[TheForge] Off-topic: ...dynamic balancing, vibration...

[Bob Willman]

	Depending upon the shape/size of the rotating part(s), it is
possible to achieve static balance using hardened pivots or the actual
bearings but it may not be dynamically balanced. If we assume 2 absolutely
identical flywheels mounted on a shaft and assume that each flywheel has a
heavy side but that each heavy side happens to be located 180 degrees apart
from each other it is possible for the 2 flywheels and shaft to balance in a
static condition but the assembly will never be in balance dynamically. The
longer the shaft the more difficult the problem becomes.

Good luck. 


Bob Willman
Bowling Green, Ohio
The Eagle's Anvil
WB8NQW

-----Original Message-----
From: theforge-bounces at mailman.qth.net
[mailto:theforge-bounces at mailman.qth.net] On Behalf Of Peter Fels & Phoebe
Palmer
Sent: Wednesday, July 15, 2009 2:18 PM
To: Blacksmithing List Sponsored by ABANA
Subject: Re: [TheForge] Off-topic: ...dynamic balancing, vibration...

The shade tree approach would be to suspend the shafted assembly between
2 sharp, hardened points in the centering holes on the shaft ends, in a
lathe. Then give it  some whirls and mark the bottom points when it stops
moving. Shave off metal opposite the marks and repeat till crazy and the
marks distribute randomly.
But i doubt that'll get you to 10,000 RPM.

Bruce Freeman wrote:
> Probably good advice, but no can do.  Where money is involved, I have 
> to take a first go myself.  Other folks told me to draw up my parts 
> and send them out to be made in a professional shop.  Had I done that 
> I would never have got as far on this project as I have.  The 
> turn-around delays alone would have done me in.  Not to mention the 
> lack of opportunity to see for myself which designs were easily 
> executed and which were bears.
> 
> On Wed, Jul 15, 2009 at 12:22 AM, Mike Spencer<mspencer at tallships.ca>
wrote:
>> Bruce wrote:
>>
>>> 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.
>> In the mid-70s, I was working in a sports/foreign/performance car 
>> shop.  I visited a friend in Marblehead, Mass. who built formula Ford 
>> engines and watched him use his dynamic balancing machine on 
>> crankshafts that were going into high-performance racing engines.
>>
>> So when I got home, I started researching dynamic balancing because 
>> our existing auto racing customers might be happy to pay for the 
>> service and, as well, there was a lot of off-shore work going on in 
>> Halifax and balancing engine and turbine parts might have been a cash 
>> cow.
>>
>>> As anyone knowledgeable in the field can tell, I'm in over my head 
>>> here.
>> Your (mathematical) head may stand higher than mine but that's what I 
>> found, too.  This isn't something you can cobble together with duct 
>> tape and a TIG welder unless you're Danny Hillis.
>>
>> Find a high-end speed shop, racing engine builder, turbine 
>> maintainance shop or the like in your area and get them to put your 
>> as-good-as-you-can-get-it piece on their machine.  There are just too 
>> many vibrational modes and degrees of freedom to hand-hack it.
>>
>> Or maybe I'm just a wimp, y'know? :-)
>>
>>
>> - Mike
>>
>> --
>> Michael Spencer                  Nova Scotia, Canada       .~.
>>                                                           /V\
>> mspencer at tallships.ca                                     /( )\
>> http://home.tallships.ca/mspencer/                        ^^-^^
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