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Design Snippet: A clever innovation turned out to be a century old

Ten years ago, PCV group received a challenge from one of our customers: design a small, inexpensive but reliable gearbox with a 500:1 gear ratio. The gearbox was meant to be part of a handheld beauty device, so it would be mass-produced and used by a consumer which means no regular maintenance or lubrication. This kind of challenge was well suited for Dries Nijsen, a creative mechanical engineer and co-founder of PCV Group.

It took two days to work out the concept: an eccentric shaft driving two connected gears: the largest rotates within a fixed internal gear hub which has four more teeth than its counterpart. The second gear is smaller and drives a collet with internal gear teeth. The collet is the output shaft, which rotates significantly slower than the input.

“I wrote a formula describing this gearbox to determine the gear ratio, which was not trivial” Nijsen says. “Later, when I consulted the ‘Dubbel Handbook of Mechanical Engineering’, I noticed a familiar formula. This type of gearbox had apparently been invented a hundred years ago.”

Two days after finishing the concept, the 3D-printed parts arrived. “It was printed on a 2:1 scale, since SLS printers at the time were not precise enough to make this part (which is less than 50 mm in diameter).” All in all, it took less than a work week from the start of the project to have a prototype ready.

Although the client was impressed with the speed and quality of the work, the project this gearbox was designed for never came off the ground. The prototype has been sitting unused on a shelf for a decade now, much like how the original gearbox has been hiding in the pages of the dubbel handbook for over a century. We would love to find a good application for this gearbox. If you think you have it, please let us know.

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