Reverse engineering classic cars means rebuilding a part from the part itself when the drawings, tooling, or supply behind it are gone. The restorer holds an original, or what is left of one, and the goal is a model detailed enough to make a new part that fits. This guide covers when a part is worth the effort, what to decide before anything is made, and how the replacement is made and checked.
The work has three steps: capturing the surviving part, rebuilding it as an editable CAD (computer-aided design) model, and making a new part from that model. The capture can be a 3D scan, and the rebuild is where an engineer decides which features carry dimensions and which are only wear. Our guide to the 3D scan to CAD workflow covers those first two steps in detail, so this post stays with the decisions around them. Kemperle does the scanning, CAD work, and making in one place.
When Is Reverse Engineering Classic Cars Worth the Effort?
A part is worth reverse engineering when it cannot be bought, or when the one that can be bought does not fit. Even a car maker meets this problem. The Porsche Classic range includes some 52,000 parts, and a part running low is reproduced with the original tools. For parts needed in very small numbers, Porsche said in 2018 that producing small batches with new tools would be largely inefficient.
Its answer for the clutch release lever of the 959, of which only 292 cars were built, was to print the lever in steel by selective laser melting. Mercedes-Benz Classic took the same route for parts such as the inside mirror base of the 300 SL Coupé, and said printing suits smaller quantities and cases where the genuine tools no longer exist. A restorer with one cracked housing faces the same arithmetic on a smaller scale. Tooling for a single part is hard to justify, while a model and one printed or routed part can fit the job. Porsche adds that three-dimensional design data or a 3D scan is a sufficient basis to begin production, and that producing on demand removes tool and storage costs.
Should the New Part Copy the Old One or Improve It?
Copy what has to match and decide the rest on purpose. Mounting points, hole positions, and mating surfaces have to match the car, while wear, dents, and casting flaws on the original do not need to be reproduced. Where the original failed, the model is the place to fix it. Mercedes-Benz Classic made its printed 300 SL Coupé mirror base 42.5 millimeters longer than the original, so the mirror sits a little higher and gives a better view to the rear. Its printed spark plug holder grips the plug with a magnet instead of a female connector, which lets one holder suit every plug type.
The original controller handles for Barcade were thin-walled ABS (acrylonitrile butadiene styrene) parts that were no longer available. We scanned the samples, modeled everything in CAD, and redesigned the internal ribs, which also reinforced known weak spots in the originals, and the new handles still match the originals visually. We would ask what a part has to do before deciding what to correct, because a fix that helps a working part can count against it on a period-correct restoration. Where a part has to follow a worn body panel, the choice between matching the car as it is and restoring its original shape is covered in our guide to classic car 3D scanning.
Which Process Makes the Replacement?
The part’s material, size, and quantity decide. We 3D print, CNC (computer numerical control) route plastics, wood, and soft metals, and make molds and castings. A single part is a candidate for printing or routing, since neither needs a mold, and several identical parts can justify a mold and casting made from the same model.
Material comes first, because the part has to survive where it sits. Porsche notes that, depending on the application, its plastic parts must resist oils, fuels, acids, and light, and we would apply the same check to any replacement, because a wrong material fails where the part sits. A load-carrying part is a different case. Porsche proved its printed steel lever with a pressure test at almost three tonnes and a tomographic examination for internal faults before driving it in a test vehicle. We would want proof of that kind for any part in a load path, because a failure there costs far more than a misfit does.
Will the New Part Fit the Car?
Yes, if it is checked in two stages: digitally against the scan, then physically before the final material is committed. Porsche says it confirms size and fit by testing with the part installed. Barcade’s handles show the value: printed prototypes went onto a cabinet already in service, and molds were committed only after ergonomics and internal fit checked out.
A fit problem found on a printed test piece is fixed in the file, while the same problem found on a finished casting means a new mold. We would also check the final part against the model, because the same fault found late costs a new mold. Bring the neighboring parts to the test fit when you can, because a part can match its own scan and still foul the piece beside it.
Which Details Help Us Start?
Bring the part, even if it is broken, along with the car’s make and year and where the part mounts. Photos of the parts it meets help, and so does a note of what failed on the original. Tell us about any measurement you already trust, such as a bolt spacing or a shaft diameter, because it gives the model something to be checked against. Knowing how the part will be made is not required, because choosing the process is part of the work.
Our reverse engineering service covers the path from scan to finished part, and our overview of reverse engineering in manufacturing shows how the same method applies beyond cars. To start, use the contact form or call 718-557-9578.
Sources: Porsche Newsroom, Porsche Classic supplies classic parts from a 3D printer; Mercedes-Benz, Future meets Classic press release of 22 November 2018, as published by Automotive World.
