[TheForge] A Balancing act

[Steve Bloom]

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 - which 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