Reverse Engineer of Damaged gear

How can a damaged gear like the one below be replicated within 3D Design software, when 75% of the teeth are either damaged or missing?

The answer is 3D scanning and reverse engineering. Using 3D Scanning technology the gear can be scanned, then the scanned data can be inputed into 3D design software where the teeth that are intact can be arrayed in the exact PCD (Pitch Circle Diameter) of the teeth to generate the new 3D model.

The challenges with 3D scanning is that the object that requires scanning needs to have distinguished features to pick up, flat or symmetrical objects are very difficult to scan, one options is to use reflective 3D markers that is supplied with the Einscan range, or an even easier and quicker option is to add random objects that can be placed onto the gear, for this exercise we used these:

3D Printed parts assist 3D scanning

The 3D scanner capable of scanning the gear at an accuracy of 50 microns (that’s 0.05mm) is the Einscan Pro HD . Using structured light technology the scanner projects structured light from either side of the scanner, then the camera at the centre captures the shape of the deformed light on the surface of the object.


How structured light 3D scanners work

The object is scanned using a turntable and tripod, this is an optional extra with the Einscan HD called the industrial pack, which is incredibly efficient. The part is placed onto the turntable then the turntable is set to rotate and stop every 36°, so after 10 increments the part is fully scanned:


3D Parts used in scanning

The random 3D printed parts can then be easily deleted:

3D parts deleted

The information captured by the camera is then sent back to the Einscan software. Using triangulation algorithm, the objects depth and measurements are calculated to generate an accurate 3D surface. 

3D scanned object polygons

In most 3D scan cases the scanned objects are flipped/rotated to scan a full 360 of the part, but in this circumstance only the external profiles of the gear is required. Then, the scanned STL file is exported to Geomagics. By using the function “Create by Section” a plane can be inserted at the exact location where the required features are present, then the surfaces are cut to generate a curve: 

3D curves on a 3D scan

The curve can then be exported as a STEP file into Autodesk Inventor:

2D curve from 3D scan

Now the reverse engineering can begin:

Internal and External Diameters can be accurately found and double checked to the physical part.

2D design from 3D scan

The most intact tooth was used to replicate:

2D draw gear teeth

Then the tooth was patterned to have the exact number of teeth as the original:

Extrude 3D object

A few more details completed then the final 3D model is complete:

3D Design of gear complete


And then CNC machined at Cammthane:

Scan to machined complete

Completed by Gavin Biggs - Cammpro Engineer 21/06/2021


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