Pitching in with the other engineers, the company making your $20 vibrator skimped as much on production costs as possible to maximize profit. This means you'll get a cheapo plastic unable to handle repeated impacts from the metal weight that causes the vibration.
Saint: an aeronautical engineer not thinking about materials? For shame. If something's breaking and you don't want it to, change your design!
Funinthesun, there are some funky plastics out there now. The high-impact ones do their job just fine against metals
