Poor Engineering or Planned Obsolesce?
Wife's 10+ year old sewing machine went BANG! while she was using it yesterday. Out comes the tools - and today she has a brand new one. Seems somehow the gear that drives the shuttle jumped a tooth, and bound itself up. Try as I might I couldn't get it to run freely, let alone back in time.
So, it became a "parts source', as I tend to tear everything apart for usable parts. While doing so I noticed that all the continuously moving parts were predominately metal, and plastic was used in the housing and many of the "movable parts" that have a low duty cycle - the manual knobs that control the settings, etc.
All except that one gear - it's plastic, and rotates forward and then back once for each needle stroke, so it's a busy little gear. There is another drive gear in the top - a spiral worm gear, made of metal. Doesn't even look worn. So, was the plastic gear used in the shuttle drive designed to fail, or just a botched engineering design?
1st pic - failed gear
2nd -overall view - note the nice cast aluminum frame
3rd - metal worm gear - rotates once per cycle
Not really woodworking related, except I notice the same type of engineering in many of the power tools I dissect.
Alexis de Tocqueville was a very smart man.