Moving from a broken part to a 3D printed replacement can be more complicated than you think. Fortunately, Xometry has the right resources to do this job. This story is about reverse engineering, how 3D printing can be used for parts and what it takes to generate 3D CAD from complex physical parts. If you’ve ever had something you wanted to replicate with a 3D printer, or wanted to learn more about 3D scanning and engineering, read on!
I have a part, can you 3D print a replacement part?
In late June, the Xometry team received a message from Linda Wagar, a consumer reporter for Fox4 News in Kansas City. Wagar produced a section called Problem Solvers and directed a story about a retired farmer who bought an expensive massage chair only to break it in less than a year. Farmer Rick Davison found out that the company he bought the chair from was no longer in business. Davison even went to a local store to try and get a repair, to no avail. Wagar put on her detective hat and began her investigation. After her first post about the unresponsive company and workshop aired, she wasn’t finished. 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 racks that were critical to the massage chair’s function. 3D printing has the amazing ability to produce production parts for the end user in small quantities and at low cost. The prerequisite for this, however, is one thing: 3D CAD. This is the three-dimensional data that is interpreted by the printer to create the shape of the part. In other words, no CAD, no printing. The broken rack, the identical intact rack, and a plastic washer were delivered to Xometry and it was time to determine how the obtained parts could be used to create 3D models – this is known as reverse engineering. Xometry received the parts and went to work creating a 3D printable model for manufacturing.
Reverse engineering challenges
Reverse engineering can be approached in many different ways. Often the easiest way is to use measurement tools to fully reproduce the design from scratch in CAD. This is ideal for parts that are simple and have geometrical features that are easy to measure.
The washer, for which Davison requested some extras, can easily be regenerated in CAD. In a few minutes, this part was measured, duplicated in CAD (SOLIDWORKS) and uploaded to Xometry’s Instant Quoting Engine℠ for production.
But what about the rack? This shape was not intuitive, curved like a wedge with protruding protruding features on the opposite side of the gears. The part is also a long piece of plastic, which means that it can show slight warps or deformations even when it is not clamped. Put simply, vernier calipers and handheld measurements would be too risky to create a functional design. It was time to take on the big guns and work with some professionals – Xometry named the Maryland-based 3D scanning experts at Direct Dimensions.
In a video call, Direct Dimensions CEO Michael Raphael and his team were able to inspect the curved part and determine that a laser line scanner on an articulated arm would be the best approach. So we arranged an on-site visit to their location for a 3D scan.
Fortunately, the intact version of the defective part was available for scanning. Having a “good” version of a part to replicate removes some of the assumptions that can arise when trying to reverse engineer a broken, cracked, warped, or incomplete part.
Here’s how to prepare a part to scan
At Direct Dimensions, the intact part was placed on pillars to obtain scan samples of each face and feature. After the setup was done, it was time to “make up” the part. Outside of the industry, few know that high fidelity scans often require surface preparation to get accurate surface readings. If a part is shiny, translucent, or not dry, there may be incorrect or missing data during the scanning process. Imagine a projector screen catches the light much better than a pane of glass.
In this case, the rack had residual oil in its teeth that needed to be scrubbed off. We used some dish soap and a toothbrush to get into the grooves and blasted the part dry. The glossy translucent surface was then evenly sprayed with a special temporary coating to give it an opaque matt finish. The coating used creates a white matt surface with minimal thickness. This surface preparation ensures that the scan will provide the best data when using 3D scanning processes with visual light.
Now the part was ready to be scanned. The process used a FARO Quantum ScanArm, a laser scanner on the end of a calibrated articulated arm. The scanner uses visible light to collect data from the surface of the part and transmit it to the software.
This process typically takes time and involves a lot of scanning, stopping, checking, and going back if surface features around the part are missing. This process allows you to see the collected data in real time for quick review.
Once Xometry had the scan data, the reverse engineering process wasn’t quite complete. The scan data provides exact data points of the physical model, but is not complete. On the one hand, the scan data show residual features of the holder that was used to hold the massage chair part – these must be removed digitally. There are also holes and gaps in the mesh surface; Even the best scanners do not immediately create a fully manufacturable model. For 3D printing, mesh data must be considered “watertight,” which means that all part features have an uninterrupted exterior surface. After all, the original part scanned is a long plastic part, which means that the original part design may have experienced a slight warp on flat surfaces during its manufacture or lifetime. All of these considerations must be verified by a trained reverse engineering draftsman.
The Direct Dimensions team used the raw data set from the scan as a starting point for reverse engineering and developing a manufacturable CAD of the part. Within a day, they were able to provide a high quality STEP file with parametric data for 3D printing.
Xometry structure of the parts
The parts were ready to be manufactured with the design file uploaded to Xometry’s Instant Quoting Engine℠. Given the length of the part, the details required, and the durability required, Xometry engineers decided that FDM Ultem 9085 was an ideal material. FDM, or Fused Deposition Modeling, can 3D print up to 3 feet using engineering plastics for end-use parts. Xometry 3D printed a set of the racks overnight from the light brown Ultem material. Ultem is incredibly tough and wear-resistant – an ideal material for continuous use of a rack without the need for more expensive processes like CNC machining or plastic injection molding. The replacement discs were printed in durable laser-sintered nylon 12.
The moment of truth: fulfilling a farmer’s vision for lying down
The replacement parts and their originals were returned to Missouri, and it was time for the moment of truth. Would the 3D-scanned, reverse-engineered and 3D-printed spare parts be correctly built into the frame of the chair? Remember, the Xometry team only had the parts and no matching parts for fit testing or pre-shipping inspection. Xometry relied on their experience and teams of experts to offer a first class product.
The ultimate test of success is that the reverse engineered and 3D printed design installs with ease. As part of a FOX4KC segment, Wagar took the parts to Davison’s house where they were installed live while the Xometry team watched a video call. After an hour of unpacking and assembling, Davison found the parts fit perfectly. The frames matched the contoured metal frame of the chair, and a gear system slid over the rails without a tie. For our engineers, it was a relief to see that everything went well, especially since Davion was back in his chair for the first time in months.
With the help of bespoke 3D printing and design services from Xometry and Linda Wager from FOX4, Rick Davison had his chair back in order! To learn more, read Linda Wagar’s FOX4 report, “After the manufacturer gives up, another company steps in to fix the Missouri men’s chair.”
From consumer goods to aerospace parts, Xometry can manufacture on-demand. Xometry’s Instant Quoting Engine℠ uses 3D files to instantly price various manufacturing technologies such as 3D printing, machining, molding, sheet metal, and more. With the new Suppliers Marketplace platform, users can connect directly to reverse engineering services, refinement services, manufacturers and much more. Xometry’s quality guarantee covers all work produced, and experienced manufacturers in our supplier network ensure compliance.
A very special thank you goes to Aaron Lichtig for his internal support on this project and the entire Direct Dimensions team that did excellent reverse engineering: Michael Raphael, Harry Abramson, Jeff Mechlinski, John Kelbel and Elaine Scott.