Micrometer Stand

Materials: 17-4 & 303 Stainless Steel, Hardware

Processes: 3D Scanning, Metal 3D Printing, 3D Scan Data Processing, Composite 3D Printing, Turning

Tools: Faro 3D Scanning Arm, Polyworks Scanning Software, Meshmixer Software, Meshlab Software, Solidworks, Fusion 360, Markforged Mark 2, Markforged Metal X System, Haas SL10

About: The goal of this project was to learn the workflow from scanning objects to 3D printing. While this might seem fairly straightforward, there were quite a few pitfalls that I ran into along the way. I chose to scan and print a copy of the Mitutoyo Micrometer Stand as it fit the build volume of the metal 3D printer I had access to and would provide a useful initial test.

Scanning: I scanned the three components separately using the Faro arm within the Polyworks software. With about an hour of instruction, I was able to get some extremely detailed point clouds of the objects. I merged multiple scans into one object within the software, allowing me to get several sides of the objects into one STL file. In retrospect, I would have spent more time getting a 100% complete and watertight scan in the first place.

Modeling: Here is where the hard part started. Once you have the STL from scanning, you almost always need to fix it. This entails filling gaps, removing errant polygons, smoothing certain sections and finally decimating the model. The biggest letdown of my workflow was the process of translating STL files, with massive numbers of polygons, to sketch-based design software (Solidworks / Fusion 360) as they do not operate well with huge polygon counts. This required the aforementioned decimation where the software removes polygons and creates larger faceting. I used Meshmixer primarily for fixing the STLs and Meshlab for decimation. Once decimated, I was able to bring the files into Fusion 360 and apply more precise surfaces like the interface of the threaded fasteners and the base. I also added small holes on the base to accept rubber feet.

I found that it was easier to model the two smaller clamp parts from scratch, using the scan as reference only. Some voids and pockets in the model made it difficult to fix, and the geometry was simple enough to model quickly. 

Printing: The original stand, as manufactured by Mitutoyo, has a shelled out core to save on material and weight during casting. I found that trying to print a part, in its normal orientation with this shell, consumed more material, took longer, and was more prone to failure. Because the Markforged Metal X system can print internal infill structures, unlike DMLS, modeling and printing this with a flat base was much more efficient. This is a great example of a design for manufacture change between casting and 3D printing. 

Machining: I turned the required hardware out of 303 and permanently Loctited them to some off-the-shelf knobs. 

Conclusion: In the future, I would use scans only as reference material from which to model parts that require precision features. STL files from scans have far too many polygons to import into 3D modeling software like Solidworks or Fusion 360. In this case the result was visible faceting on the final product.

© 2020 Parker Musselman