Minor mechanical mystery

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Jennifer
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Joined: 28 Apr 2010, 14:03

Minor mechanical mystery

Post by Jennifer »

In a thrift store a few weeks ago I bought an old jewelry box which I use to hold and organize paper clips and similarly tiny items I keep on my work desk. It's the kind with a wind-up music mechanism in it, and if everything worked properly then, assuming the musical mechanism was fully wound, every time I opened the lid of the jewelry box, the music would play until either I closed the lid again, or the musical mechanism wound down.

In some music boxes, especially the better-quality ones, the compartment holding the mechanism is behind glass (or at least clear plastic), attached with screws, so you can actually see it as it works, and with a jeweler's screwdriver you could remove the panel to repair or replace the music mechanism if necessary. But my jewelry/office-supply box was of much cheaper manufacture; the music-box compartment is made of the same material as the rest of the jewelry box, and its panels are attached with glue rather than screws. So I can't see the actual music mechanism in my box, but I'm almost certain it's a rotating-cylinder kind, like this:

Image

I understand the basic principle of how these work: the cylinder is covered with little raised bumps. As it rotates, the bumps push down or flip up various flimsy metal strips, each strip corresponding to a different music note. Thus, the pattern of bumps determines which tune the music box plays. In the picture I posted, you would turn that tiny handle to make the cylinder move and play music. But in wind-up music boxes, there would be a tiny coiled spring instead. When you wind up the music box, the spring coils tighter, which "stores" energy, then when it plays back, there's a series of gears and sprockets and stuff controlling the rate at which that coiled spring relaxes, releasing the wound-up energy to turn the cylinder and play the music.

So I understand these basic principles (though I have no idea how, specifically, those "gears and sprockets and stuff" are arranged to make the stored energy in the coiled spring turn that cylinder). And I understand SOME ways this music mechanism could break down: if the coiled spring broke at any point; if any of those other moving parts were to break; if the metal strips were too stiff or heavy for the cylinder-bump to nudge them out of the way; if dirt or other stuff got into the gears and clogged them up ... if any of these, then nothing will move (or at least, the chain-reaction movement will break down somewhere between the spring and the cylinder, which will not rotate) and the music won't play.

So, regarding my repurposed desktop supply box, I would understand if its music mechanism were broken enough to not play at all. But mine is broken in a different way: when I first found it, and opened the lid to inspect the inner compartments, the music began to play as soon as I opened the lid, and the tinkly notes played during the whole inspection. So I thought the music mechanism was in working condition. Not that it matters for my purposes -- I'd actually prefer NOT to hear tinkly music every time I use certain types of commonplace items at my desk, so even if the music mechanism were in perfect working condition, my plan was "listen to it just long enough to hopefully identify the tune, then let it wind down completely, and not re-wind it again."

When I brought the box home and opened its lid, the music mechanism only played six or seven notes before it stopped. This wasn't enough for me to name that tune, so I wound up the mechanism again -- or tried to. Turns out I couldn't give the wind-up lever even one full turn before it got stuck, and when I opened the box lid again, I again heard only a few tinkly notes before it stopped.

So I figured fine, it's broken somehow, I'll treat this as an ordinary non-music box ... except it still plays music sometimes. Not every time or even MOST times I raise the lid, though -- given the type of stuff the box holds, normally I'd only open its lid to retrieve something MAYBE once a day, or once every other day -- and maybe one time out of every three or four, the box will play anywhere from two to six tinkly notes before stopping. (Except for when I made the experiment of deliberately opening and closing the lid multiple times in a row: it never made a sound. But it did when I opened the box next day to retrieve my nail clippers.)

As of right now it hasn't played any music notes since IIRC yesterday afternoon, and I don't know if it truly is silenced for good (unless I try winding it again), or if it's going to play a few more notes in the near future. But either way, I'm trying to figure out -- assuming this is a spring-powered turning-cylinder music box, what could be wrong with its workings, for it to have this specific problem of "It WILL play music, but only a handful of notes at a time, then you must wait anywhere from several hours to a whole day before it'll play a handful of notes again"?

I understand "it plays, and winds and unwinds, normally," I'd understand "It won't play, wind or unwind at all," but I don't understand how this hybrid problem "It plays or it doesn't, but only a few notes at a time" can be a thing. Or how, if/when I tried to wind up the mechanism, I can only turn it what was clearly a tiny fraction of "the full way," assuming a properly working mechanism.
"Myself, despite what they say about libertarians, I think we're actually allowed to pursue options beyond futility or sucking the dicks of the powerful." -- Eric the .5b

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Jennifer
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Re: Minor mechanical mystery

Post by Jennifer »

Just opened the box, and it played two musical notes and then stopped. First time in at least 36 hours / 7 or 8 lid-openings.
"Myself, despite what they say about libertarians, I think we're actually allowed to pursue options beyond futility or sucking the dicks of the powerful." -- Eric the .5b

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Highway
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Re: Minor mechanical mystery

Post by Highway »

I'm going to guess that the spring is severely overwound, that's why you can only wind it a partial turn before it stops, and that there is some other problem in the mechanism that prevents it from playing. It is probably something similar to this one's problem, all gummed up. A couple notes play at a time because that's all the drum is turning in that time period. The other possible problem is that the stopping mechanism is messed up and not disengaging properly.

But I would bet that the spring is way overwound.
"Sharks do not go around challenging people to games of chance like dojo breakers."

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Jennifer
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Re: Minor mechanical mystery

Post by Jennifer »

Seventeen consecutive musical notes when I opened the box today. Definitely a record, for my ownership of it.
"Myself, despite what they say about libertarians, I think we're actually allowed to pursue options beyond futility or sucking the dicks of the powerful." -- Eric the .5b

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Jennifer
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Re: Minor mechanical mystery

Post by Jennifer »

Went two whole days without any music (after some minor re-arrangements of my workspace, I'm opening the box more frequently now, an average of 3 - 5 times per day), but once again, as soon as I figured "It is finished, no more music" it went through an unusually prolific period, playing music as often as once every three openings, for two to 10+ notes at a time.

But there's a slight change in how/when the music plays: originally, if the music DID play it would be as soon as I opened the box. But the past couple times now, the box stays silent when I open it, then some notes started to play after I started to lower the box lid. IOW, whatever's spurring the mechanism to occasionally move, it's now doing this as the box lid is going down rather than up.

Oooo, I wish this mechanism were in a transparent compartment so I could actually SEE what is and isn't going on.

I am also wondering -- speaking as someone who does know music boxes, clocks and other spring-powered mechanical devices can be "overwound," which I gather has something to do with "coiling that spring SO tightly, it can't release the energy again for some reason" ... but now I'm wondering if an overwound spring can eventually ... I dunno ... relax itself back into normalcy again, if left to its own devices? Presumably, every time the box DOES play a few music notes, it's because that spring is uncoiling just a weensy bit more.

I have not so much as touched the wind-up key on the box's underside since my first unsuccessful attempt to wind it. But now I'm thinking of a new long-term experiment: after I go a whole week of normal box-opening without hearing any music, try very carefully to wind up the music box again and see if it works better this time.

... ha, just opened the box for experimental reasons, and heard three more notes, this time as I opened the lid.
"Myself, despite what they say about libertarians, I think we're actually allowed to pursue options beyond futility or sucking the dicks of the powerful." -- Eric the .5b

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Jennifer
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Re: Minor mechanical mystery

Post by Jennifer »

Heh heh. I never mentioned the box to Jeff, and he did not notice it the last time he sat at my desk to do some computer upgrades for me, but today I went into my office to retrieve something while he stood chatting in the doorway, and when I opened the box the music started to play and he gave me an incredulous "WTF is THAT?" look until I explained where the music came from.

The music also played again when I opened the box for a different reason an hour later. I think it plays more frequently now than it did when I first got it.

ETA: And four more notes when I opened the box just now. This thing is on a roll.
"Myself, despite what they say about libertarians, I think we're actually allowed to pursue options beyond futility or sucking the dicks of the powerful." -- Eric the .5b

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