Hacker News Reader

Sometimes such a plastic parts sole function is to break to avoid major damage to the rest of the machine. If you make it stronger and the same conditions occur something else might break or bend that is a lot harder to replace or repair.

You'll see the same in farming equipment, there are usually one or two sacrificial bolts in there that will be happy to snap if the tool gets wedged, rather than that the tool snaps.

View on HN

I get the sacrificial analogy, but in fact, the larger problem is IF the cam does fail, will it allow interference that will lock up at speed and potentially destroy the highly powered but delicate mechanisms, as you find destroys engine valvetrains, mainframe printers, among others. And this is what it did; when it failed everything locked, but luckily nothing was destroyed because otherwise built like a tank. The alternate explanation is that it is simply a very complicated cam device with many extreme contours, expensive to fabricate from anything but plastic injection, with high force followers that cause it to fail over time, leading to a trip to the sewing machine repairman. edit: I called it a pulley, but it in fact was a complicated cam.

Reply on news.ycombinator.com