10 Steps to STL File Modification: A Beginner’s Guide

10 Steps to STL File Modification: A Beginner’s Guide

Have you ever downloaded a design from Pinshape and had a great idea for modifying it? Maybe engraving your name or an image into one of the surfaces, or adding some extra details? While .stl files are renowned for being difficult to work with, there is software out there that will help you take back control! Award winning designer James Novak, a.k.a edditive, takes time out from his own blog edditive.com to show us some basic free tools that will have you modifying prints in no time.

What software is available?

The .stl files our 3D printers use are notoriously difficult to modify. It’s a bit like taking a really low-resolution, pixelated image and trying to turn it into a large high-resolution poster. Except in 3D! Much of the CAD software we use to create our designs (whether free or paid) can import and read .stl files, but not many can actually modify them other than perhaps changing the scale or position of them. However there are some great free tools out there that 3D printing enthusiasts need to know about if you want to make any modifications to a .stl file:

Like any software, there is no correct answer to the question “which one is best?” It’s a matter of personal opinion and depends on your previous experience with CAD software. However in this article we will focus on Meshmixer due to its’ clean and simple interface, and the fact that it is specifically designed to modify and repair .stl files, making it easy to learn without complicated menus full of tools you don’t need for this task. And did I mention it’s free?


Tutorial: modifying a .stl file in 10 steps

Today we will walk through a very simple tutorial to delete some text off a downloaded Pinshape model, and then add our own custom text in its place. For this example I will use one of my own models that you can download for free of the ‘Hex Phone Sound Amplifier’ so I don’t inadvertently insult any fellow Pinshaper’s by changing their design! If you want to follow along please download the file onto your computer, or have another .stl file on hand. Also have Meshmixer installed by clicking on the link, and your 3D CAD software of choice as we will need to create the 3D text separately.


1. Model Import: Open up Meshmixer and import the .stl file by going to File>Import. You can click and hold the right mouse button to rotate your model.

2. Plane Cut: To remove text off a flat surface we can use the Plane Cut tool which is found in the Edit menu on the left toolbar. Think of your model like a piece of clay, and the Plane Cut tool as a piece of wire we will use to slice straight through it in a straight line, removing one side of the cut.
edditive james novak pinshape 1

3. Cut and Fill: Use the rotate and arrow sliders to move the Plane Cut tool to be parallel with the model face with text. It takes a little bit of time to adjust to perfection, just keep zooming in and adjusting the angle of the plane by fractions of a degree until you are slicing no more than a hairs-width of material away, including the text (as shown in the image below). Clicking on the squat purple arrow inside of the orbit flips the direction of cutting. By leaving the default settings of the tool (Type: Cut, Fill: DelRefine) and clicking on the Accept button, the tool will remove the text and automatically patch the surface so your model is still watertight. This is the first job done.
edditive james novak pinshape 2

4. Measure: In the current version of Meshmixer (2.9) there is no tool for adding text. So we will need to create a 3D text model, and then import this into Meshmixer. In order to get the size for our text, go into Analysis>Measure and use the Point-to-Point option to measure the size of the face you wish to apply text onto. Turning on the Snap to Edges option helps, and in my experience you may need to try a few different tools to get the measurement you’re looking for – it’s not the best measurement tool. For this model, the face is just over 20mm high, shown on the right of the window.
edditive james novak pinshape 3

5. 3D Model Text: Time to create our text. Use your 3D modelling software of choice to create your custom text, using the height measured in Meshmixer as a guide. For this example I will use another free CAD tool called Tinkercad, which runs completely in your internet browser, so no download required. I won’t go into details of creating this text or this tutorial will quickly turn into a book! The main things are that you consider the dimensions of the text (for this example I’ve made the height 15mm to comfortably fit within the face it will be applied to in Meshmixer), and extruded it 3mm in thickness. Once you’re happy, export your file as a .stl to get it ready for importing into Meshmixer. 
edditive james novak pinshape 4

6. Import: You can now import your text into the original Meshmixer model. Make sure you select the Append option in the pop-up window so that both models will be in the same workspace. You will now have a new Object Browser window available to select between both files, shown top-right in the image below.
edditive james novak pinshape 5

7. Locate: Obviously we now want to rotate and move the text into position. This is easily done from the Edit>Transform menu, bringing up the same arrows as we previously used to Plane Cut. Use the arrows to move the text, and the arcs to rotate it into position. As you get closer and closer, keep zooming in until you can push the text just inside of your chosen surface – if there are any gaps the 2 models won’t properly merge together and may have errors when it comes to 3D printing. If your imported text is too large, the little boxes at the ends of the arrows can be used to scale it as required. Click Accept when complete.
edditive james novak pinshape 6

8. Combine: Just because your 2 models are intersecting on screen doesn’t mean they are actually joined together yet. If you look at the Object Browser window you will still see both models are separate. There are a couple of options to join them together in Meshmixer, and the options will pop up when you select both models together in the Object Browser (using shift-click) and then the Edit menu. Technically we should be using Boolean Union to merge them together (or Boolean Difference if you wanted the text to cut into the surface as an embossed detail) however the result seems to be very low resolution and will change the text. Instead we will use Combine, which still won’t properly join the shapes together, but will merge them into a single file. For many 3D printers and software this is enough and you could export this now as a .stl and get 3D printing. However when you’re sharing files on Pinshape or other sites it’s important to make sure your files are in the very best condition so everyone can 3D print them no matter what printer or software they’re using. And it only takes a few extra clicks to get this right.
edditive james novak pinshape 7

9. Make Solid: Now that our objects are combined into a single file, we can use Edit>Make Solid to properly merge them together and also control the resolution of the mesh. The default settings may shock you when the preview is generated with a lot of your crisp edges becoming soft and low resolution. By increasing the sliders for Solid Accuracy and Mesh Density you can increase the resolution. Just click the Update button to refresh the preview model. When you’re happy with the detail you can Accept the model – just keep in mind the higher your resolution, the larger the final .stl file size! In the Object Browser you will also note that the original model (before using Make Solid) is still available, just hidden from view so you can always go back to this one if you want to change the detail by clicking on the eye symbol.
edditive james novak pinshape 8

10. Export: Finally you are ready to use the Export function on the left menu. Make sure you check that the file type is a STL Binary Format, not STL ASCII Format which typically results in a much larger file size.
edditive james novak pinshape 9

With these 10 steps you should now have the confidence to begin customising the designs you download from Pinshape or anywhere else. There are plenty of other tools available in Meshmixer, or indeed the other programs mentioned earlier for manipulating .stl files, but these might need to wait for another day. If you’re interested in finding out more, there is a great library of video tutorials called Autodesk Meshmixer 101 that should get you customising like a pro in no time! 

Questions? Comments? We’d love to hear from you! 

If you have any questions or things to add to this tutorial, please let us know in the comments below! We hope this tutorial helped. Tune in next time to learn about how to repair your STL files!  


stl files for 3d printing button

The Pinshape community is talking about us! Send your testimonials to [email protected].  

Editor’s note: Karen, your community manager, here! I wanted to drop a note on how quickly this tutorial helped me on my way to customizing the sound amplifier. Attaching a screenshot— this took me less than 20 minutes to make. I have never used Meshmixer before, but I had briefly touched Tinkercad. I simply used the pre-generated letters on Tinkercad to spell out my name and voila! Surprisingly easy tutorial 🙂 

Screen Shot 2015-08-17 at 3.38.12 PM




Pinshape is a 3D printing community and marketplace where makers from all over the world can find and share their next great 3D print and help each other get the best results from their 3D printers.