How to Convert STL to STEP Using Free Software (Short Tutorial) 07:20
Using free software, we can convert a 3D scan (STL) into a CAD format (STEP). This process is called reverse engineering. We will reconstruct a solid model based on a 3D scan. This is not an automatic process, but a manual reconstruction. For this tutorial, we will use Netfabb (version 7.4.0) or Netfabb (current version) to measure the 3D scan. And the current version of FreeCAD (free CAD software) to redesign the part in CAD.
Table of Contents
This tutorial covers the five basic steps to perform reverse engineering using FreeCAD and Netfabb. This tutorial is intended for advanced FreeCAD users. We have also prepared a 120 min tutorial video, which takes you, in detail, through each step.
With FreeCAD, you can design in CAD, and thus, create a solid model (STEP format).
The broken part, which serves as an example project, is a fuel sensor from a 50-year-old car. First, a 3D scan was made using the professional 3D scanner, Artec Space Spider. Then, a reverseengineered 3D scan was created using parametric modeling in FreeCAD.
Step 1: Measure the 3D Scan in Netfabb and create a reference sketch in FreeCAD
In this first step, a circle is defined using FreeCAD, which will help us align the 3D scan correctly.
Step 2: Correct Alignment (Placement) of the 3D Scan in FreeCAD
Align the 3D Scan optimally along the X, Y and Z-axes. This is done in the “Sketcher” workbench.
Step 3: Change the Transparency of the 3D Scan in FreeCAD and Create a Profile
Adjust the 3D scan to make it semi-transparent to allow for designing directly on it.
Step 4: Hide Areas of the 3D Scan and Sketch on the Cross-section.
The following steps can be performed in the “Mesh Design” workbench.
Step 5: Connect Profiles with a Loft.
Depending on the complexity of the part, many different profile sketches must be created to determine the outer shape. Continue working in the “part design” workbench. The profiles are connected with a loft to form a closed solid.
Step 6: Connect the Individual Bodies with the Boolean Operation and Export Them as a STEP File.
In this last step, connect the single bodies and export them as a STEP file. For this phase, continue working in the workbench “Part”. Not all bodies need to be created with lofting. Some can be created with very simple geometry.
Step 7: Compare the Newly Constructed Solid Model (STEP) with the Original 3D Scan (STL)
Create a report to compare the newly generated solid model in FreeCAD with the original 3D scan. This is a deviation analysis. To create this analysis, we used the free software GOM Inspect.
Explanation of the Colors
Green means there is hardly any deviation between the original 3D Scan and the newly
created solid model.
Red means that the new solid model overlaps the original 3D Scan at this point.
Blue means the new solid model is under the original 3D Scan.
Project Files Available for Download
We have prepared all project data for download, including the original 3D scan, the CAD solid model and the deviation analysis.
The reverse engineering was very successful. There are differences between the 3D scan and the CAD model, which we have created, but the original part was heavily deformed, and our reconstruction is therefore much better than the original.
Do you need help converting an STL to a STEP file?
Holocreators offers professional 3D-scanning and reverse engineering services. We would love to help you with converting your files from STL to STEP. Please call us at +49 40 481133 or send an email email@example.com
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Reverse engineering is required whenever a 3D scan (STL format) needs to be converted into a CAD model (STEP format). We will give you a brief overview of three different reverse engineering techniques.
A NURBS model consists of points connected by curves. A polygon mesh consists of thousands or millions of small triangles. CAD surface models are usually created using NURBS surfaces, while 3D scans are typically exported as a polygon mesh. The conversion from a polygon mesh to a NURBS model is called "reverse engineering".
Reverse engineering enables us to create a copy of an object. For this purpose, the part is 3Dscanned, then the 3D scan data is converted into a CAD format, and finally, the part is manufactured. All these steps result in noticeable deviations. If an error adds up over multiple steps, then we call this error propagation.