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From 3D Scanning to 3D Printing: A Behind-the-Scenes Look at Reverse Engineering

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Getting from a broken part to a 3D printed replacement can be more involved than one realizes. Luckily, Xometry has the right resources on hand to do the job. This story is about reverse engineering, how 3D printing can be used for replacement parts, and what it takes to generate 3D CAD from complex physical parts. If you ever had something you wanted to replicate with a 3D printer or wanted to know more about 3D scanning and engineering, read on!

I Have a Part, Can You 3D Print a Replacement?

In late June, the team at Xometry received a message from Linda Wagar, a consumer reporter with Fox4 News in Kansas City. Wagar produced a segment called Problem Solvers and did a story about a retired farmer who purchased an expensive massage chair only to have it break in less than a year. The farmer, Rick Davison, found out the company he purchased the chair from was no longer in business. Davison even went out to a local shop to try to get a repair with no luck. Wagar put on her sleuthing hat and started her investigation. After her first segment aired about the unresponsive company and repair shop, she wasn’t done. Davison still had a broken chair and Wagar was determined to find a solution.

Wagar reached out to Xometry to see if it could use its plastic 3D printing service to replace one of two curved gear racks that were critical to the function of the massage chair. 3D printing has the amazing ability to create end-use production parts in low quantities and at a low cost. However, it does require one thing: 3D CAD. This is the 3-dimensional data that is interpreted by the printer to create the shape of the part. In other words, no CAD, no print. The broken gear rack, the identical intact gear rack, and a plastic washer were shipped to Xometry and it was time to determine how to create 3D models from the parts received–this is called reverse engineering. Xometry received the parts and got to work to make a 3D printable model for manufacturing.

The parts received by Xometry.

Reverse Engineering Challenges

Reverse engineering can be approached in many different ways. Often the simplest way is to use measuring tools to fully reproduce the design in CAD from scratch. This is great for parts that are simple and have easily measured geometric features.

The washer, which Davison requested a couple of extras, is easy enough to re-generate in CAD. In a matter of minutes that part was measured, duplicated in CAD (SOLIDWORKS), and uploaded to Xometry’s Instant Quoting Engine for production.

Simple geometries like this washer can be reverse-engineered with calipers and drafted in CAD in minutes.

But what about the gear rack? That shape was non-intuitive, curving as a spline, with protruding boss features on the opposite side of the gears. The part is also a long plastic piece, meaning that it may already have slight warp or distortion in an unconstrained state. Simply put, calipers and hand measuring would be too risky to create a functional design. It was time to bring in the big guns and work with some professionals–Xometry called the Maryland-based 3D scanning experts at Direct Dimensions.

 

Over a video call, Michael Raphael, CEO of Direct Dimensions, and his team were able to review the curved part and determine that a laser line scanner on an articulating arm would be the best approach. So we arranged an on-site visit to their location to get a 3D scan.

Luckily, the intact version of the broken part was available to scan. Having a “good” version of a part to replicate removes some of the assumptions that may occur when attempting to reverse engineer from a broken, cracked, warped, or incomplete part.

Getting ready for 3D scanning to intact gear rack.

 

How to Prepare a Part for Scanning

At Direct Dimensions, the intact part was set up on pillars to get scan samples of every face and feature. Once the setup was ready, it was time for the “makeup” on the part. Outside of the industry, few know that high-fidelity scans often require surface preparation in order to get accurate surface readings. If a part is shiny, translucent, or not dry, there may be bad or missing data during the scanning process. Think of how a projector screen captures light much better than a glass pane.

In this case, the gear rack had residual oil in the teeth that needed to be scrubbed away. We used some dish soap and a toothbrush to get into the grooves and air blasted the part until dry. Then, the shiny translucent surface was evenly sprayed with a special temporary coating to bring it to an opaque matte finish. The coating used creates a white matte surface while adding minimal thickness. This surface preparation assures the scan will give the best data when using 3D visual light scanning processes.

Before scanning, the part had to be cleaned of oil and treated with a special matte coating.

Now the part was ready for scanning. The process used a FARO Quantum ScanArm, which is a laser scanner on the end of a calibrated articulating arm. The scanner used visible light to collect data of the part’s surface and transfer that to software.

Capturing surface data using 3D scanning

This process typically takes some time, involving a lot of scanning, stopping, reviewing, and going back if there are missing surface features around the part. This process allows you to see the data being collected in real-time for rapid review.

Scan capture data as it is read by a FARO laser scanner

Once Xometry had the scan data, the reverse engineering process wasn’t quite done yet. The scan data gives accurate data points of the physical model, but it is not complete. For one, the scan data has remnant features of the fixture used to hold the massage chair part—these need to be digitally removed. There are also holes and gaps in the mesh surface; even the best scanners do not create a fully manufacturable model on the first go-around. For 3D printing, mesh data must be considered “watertight,” meaning that there is an unbroken outer surface across all part features. Lastly, the original scanned piece is a long plastic part, meaning that the original part design may have experienced subtle warping on flat surfaces from its manufacturing or service life. All of these considerations must be reviewed by a trained drafter for reverse engineering.

The raw dataset from 3D scanning the part.

The Direct Dimensions team used the raw data set from scanning as a starting point to reverse engineer and develop manufacturable CAD of the part. Within a day, they were able to provide a high-quality STEP file with parametric data ready for 3D printing.

The final CAD file was reverse-engineered from the 3D Scan data.

Xometry Building the Parts

The parts were ready to be manufactured with the engineered file uploaded to Xometry’s Instant Quoting Engine℠. Because of the part’s length, the details required, and the need for longevity, Xometry engineers decided that FDM Ultem 9085 would be an ideal material. FDM, or fused deposition modeling, can 3D print up to 3 feet using engineered plastics for end-use parts. Xometry 3D printed a set of the gear racks out of the tan Ultem material overnight. Ultem is incredibly tough and wear-resistant—an ideal material for the continuous use of a gear rack without the need to use more expensive processes like CNC machining or plastic injection molding. The washer replacements were printed in durable laser sintered Nylon 12.

3D printed Ultem replacement gear racks were made overnight through Xometry.

The Moment of Truth: Fulfilling One Farmer’s Vision for Reclining

The replacement parts and their originals were shipped back to Missouri, and it was time for the moment of truth. Would the 3D scanned, reverse engineered, and 3D printed replacement parts install correctly into the chair’s framework? Keep in mind that the team at Xometry only had the parts and had no mating pieces for fit tests or checks before shipping. Xometry relied on its experience and its expert teams to provide a top-notch product.

The unboxing of the replacement parts and the original broken pieces.

 

The ultimate test of success is if the reversed engineered and 3D printed design would install without any troubles. As part of a FOX4KC segment, Wagar brought the parts to Davison’s home, where they were installed live while the Xometry team watched over a video call. After an hour of unpacking and assembly, Davison found that the parts fit perfectly. The racks mated to the contoured metal frame of the chair, and a geared system glided down the tracks without binding. For our engineers, it was a relief to see everything worked out, especially as Davion reclined in his chair for the first time in months.

The replacement part is installed and working! (Source: FOX4KC)

With the help of Xometry’s custom 3D printing and design services and FOX4’s Linda Wager, Rick Davison had his chair back in order! To read more, check out the FOX4 report by Linda Wagar: “After manufacturer abandons, another company steps in to fix Missouri man’s chair.”

About Xometry

From consumer products to aerospace parts, Xometry can manufacture on-demand. Xometry’s Instant Quoting Engine℠ uses 3D files to instantly price in various manufacturing technologies like 3D printing, machining, molding, sheet metal, and more. With the new Suppliers Marketplace platform, users can directly connect with reverse engineering services, finishing services, manufacturers, and much more. Xometry’s Quality Guarantee backs all manufactured work, and expert manufacturers across our Supplier Network provide fulfillment.

A very special thanks to Aaron Lichtig for his internal support with this project and the whole team at Direct Dimensions who provided terrific reverse engineering services: Michael Raphael, Harry Abramson, Jeff Mechlinski, John Kelbel, and Elaine Scott.

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