How to edit STL files

3D printing has brought a humongous power to the public, a power everyone should crave to take advantage of. Having a 3D printer opens a whole new world or potential that your imagination can shape and push to any given direction.

The single most important thing you should be able to achieve with your 3D printer is designing and printing your own customized item in the exact shape and size you had in mind and in such a way it will solve your problem the best way possible. Today, there are numerous places online where you can easily download STL files for free, but it is likely that you need to edit the STL file to have it work in your favor considering you need it for a specific purpose.

Learning CAD is necessary to edit an STL file and that will be it.

Let’s go ahead and see how you can use these selections of CAD software to edit an STL file.

How to edit STL files using Autodesk 123D Design

Let’s go over to and download a CAD model. I have chosen to download the following model.

When you download the model, it usually comes in a zip file. I did unzip the file and found the STL file which I then opened with 123D Design.

The first thing I would like to do is to make the design editable by converting it into solid using the following feature.

  1. Select the model
  2. Click on Convert Mesh To Solid

Now the model is easily editable. Sky’s your limit!

Let’s FILLET the edges of the model and add a little mark on it.

To Fillet the edge:

  1. Select the FILLET command
  2. Specify the Fillet radius
  3. Select the edges to fillet.

You can make use of the Orbit command to rotate the model to help you select all the internal edges at once before applying the FILLET command. Notice that we have just FIILETed the internal edges but not the external ones.

Now I would like to add the mark on the model, so once printed it will look less generic. What if we add a name, why not the number “45”.

I will create the number, extrude is, place it in such a way I can subtract its geometry from the model to have an imprint on the model.

Let’s EXTRUDE the text.

Select the text and click on the EXTRUDE TEXT command.

Make sure your text is taller than the model.

Now, place the text right on top of the model using the SNAP command.

Make sure that while doing this, you select the down part of the text before selecting the model. If you do select the upper part of the text, it will snap on the model facing the ground.

Now all I need to do is, ungroup the whole, move and center the text and finally subtract it from the model.

Here is the final product

When you are done customizing the model, you need to export it as an STL file so your 3D printing can see it.

And here we have it!

If you want to learn how to model using 123D Design, check the following posts:

How to edit STL files using FreeCAD

FreeCAD is another Free CAD software which you can use to edit any STL file. Using the same file we have used above, we will just go through the process that allows you to start customizing your STL files.

The one crucial step to go through before starting is to convert the model into solid, similarly to what we have done above with 123D Design, but here it takes a bit a number of steps.

Open FreeCAD and select Part Design

Drag the file and drop it in the drawing area. Select Part.

Go on the Model tab, select the model.

Now go on the Part drop down menu and click on Create shape from mesh…

Specify the tolerance.

Delete the Mesh.

Now, use the Advanced Utility to create shapes, select the Solid from Shell Option, select any part of the model and click on Create.

Delete the previous entity.

And you are ready to go. Remember to export your design as an STL file when you are done editing it.