Tutorial – Holocreators

How to convert STL to STEP with free software?

Swann Rack — Mon, 15 Jun 2020 21:33:09 +0000

Introduction

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 Netfabb (version 7.4.0) or Netfabb (current version) you can optimally measure the 3D scan (STL file). (It is also possible to measure directly in FreeCAD, but it works better in Netfabb).
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.

This is the original 3D Scan (STL format) of the tank sensor part. It was created with a professional 3D
scanner (Artec Space Spider). We have prepared the 3D Scan for download here.

After reverse engineering using parametric modeling in FreeCAD, the finished solid model (STEP
format) looks like this. We have prepared the CAD file for download here.

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.

The original 3D scan is imported,”professional-3d-scan-with-artec-space-spider-tankgeber-part.stl”,
into Netfabb. We have prepared the 3D Scan for download here.

Click on the button “New Measuring”.

Click on “Measure Radius”. The button “3 points on circle” must be activated.

Select the outer edge of the flange. Netfabb will automatically output the outer diameter.

The outer diameter of the flange is 75.97mm—round up to 76mm.

Import the file “professional-3d-scan-with-artec-space-spider-tankgeber-part.stl” into FreeCAD and
activate the workbench “Sketcher”. Click on the button “Create a circle in the sketch”.

Click on the button “Fix the radius of a circle or an arc”.

Enter the radius of the diameter. So 76mm/2 FreeCAD will automatically calculate the radius of
38mm. The reference circle sketch is now ready.

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.

In the lower-left hand corner, click on the button “Data”.

Click on the three dots next to the “Placement” button.

Activate the checkbox “Apply incremental changes to object placement”.

Switch to a side view and rotate the 3D Scan incrementally until it is aligned perpendicular to the Xaxis.

In the end, it should look like this.

Change the view and repeat the process for the Y-axis.

Finally, switch to a top view and move the 3D Scan until it is in the center of the circle. The 3D Scan is
now optimally aligned in the FreeCAD coordinate system. This will simplify the CAD modeling process.

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.

The key combination CTRL+D opens a window in which we can set the “Transparency”.

If CTRL+D does not work, you can set the “Transparency” directly in the menu’s lower-left hand
corner.

Click on “create new sketch” to enter the ”sketcher” workbench.

Select the XY layer.

Design on the cross-section of the flange.

Click on “fix a length of a line or the distance between a line and a vertex “.

Define the dimension between the edge of the flange and the center. The radius is 76mm/2=38mm. A
frequent change between Netfabb and FreeCAD is necessary until all constraints are defined for the
sketch.

When all constraints have been defined, the sketch will turn to green.

In the workbench ”Part Design” click on “Revolve a selected sketch”.

After revolving, the basic geometry of the flange is complete. Further sketches optimize the shape.

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.

Click on the button “Cut a mesh with a picked polygon”.

With the outlined blue area, we define the section of the 3D Scan to hide.

After we have completed the selection, right-click and select “Inner”.

Switch to the “Sketcher” workspace and click on “Create new sketch”.

Select the XY plane.

In the “Position” menu, change the Z-axis until the plane is at the same height as the cut edge.

The result should look like this.

We switch to the top-view and sketch on the cross-section of the 3D Scan.

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.

These three profiles are to be connected to form a loft.

For the sake of simplicity, first concentrate on the outer shape.

Click on ” loft a selected profile through other profile sections.”

The result of the lofted profiles should look like this.

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.

First, select the flange body.

Then select all other bodies.

Click on “Boolean operation with two or more bodies” to connect all bodies.

The result is the finished CAD solid model.

The solid model can now be exported as a STEP file. You can download the finished STEP file here.

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 software Zeiss Inspect.

This picture shows the deviation between the 3D Scan (STL) and the solid model (STEP) in mm. You
can download the deviation analysis here.

The different colors show the degree of deviation.

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.

Summary

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 3D scanning services, 3D scan-to-CAD conversion services (STL to STEP), 3D modeling services, and CAD design 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 info@holocreators.com

The post How to convert STL to STEP with free software? appeared first on Holocreators.

How to 3D scan for free?

Swann Rack — Mon, 15 Jun 2020 15:38:48 +0000

Holocreators is a 3D scanning company. We offer you a professional 3D scan service with an
accuracy of up to 0.005mm. We’d love to help you with your project. Call us at +49 40
481133 or write us an email: info@holocreators.com

Left – Free scan / Right – Professional scan

With this tutorial, we show you all the steps to create a free 3D scan. As an example, we 3D
scan a metal part from the fuel tank of a car. The part is called “Tankgeber” (fuel sensor):

To follow this tutorial, you need these free software packages:

Step 1: Manual Measurement

Measuring a metal part with a caliper

First, we measure our part (“fuel sensor”) manually. To minimize errors, we measure three
times with the caliper and determine the average value. This way, measurement outliers are
eliminated. We determine an average diameter of 76.2mm. This is the reference dimension,
which will be very important later on.

Photogrammetry (that’s the name of this 3D scanning technique) has the disadvantage that
it can’t produce correct measurements. Therefore, we need a reference measurement.

The reason is that the 3D model is calculated from photos, and the computer does not know
how big the part actually is.

Step 2: Taking Pictures of the Part

We take (at least 100) pictures of the part with a mobile phone camera from different angles
and perspectives

We place the part on a box and take lots of pictures from different angles and perspectives
with a cell phone—the more images, the better. Take at least 100 photos.
Good lighting is important. Photogrammetry works best with diffuse lighting. Fluorescent
tubes work great. Shadows have a negative effect on the photogrammetry process. The
object we want to 3D scan should have distinctive geometric features and should not be
reflective. Use spray chalk, if it’s too reflective. Take two photosets—one with the part
upright and one inverted to capture the interior features

Step 3: Creating the 3D Model (photogrammetry) in Meshroom

We import the photos to Meshroom

Next, import all the photos into the Meshroom software— simply by drag-n-drop. Press start
and the software does the rest. After the software has calculated the 3D model, the data is
exported as an OBJ file. (OBJ is a very similar format to STL and can be processed in the same
way.)

After we click the “Start” button, Meshroom asks where to save the MeshroomCashe folder

Many users have the problem that they cannot find the 3D model (OBJ format) created by
Meshroom.
When we click the “Start” button in Meshroom, we are asked where the cache folder should
be created. The project files are then stored in this folder. The “MeshroomCashe” folder
contains the subfolder “Meshing,” where the 3D scan is saved as an OBJ 3D model.

In the subfolder “Meshing” the 3D model is stored in OBJ format

Step 4: 3D Scan Cleanup in Meshlab

Select “Select Faces in a Rectangular Region” in Meshlab

Import the 3D scan (OBJ format) into Meshlab. Remove all unneeded geometry not wanted
in the 3D Scan. For this, use the function “Select Faces in a Rectangular Region”. Select
unwanted areas in red and then press the “delete”.

Cut away unneeded geometry

Once the 3D scan cleanup is complete, i.e. removed all unwanted geometry, we export the
3D model in STL format. Repeat this process also for the inside 3D scan.

Step 5: Measuring and Resizing in Netfabb

In Netfabb, measure the 3D scans and adjust the size using the reference diameter
determined earlier by manually measuring the part. To do this, import the STL file into
Netfabb and click on the “new measuring” button.

In Netfabb, click on the “New measuring” button

With Netfabb, measure the outer radius of the flange from the 3D scan

Determine the outer radius of the flange. It has a diameter of 6.98mm in the 3D scan.
Initially, manual measurement produced a value of 76.2mm. Therefore, we divide
76.2mm/6.98mm and get a scaling factor of 10.91. With this factor, we rescale the 3D model
to get the part’s original size.

Enter the new scaling factor (10.917) into Netfabb

Step 6: Realignment of Both 3D Scan Halves in Meshlab

Import both rescaled 3D scan halves back into Meshlab to line up and connect them
correctly. This process is called “alignment.”

Import both 3D scans into Meshlab

Click on the yellow “Align” icon

Select the upper 3D scan and click on “Glue Mesh here”

Select matching points on both 3D scans

To help the software fit the 3D models correctly, select at least three matching points on
both 3D scans. Then click on “Process,” and the software aligns both 3D scans.

Using the function “Select Faces in a Rectangular Region” remove overlapping geometry

Both 3D scans still have overlapping areas. Use the function “Select Faces in a Rectangular
Region” to remove this duplicated geometry.
Finally, right-click on the upper 3D scan in the right list and select “Flatten Visible layers”.
This function merges both 3D Scan halves.

Now the 3D scan of our part (“tankgeber”) is completed.

Step 7: Checking the Accuracy of the 3D Scan in Zeiss Inspect

We want to check how accurate our free 3D scan is. Therefore, we have 3D scanned the
same part with the professional 3D scanner Artec Space Spider. In the software Zeiss
Inspect, we compare both 3D scans and check the accuracy of the free 3D scan. With this
data, we created a deviation analysis.

Result: Our free 3D scan is pretty accurate. On average, it deviates only 0.2mm from the
professional 3D Scan.

With a deviation analysis, we determine the 3D scan accuracy in Zeiss Inspect

Download of the Project Data

We have provided both the free 3D scan and the professional 3D scan for you to download.
The deviation analysis, which compares both 3D scans, is also available for download:

Conclusion

It is very impressive that we achieved this 3D scan result with only a mobile phone camera
and free software. Accuracy of 0.2mm was previously reserved for professional 3D scanners.
Nevertheless, the professional 3D scanners have their merits. They are calibrated and
guarantee a level of accuracy, which is very important when measuring critical parts. Also,
the 3D scan is much faster with a professional 3D Scanner. The free 3D scan required about
3 hours, while the professional 3D scan was completed 15 minutes.

Do you need help with a 3D Scan?

Holocreators offers 3D scanning services, 3D scan-to-CAD conversion services (STL to STEP), 3D modeling services, and CAD design services. We are happy to support you with your projects. If your
project requires the use of professional 3D scanners and a guaranteed accuracy from 0.1mm
to 0.005mm, then please feel free to call us at +49 40 481133 or write us an email:
info@holocreators.com

The post How to 3D scan for free? appeared first on Holocreators.