How to Assemble STP Files in FreeCAD

So, you’ve got a bunch of STP files and want to put them together in FreeCAD? Awesome! Don’t worry if you’re new to CAD software—FreeCAD is open-source and surprisingly friendly when you know where to look. Today we’re going to make sense of loading, moving, and assembling STP files like a pro.

TL;DR (Too Long; Didn’t Read):

FreeCAD lets you import STP files and arrange them into working assemblies. Use the Assembly or A2plus Workbench for connecting parts with constraints. You can move and rotate components easily before locking them into position. It’s easier than it sounds—once you try it, you won’t turn back!

What’s an STP File, Anyway?

STP (or STEP) files are a standard format for 3D models. They store geometry info—just shapes, no features or history. Think of it like LEGO bricks: you know what they look like, now you’ve just gotta snap them together!

Step 1: Install FreeCAD

If you haven’t already, download FreeCAD from the official site. It’s free and works on Windows, macOS, and Linux.

Make sure you get version 0.20 or later. Why? Because newer versions offer better support for STP files and more stable Assembly workbenches.

Step 2: Install the Assembly Workbench

FreeCAD doesn’t ship with fully featured assembly tools by default. But you can add them! Here’s how:

1. Open FreeCAD.
2. Go to Tools → Addon Manager.
3. Find and install the A2plus or Assembly4 workbench. (We’ll use A2plus in this guide—it’s beginner-friendly.)

Wait a moment while it downloads and restarts FreeCAD if necessary.

Step 3: Create a New A2plus Assembly

Once A2plus is installed, switch to it using the drop-down menu in the top toolbar.

1. Click on Create a new A2plus assembly (the blue gear icon).
2. It’ll make a new document for your assembly. Save it right away!

Now you’re all set to bring in some parts.

Step 4: Import Your STP Files

Here’s where the fun begins. Start loading your 3D parts:

1. Click on Add a part from external file (the green Lego brick with a plus sign).
2. Select your STP file. Poof! It appears in the model space.
3. Add more STP files the same way until you’ve got everything you need.

Your parts might load in random orientations. Time to play puzzle master!

Step 5: Move the Parts Around

Each part you loaded is floating in space. Let’s position them roughly before we glue them in place.

1. In the model tree, find your part (usually named like “Import_001”).
2. Right-click and select Transform.
3. Use the arrows and circles to move and rotate.

Tip: Use mouse scroll to zoom and Shift + right-click to pan around.

Once each part is roughly where it belongs, we can start locking them together.

Step 6: Add Constraints

Constraints are rules that stick parts together. For example, “make this face touch that one,” or “keep these holes aligned.”

Here are the basic ones you’ll use:

• Plane coincidence – makes two surfaces flush.
• Axis coincidence – aligns holes or pins.
• Distance – sets a fixed gap between parts.

To add a constraint:

1. Click the corresponding constraint tool in the A2plus toolbar (hover over icons to get tooltips).
2. Click the surfaces or edges you want to connect.
3. Confirm the constraint and watch the magic happen.

Keep going until your parts are fully assembled. If something won’t move the way you expect, check for missing or conflicting constraints.

Step 7: Save and Celebrate 🎉

Once everything looks good and behaves properly, save your assembly file. You can now export the whole thing as a new STP file, STL for 3D printing, or even create detailed drawings.

Bonus Tips for Smooth Assembling

• Use simple names – Rename your parts in the tree to avoid mistakes, like “BasePlate” or “GearShaft”.
• Use shaded view – Press V → D → S in sequence for shaded faces. It helps to see overlaps.
• Lock at least one part – Usually the base part. Use the “Fix part in place” tool (the anchor icon).
• Use the measure tool – Right-click the workspace and turn on the Measure tool to check gaps.

Common Pitfalls

Everyone makes mistakes. Avoid these common ones:

• Importing meshes instead of STP: Stick to STP/STEP files, not STL for precise geometry.
• Over-constraining: Too many constraints = confused assembly. Less is more!
• Forgetting to anchor one part: Then everything floats away. Always fix one piece in place.

Advanced Stuff (If You’re Feeling Brave)

If you get comfy with assemblies, explore these extras:

• Assembly4 workbench – More powerful. Supports hierarchy and parametric constraints. Bit more complex though.
• Creating exploded views – Cool for documentation or presentation. Use transformations + screenshots.
• Linking parts with spreadsheets – Want fancy customization? Control dimensions using FreeCAD’s Spreadsheet tool.

Conclusion

Assembling STP files in FreeCAD is like adult LEGO—with superpowers. You import your shapes, position the parts, slap on some constraints, and just like that—your virtual machine is born!

The more you practice, the smoother it gets. So go ahead—grab some STP files and start building. Who knows? You might end up designing the next Mars rover! 🚀