Poor Engineering or Planned Obsolesce? - Woodworking Talk - Woodworkers Forum
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post #1 of 29 Old 05-19-2014, 09:51 PM Thread Starter
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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.
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Alexis de Tocqueville was a very smart man.
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post #2 of 29 Old 05-19-2014, 10:03 PM
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those gears look like the ones in my garage door opener that prior to the first failure, should have been lubed. was there a lubrication schedule provided, or something the manufacture fails to inform us
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post #3 of 29 Old 05-19-2014, 11:30 PM
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To answer you question, it was both and/or neither.

The design functioned for a full 10 years according to your testimony. Most people don't hang on to a car that long these days. So the design was good. The manufacturing was also good for the same reason. So it was not designed to fail as you hint.

Now, unless a replacement part can be had, and installed, your only options are to give up sewing, or buy a new machine. So it was indeed "known" to have an issue when released for public consumption. Of course, just a drop of grease may have prolonged the life of the part. I have a very old table saw (made in the 80's) that works great as long as I take care to lube it properly twice a year. Should it ever break I already know that parts are no longer available to repair it, so I'll be buying a new one.

Could I claim it was a bad design after having worked for so many years? I guess maybe, but I'm pretty sure that even the most liberal court in the country would throw the case out.

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post #4 of 29 Old 05-20-2014, 07:07 AM
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I agree with Johnnie on just about everything.
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post #5 of 29 Old 05-20-2014, 07:22 AM
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If things were still built to last and designed for repair, it would be heaps harder for the politicians and corps to create economic growth. But when stuff is built for short life and disposal, we need factories to build the replacements and a garbage & landfill industry to accept the waste. Voila! Economic growth!
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post #6 of 29 Old 05-20-2014, 07:25 AM
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What I know about sewing machine parts I could put in my eye and still see clearly. I can't say it was designed to fail, but my best guess the metal on plastic gear was done to keep it quiet.






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post #7 of 29 Old 05-20-2014, 08:12 AM
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I think the plastic gear was designed to be the weak spot in case something jammed. I do not know why the designers chose this option over a shear pin. I have seen this in other machines.

I have been looking at milling machines. One of the models I looked at has a plastic drive gear. This is also designed to be a weak spot and so will strip before the metal gears in the event something happens.
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post #8 of 29 Old 05-20-2014, 09:51 AM
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I've seen that same situation in expensive bindery equipment. I assume it was also designed as a breakaway part to keep more expensive parts from being damaged in the event of a jam. I also take note that the nylon used in the gear is termed self lubricating so there is not such a pressing need for constant lubrication.
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post #9 of 29 Old 05-20-2014, 10:29 AM
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Quote:
Originally Posted by SteveEl View Post
If things were still built to last and designed for repair, it would be heaps harder for the politicians and corps to create economic growth. But when stuff is built for short life and disposal, we need factories to build the replacements and a garbage & landfill industry to accept the waste. Voila! Economic growth!
They would also be a lot more expensive to build and consequently the retail price would be a lot higher.

The consumer would not like that so some smart company would make a less expensive model that would sell so well the first compsny would go out of business.


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post #10 of 29 Old 05-20-2014, 10:50 AM
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Just noticed the same thing on a shredder that died the other day. Very strong metal gears everywhere except for one plastic one, which is the one that failed.
They want to sell more stuff.
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post #11 of 29 Old 05-20-2014, 06:21 PM
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For a ten year old machine it doesn't look too bad. I'm expecting machines made from now on to have 3D printed parts with a life span only a few days longer than the warranty they come with.
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post #12 of 29 Old 05-20-2014, 10:14 PM
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Nylon gears are common on industrial machines, they run quieter and are usually in a location where they are the weakest link and will strip before damage is done to other parts. Generally they can be easily replaced and there is a supply of spares on hand. As for grease that is a debate that has been going on for years.

Wise men speak because they have something to say; fools because they have to say something -Plato

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post #13 of 29 Old 05-21-2014, 08:26 AM
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Good shirts come with a spare button or two for when you inevitably lose one of the originals. Perhaps good tools should just come with a spare gear replacement for the original one they have designed to be the weal link and fail first.
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post #14 of 29 Old 05-21-2014, 08:30 AM
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Quote:
Originally Posted by 4DThinker View Post
Good shirts come with a spare button or two for when you inevitably lose one of the originals. Perhaps good tools should just come with a spare gear replacement for the original one they have designed to be the weal link and fail first.
That would defeat the purpose of planned failure repair/replacement.






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post #15 of 29 Old 05-21-2014, 10:11 AM
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Neither my wife or anyone I know does enough sewing anymore to wear a machine out, however I do remember my mother taking hers to be repaired at a shop that specialized in such work.

Wise men speak because they have something to say; fools because they have to say something -Plato

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post #16 of 29 Old 05-21-2014, 10:30 AM
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Did you try to source the part? I helped my wife repair an anique sewing machine she was using until my mother loaned her a more modern one; if parts are around for machines from the 50s you should be fine. As Frank mentions, this can be a feature rather than a fault.
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post #17 of 29 Old 05-21-2014, 12:43 PM Thread Starter
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Quote:
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Did you try to source the part? I helped my wife repair an anique sewing machine she was using until my mother loaned her a more modern one; if parts are around for machines from the 50s you should be fine. As Frank mentions, this can be a feature rather than a fault.
No, figured it was 10 years old, time for a new one. Wife picked out a Brother machine, $169, does way more than the old one. If it lasts 10 years, $17 a year isn't bad. The cost of the gear, if available, would probably pay for 2 years on the new one.

Besides, I harvested a plethora of parts from the old one. And you know the saying- happy wife, happy life. She was in the midst of making a dozen full size quilts, one due the recipient in a couple of weeks, and didn't want to wait.

Alexis de Tocqueville was a very smart man.
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post #18 of 29 Old 05-21-2014, 12:59 PM
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Quote:
Originally Posted by Alchymist View Post
No, figured it was 10 years old, time for a new one. Wife picked out a Brother machine, $169, does way more than the old one. If it lasts 10 years, $17 a year isn't bad. The cost of the gear, if available, would probably pay for 2 years on the new one.

Besides, I harvested a plethora of parts from the old one. And you know the saying- happy wife, happy life. She was in the midst of making a dozen full size quilts, one due the recipient in a couple of weeks, and didn't want to wait.
Ah, my wife has been using various hand me downs from my mom who buys sewing machines worth the sum of my woodworking equipment, so they're always worth repairing.

I did read that the jigsaw/scrollsaw was invented by a fellow attaching a sawblade to his wife's sewing machine, so if you do replace the gear you sould always use it for something like that.
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post #19 of 29 Old 05-21-2014, 01:59 PM
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Quote:
Originally Posted by Alchymist View Post
No, figured it was 10 years old, time for a new one. Wife picked out a Brother machine, $169, does way more than the old one. If it lasts 10 years, $17 a year isn't bad. The cost of the gear, if available, would probably pay for 2 years on the new one.

Besides, I harvested a plethora of parts from the old one. And you know the saying- happy wife, happy life. She was in the midst of making a dozen full size quilts, one due the recipient in a couple of weeks, and didn't want to wait.
Just don't look at the embroidery machines... we've been looking at a "combination" machine because my wife and I both sew and she wants to also do embroidery... cheap ones cost $1000.

I've been using the same sewing machine since I was 22 years old or so... sewing everything from halloween costumes to backpacks to scuba and climbing gear. Still going strong, though the heavier weight materials do break needles all the time.
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post #20 of 29 Old 05-24-2014, 08:17 PM
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In defense of us Engineers out there, for the consumer industry products out there, they are often forced into sub-optimal choices due to the accountants trying to keep a product at a certain price while maintaining a high enough profit margin. So, it's not the engineer's fault, usually. It's the accounting department.
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