Thread: Balancing a fan
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Stu Fields Stu Fields is offline
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Default Balancing a fan


"Karl Townsend" wrote in message
anews.com...
I got so much help on my sprayer, I'm trying again...

Full time investigation and part replacement has me working on this theory
of the problem cause: The squirrel cage fan is out of balance. It is
barely detectable because the fan has a 2" solid steel shaft and some
serious pillow block bearings mounted solid to a beefy frame. At the
resonate RPM, this imbalance feeds on the slack in the drive line. Any
system upset causes the fan to become unstable and it lurches back and
forth.

I've called around and not found a place to dynamic balance something like
this. Are there any home brew methods? Or other suggestions? Its built so
solid I don't think I'm looking for a minor imbalance.

Karl


From the text Mechanical Vibrations written by Den Hartog: If you have an
out of balance shaft rotating at less than the "Critical Speed" and you
approach that shaft with a pencil or a felt tip pen, the mark will be made
on the "heavy" side. Add wts to the opposite side from the mark. However
if the shaft is rotating at more than the "Critical Speed", your pencil/felt
tip pen will mark the light side and wts must be added to the same side as
the mark. If you are unfortunate enough to have the shaft rotating at the
"Critical Speed" the mark will be made 90 degrees after the heavy side.

This concept has helped me balance helicopter main and tail rotors down by
factors of 4 below the normally acceptable levels. However I do have an
electronic balancer that uses velocimeters to measure the magnitude of the
vibration and a photo sensor to give me the "pencil" mark.
We did have a subscriber to our magazine that balanced his tail rotor using
just a dial indicator and a graphic technique developed by the Russians. I
think that I could make a copy of the article describing that technique
available if you want it.

Stu Fields
Experimental Helo magazine.