[TheForge] Off-topic: Anyone have experience with dynamic balancing, vibration sensing & vib-synched stroboscopes, and/or critical disk and/or rotor speeds?

[Peter Fels & Phoebe Palmer]

Use a fatter shaft to avoid some of the dynamic consequences?

Bruce Freeman wrote:
> Walt,
> That's static balancing.  I'll be doing something like that, but it
> won't suffice for higher speeds.
> 
> On Wed, Jul 15, 2009 at 10:55 AM, <wmullett at bright.net> wrote:
>> Bruce,
>>
>> You don't say how large this is and if you can take it apart or not.  I know nothing about dynamic balancing but could you use any of the following:
>>
>> Forty years ago I was into slot car racing - not the home variety.  We used to take brand new motors, cut the windings out and re-wind them with a different wire.  When done, we would balance the armature using epoxy.  Not in place but we placed the armature straddle across two razor blades so that there was no friction.
>>
>> I would think similar principles could be applied to larger items.
>>
>> Walt
>>
>> ---- Original message ----
>>> Date: Tue, 14 Jul 2009 22:21:05 -0400
>>> From: theforge-bounces at mailman.qth.net (on behalf of Bruce Freeman <freemab222 at gmail.com>)
>>> Subject: [TheForge] Off-topic: Anyone have experience with dynamic balancing, vibration        sensing & vib-synched stroboscopes, and/or critical disk and/or rotor speeds?
>>> To: Blacksmithing List Sponsored by ABANA <theforge at mailman.qth.net>
>>>
>>> I'm working on a mechanism that involves a high-speed rotor, and I'm
>>> to the point where I really need to dynamically balance the thing.
>>> I've run it at about 1740 RPM and maybe as high as twice that.  (I
>>> haven't measured the pulleys.)  I get more vibration than I want, but
>>> it's not flying apart or anything scary.  (I'm aiming for an arbitrary
>>> 10kRPM.)
>>>
>>> So, I've spent the day reading up on dynamic balancing and have
>>> learned a fair amount, but nothing I can put to immediate use.  I have
>>> learned that above the (first) critical speed (i.e., the speed
>>> equivalent to the fundamental vibration frequency of the rotor), the
>>> vibrational behavior changes and it is possible to automatically
>>> balance the device.  There are patented mechanisms that utilize this
>>> phenomenon.  However, I have no idea whether I have yet approached the
>>> critical speed for this rotor, and trying to calculate that speed
>>> (which is possible, in principle) would be rather difficult due to the
>>> odd construction of the rotor.  Furthermore, I'm not at all sure I
>>> want to take it up to the critical speed without first dynamically
>>> balancing it.
>>>
>>> The best alternative I've come across so far is to utilize some sort
>>> of sensor that will register vibrational period and amplitude and,
>>> preferably, trigger a stroboscope so that one can visualize where the
>>> excess weight is on the rotor.  Unfortunately, I'm quite unclear about
>>> what sort of sensor this requires.  I actually have a stroboscope, and
>>> can easily "stop" the motion of the rotor with it, but it is triggered
>>> by time, not by an external sensor, and correlating the flash to the
>>> vibration is beyond my abilities for the nonce.
>>>
>>> Furthermore, I read that in dynamic balancing, it may be necessary to
>>> have a support structure with "soft" bearings.
>>>
>>> As anyone knowledgeable in the field can tell, I'm in over my head
>>> here.  I would appreciate any pointers, assistance, words of wisdom,
>>> URL's or whatever that you can provide.
>>>
>>> --
>>> Bruce
>>> NJ
>>>
>>> The total lack of evidence is the surest sign that the conspiracy is working.
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