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Just curious, maybe it's a stupid question but i'd like to know why the following happens: Even though a hdd platter is extremely well balanced/aligned, it still buzzes and vibrates when spinning. A hdd platter must be produced with an almost zero tolerance, it's almost perfectly round and flat so the center of gravity is almost exactly at the center, where the axis of the platter is. And the spindle motor is brushless. So you shouldn't be able to feel any vibrations when you hold or touch an hdd. And i'm not talking about when it's busy reading or writing, you can still feel it when it's not handling read/write requests.

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    Almost zero tolerances? Maybe, maybe not. But not zero. The spindle is not exactly perpendicular to the disk surface; the weight of the platters is not perfectly distributed, etc. Some of the energy becomes heat, some becomes noise, some becomes vibrations.
    – user115145
    Jun 24, 2014 at 21:26
  • I also think that because the spindle isn't secured to the top of the disk that you get some amplification of any rotational impurities. If the spindle were attached to the top of the case there would be less x and y axis movement, thus reducing vibration
    – Kinnectus
    Jun 24, 2014 at 21:34
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    It's an interesting question, but I'm not sure if it fits here. Physics.SE may be a better place to ask it, you may want to flag it for migration (use the needs moderator attention option).
    – gronostaj
    Jun 24, 2014 at 21:38
  • Try physics.stackexchange.com
    – LawrenceC
    Jun 24, 2014 at 21:39

2 Answers 2

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If a disk is spinning at a constant rate, and there wouldn't be any other moving parts in it, then it won't vibrate much. But "perfect" balance doesn't exist, there's ALWAYS a little unbalance, how tiny it may be. Disks slow down and speed up, and it's this acceleration and deceleration that cause disks to vibrate as well. There's also the fact that your reading/writing heads are moving at very fast speeds. Every time they move around to read different areas of the disk, they will cause a slight vibration.

It's all simple physics and understanding that "perfect" does not exist in the real world, only in the theoretical world. The heavier the components of moving objects, the more difficult it is to hide the vibration through its movements. And a disk has a lot of moving parts, some of them are quite heavy.

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The reason why a harddisk vibrates is simply science, called centrifugal force.

The disks spin so fast that it wants to pull outwards in all directions, and eventually it will slightly vibrate. Because of good construction, the harddisk plates are not moving. Given that the forces are really high, the entire harddrive starts to vibrate.

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  • "it wants to pull outwards in all directions" - then the vector sum of all forces is zero, so why would it vibrate?
    – gronostaj
    Jun 24, 2014 at 21:37
  • Have you ever seen the science experiment with a wheel connected to a wire, that if you spin the wheel very fast it'll lift? That same force (called centrifugal force) is what causes the harddisk to vibrate.
    – LPChip
    Jun 24, 2014 at 21:47
  • I find your answer vague and imprecise. First you mention centrifugal force, then "pulling outwards in all directions" (which is what I referred to in my prevous comment). If the hard drive construction is in fact good, then centrifugal force should be a constant upward force balanced out by some other force, so zero in total.
    – gronostaj
    Jun 24, 2014 at 22:04
  • I'm sorry. Science is not my strong suit, so I don't know all the terminology.
    – LPChip
    Jun 25, 2014 at 10:28
  • It's not the terminology that is a problem here (and we both got it wrong, because centrifugal force isn't perpendicular to the platter). It's Newton's 1st law of motion that makes this question interesting, because if the platter is perfectly round and the axis doesn't move, then all forces should be balanced and the drive shouldn't move, yet it still vibrates.
    – gronostaj
    Jun 25, 2014 at 10:51

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