[TheForge] A Balancing act

[Peter Fels & Phoebe Palmer]

Good Mike:
Might as well toss in that, aluminum pulleys can wear irregularly with use, harder material to a lesser degree.
Also, rubber V belts sometimes wear unevenly , especially around the lap joint.
Last, if someone balanced the wheel with brazing rod and nothing warped…Then the amount of air resistance on individual vanes could also be irregular.

I shudder when i imagine balancing jet engine fans.

On Mar 5, 2015, at 3:06 PM, CGRAF <adveniam at att.net> wrote:

Again this is just me hitting the simple stuff first.
How old is the belt and how often is the blower run?

Old belt can look perfectly fine but be stiff. If it sits wrapped around the pulleys it can develop pretty substantial humps. Things can bounce pretty good. speed would affect it.

Belts are pretty cheap. Also try futzing with the belt tension.

I am not trying to insult you with these suggestions. Actually really bright people often go straight to the complicated answers.

Mike Graf

On 3/5/2015 3:49 PM, Peter Fels & Phoebe Palmer wrote:
> Steve;
> If you literally have rattling, then something’s loose , plus out of true, or balance , or your bushings/bearings are shot.
> 
> On Mar 5, 2015, at 1:34 PM, Steve Bloom <sabloom at ironflower.com> wrote:
> 
> On 3/5/2015 9:55 AM, CGRAF wrote:
>> How sudden was this?
>> How exactly is the motor power transferred to the blower?
> It's been a slowly growing concern -- it was never quiet but 'rattling' is fairly new or maybe I'm just hearing it more since I have been teaching a bit and that means less earplug time.
> 
> The unit is an old large (18" snail) champion blower with ~10" diameter blades propeller running on a 0.75" keyed shaft.  The shaft is ~ 18" long with one pillow block almost touching the side of blower and the other ~ 12" away. A pulley is midway between the blocks and talking to a 1 HP 120V motor. The ratio of the pulleys and the motor's speed generates ~ 3400 rpm.  Run by itself, the motor is virtually silent. The shaft appears to be straight (based on spinning it on a lathe) and hand spinning the unit is easy - no resistance and no sound (of course, that's at maybe 60 rpm).  The sound is present with or without the "snail" bolted in place.  The fan has obviously been balanced in the past, i.e. globs of weld/braze on some of the fan blades.  Immediate 'cure' is to ignore it or slow the rpm down.  Eventual solution could be to beef up the shaft (1.25" shaft turned down to 0.75"), opening the access port in the backing plate for the larger shaft, and replace the pillow blocks - w
hich will probably mean redoing the mount system.   The obvious first step is to dynamically balance the fan - if I can figure out a reasonable procedure.
> 
> I've posted a few images at ironflower.com/ironwork/blower.pdf
> 
> Steve
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