What Can Cause the Object Scale to Be Wrong in Cura?

Using the slicer software is perhaps the most straightforward part of the 3D printing process due to the clean and user-centric interface they offer, as opposed to many other parts of the 3D printing process, such as dealing with the firmware or the electrical components that are a lot more technical in nature.

On the other hand, just as facing issues is entirely possible with any part of 3D printing, it’s possible with slicer software as well, even though it’s rarer and usually more straightforward to resolve due to slicer software being a lot more user-friendly to deal with than other components.

In today’s article, we will be talking about one of the more peculiar problems you can face when you import a model into Cura, where the scale of the model ends up being entirely off, causing the model to become way too small or way too large.

So, what can cause the object scale to be wrong in Cura?

The object scale being wrong in Cura is a result of exporting the 3D model (STL) file with measurements that aren’t millimeters (such as inches), as Cura will automatically interpret the measurements to be in mm due to STL files being unitless and millimeters being the standard in 3D printing.

Moving forward, we will analyze the factors that can cause the object scale to be wrong in Cura with better detail, find out how to fix the problem at hand, and finally, go through the process of disabling the automatic scaling that Cura applies whenever a model is imported.

What Can Cause the Object Scale to Be Wrong in Cura?

The scale of the object being wrong when you import a model into Cura can be confusing, with the model showing up with a much smaller or larger size than what you had in mind when you designed it in CAD software.

Since an STL file, which is the most commonly used 3D model file type for 3D printing, does not convey any information regarding the units used for the design, Cura will automatically assume that 1 unit equals 1 millimeter due to millimeters being the standard in 3D printing.

As a result, in cases where the 3D model is exported with units that aren’t millimeters, such as inches, the STL file will be scaled accordingly to the specified units with no data to tell Cura that the measurements aren’t actually in millimeters.

This will cause the object scale in Cura to be entirely wrong, as Cura won’t possibly be able to tell that the STL file was designed with the intent that one unit equals one inch, as opposed to the standard of one unit equalling one millimeter.

For instance, imagine that you have designed a 3D model with dimensions of 1-inch x 1-inch x 1-inch and exported it with inches as the units, meaning that you essentially intend 1 unit to equal 1 inch.

When you import this file into Cura, Cura will automatically convert 1 unit to 1 millimeter, which will cause your model to be 1 mm x 1 mm x 1 mm instead, when it should have been 25.4 mm x 25.4 mm x 25.4 mm (1 inch = 25.4 mm) according to what you have envisioned.

On the other hand, if you export the same file with millimeters as the units, the CAD software will automatically convert 1 inch to 25.4 units instead of 1 unit, allowing Cura to detect that the model is 25.4 units long on each side, which correctly converts to 25.4 mm (1 inch) on each side.

How to Fix the Issue of Object Scale Being Wrong in Cura?

There are a few different methods you can employ to fix the issue of your object’s scale being wrong in Cura, which should be a straightforward process that won’t take a lot of your time regardless of the method you have decided to use.

The most straightforward way to fix the issue of the object scale being in Cura is to do it directly in Cura, without involving any external software, by following the steps below:

  1. Click the Marketplace button on the top-right corner of Cura.
  2. Click the Mesh Tools entry under the Premium section.
  3. Click the Install button to install the Mesh Tools plugin.
  4. Go through the installation dialogs, and restart Cura.
  5. Click the Extensions tab on the Cura menubar.
  6. Hover over the Mesh Tools option in the dropdown menu.
  7. Click the Mesh Tools settings option.
  8. Click the “Unit for files that don’t specify a unit” dropdown, and choose the intended unit for the model you will be importing.
  9. Import the model into Cura.

Note that the scaling will be applied to all of the models you import until you change the setting, meaning that you should change it back to the default of Millimeter if you are planning on importing models that are exported in millimeters from now on.

Alternatively, if you have designed the model yourself and currently have access to the CAD software, you can re-export the STL file with millimetric units, which will cause the scale to become consistent between what you have designed and what Cura interprets.

As both methods will produce the same exact results, feel free to choose the one that you think is more convenient for you to fix the object scale as quickly as possible.

How to Disable Automatic Scaling in Cura?

While the automatic scaling feature of Cura is reasonably helpful in scenarios where the model is way too small to even see on the screen, there are specific cases where it can cause more inconvenience than good, requiring you to disable it.

To disable the automatic scaling feature in Cura, you can follow the steps below:

  1. Click the Preferences option on the Cura menubar.
  2. Click Configure Cura from the dropdown that appears.
  3. Click the General tab from the left pane of Preferences.
  4. Scroll down to the “Opening and saving files” section.
  5. Uncheck the “Scale extremely small models” checkbox.
  6. Close the Preferences dialog.

With the “Scale extremely small models” setting disabled, Cura won’t apply automatic scaling to any of the models you import anymore.

Wrapping Up 

As the scale of the model plays a vital role in almost every case of 3D printing, and even more so when the model’s dimensions need to be exact, a wrongly scaled model is a critical issue that requires fixing before moving forward with the printing process.

Exporting an STL 3D model file with any unit that isn’t millimeters, such as inches or meters, will cause your model’s scale to be wrong in Cura since STL files don’t carry unit data, causing Cura to assume the measurement of a 3D model in an STL file to be in millimeters.

To fix the issue, you can either re-export the model file in millimeters or use the Mesh Tools plugin in Cura that allows you to specify the units you intend the STL file you’re importing to be designed in and automatically applies the correct scaling based on the unit you have set.

Happy printing!