
- Usually slightly reducing your printing temperature (around 5°C) does the trick
- You want to be using the lower temperature possible that doesn’t result in under-extrusion.
This will give proper time for your layers to cool, and you will get a smooth and appropriate dimensional accuracy.
Compensate While Designing
After you have set the dimensional accuracy of the machine, you should be on track, but in some cases you can get dimensions which aren’t as accurate as you thought.
What we can do is take into account the inaccuracy of certain parts design-wise, and make changes to those dimensions before 3D printing it.
This only comes into play if you are designing your own parts, but you can learn how to make adjustments to existing designs with some YouTube tutorials or just spending time learning the design software yourself.
- Check the printing capacity of your machine and set your designs according to it.
- If your 3D printer can only print up to a certain resolution, you can increase the size of important sections by a little
- Scale other designer’s models to fit your machines’ tolerance capacity.
Adjust Flow Rate
The amount of filament coming out of the nozzle is directly proportional to how effectively your layers are getting deposited and cooling down.
If the flow rate is slower than optimal, it can leave gaps, and if it is high, you can witness excessive material on the layers such as blobs and zits.
- Try to find the right flow rate for the printing process.
- Adjust in small intervals using a Flow Rate Test then see which flow rate gives you the best results
- Always keep an eye for over-extrusion while increasing flow rate and under extrusion while lowering the flow rate.
This setting is great to combat under or over-extrusion in your 3D prints, which can definitely negatively affect your dimensional accuracy/
Horizontal Expansion in Cura
This setting in Cura allows you to adjust the size of your 3D print in the X/Y axis. If you have a 3D print with holes that are too big, you can apply a positive value to your horizontal offset to compensate.
Vice versa, for smaller holes, you should apply a negative value to your horizontal offset to compensate.
The main role played by this setting is:
- It compensates for the change in size that happens when the shrinks as it cools.
- It helps you to get the exact size and accurate dimensions of your 3D print model.
- If the print model is smaller than keep a positive value and, if it’s large, go for a smaller value.
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