balancing a squirrel-cage blower

I recently purchased and had installed a 7000cfm evap. cooler. Upon starting for the first time, it has a very objectionalble vibration, indicating the
blower is not balanced properly. I complained to the mfg. and they sent out another one, but I would like to check the balance on it before I install it. This is a 16 in. Dia. by 20 in. long blower, driven with a 1hp motor. I have tried to do it with v- blocks for the shaft to roll on to see which side ends up on the bottom, but am not haveing much luck.
Any suggestions will be appreciated. bob
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Instead of V-blocks, you'd get less friction of you set up two level flats for the axel to roll on. This is assuming you have a blower cage with axel sticking out of both ends...
If not, can you mount it up but leave the motor disconnected, so it spins free?
Dave
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bob writes:

Static balancing won't do.
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On Fri, 18 May 2007 16:56:21 -0500, Richard J Kinch

It might do. It is possible to have a rotor that is statically balanced but dynamically imbalanced, but if the only imbalance present is static then static balancing will correct it. Put half of your static balancing weight on each end of the rotor, or all of it at the axial middle of the rotor.
Dynamic imbalance with static balance occurs, for example, when there are equal imbalances on opposite sides of opposite ends. This isn't detectable unless the rotor is spinning.
Static imbalance would cause the whole rotor to "hop". Dynamic imbalance creates a moment that makes the ends of the axis want to wobble in opposite directions when spinning.
Once you have statically balanced it, you might be able to dynamically balance it by using a neon or fluorescent light as a strobe while spinning the rotor. If you can visually slow or stop the rotor then you can see where to place dynamic balancing weights relative to marks on the rotor. They should be equal in size and placed opposite one another, e.g., one at 12 o'clock on one end and the other at 6 o'clock on the other end.
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Don Foreman wrote:

IF you just had a good way to measure the amount of unbalance, you could move a weight around to get the minimum vibration. First do one end of the rotor and then do the other. Move it one way and if it gets worse rotate the position the other way until you get the minimum reading. Then do the other end of the rotor the same way.
This was how tires were dynamicly balanced on a car with the balancing unit that bolted on to the wheel. There were four little rings that, if you held them the internal weights inside the balance unit would move around. I always put a cup of coffee on the fender to see the amount of vibration. The amount of weight and position would show up in a little window on the balance unit.
John
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replying to Richard J Kinch, samuel godoy wrote: hi bob we A 22'' ALUMINIM WHEEL THE NEED TO BE BALANCE
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Are you positive it is the blower? It could easily be the motor/ pulley/belt system. If you remove the belt and spin the motor by hand, while sighting across the diameter of the pulley sheaves, is there ANY lateral deviation? Same test for the fan pulley. This is called "lateral runout"; many, many automobile wheels suffer from this also. Anything visible will make your whole house vibrate like crazy.
Then: Install the belt, hand turn the whole thing while looking closely at the outer surface of the belt on both pulleys. is there ANY "up-and-down" movement? Anything visible will make your whole house vibrate like crazy.
Be VERY suspicious of pulleys and belts you buy at any "home improvement" store. Most are very seriously warped, bent, mis- machined because they were manufactured by people who have no clue about their application. Your swamp cooler's fan probably has a different source.
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replying to webpa, warminredding wrote: what size pulley do i need on my squirel cage if the motor is a 4 inch?? Motor gets warm and shuts downm.
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On Sun, 17 Jul 2016 14:18:03 +0000, warminredding

Oh, about yea by yea ought to do it. And make sure you don't have any kinks or knots or coils in your power cord. You'll lose power and cause the motor to get warm and shut down.
--
The ultimate result of shielding men from folly
is to fill the world with fools.
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Sun, 17 Jul 2016 14:18:03 +0000 typed in rec.crafts.metalworking the following:

    Firstly, about the motor. Is the motor 4 inches, or the pulley on the motor? What is the rated speed or power of said motor?
    Secondly: what size pulley is on the squirrel cage? How big is the squirrel cage? How fast do you want the squirrel cage rotating for "optimal" effect?

    Sixthly: How much ventilation/cooling does the motor get? What sort of temps is it exposed to "just sitting there"?
-- pyotr filipivich "With Age comes Wisdom. Although more often, Age travels alone."
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replying to pyotr filipivich, piperat wrote: 4 inch pulley on the motor, 12 inch on the squirel cage, 1/2 hp 2 spped motor not sure of the rpm;s cant read it. is inside the swamp cooler so should have plenty ventalation. Runs very slow want to speed it up a bunch.
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Been there, done that. You're wise to check the replacement. I assume you got a replacement drum and not the whole blower or else testing would be trivial. My replacement drum was also out of balance and in hindsight I would have been far better to return the whole swamp box to the retailer and swap it for a different one.
Art

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bob wrote:

A lumpy fan belt will give you a fit too..
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I bought an inexpensive wood lathe a few years back. I dumped it out of the box, built a nice stand for it and turned it on... And it shook like there was no tomorrow. More than a little irritated, I was about ready to tear it down, box it up and return it, but I played around a little with it and found about a quarter inch of "S" curve in the belt. I went over to the local auto parts store, paid a couple bucks for a new belt and it ran as nice and smooth as can be...
Jerry
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bob wrote:

It will be hard for you to balance the blower without the proper equipment. First, the only way you are going to get the vibration under control is to do a two plane balance on the thing unless you want to do a trial and error type balance by adding and removing little weights to the cage.
With dual trace scope, a displacement sensor and a optical sensor you could do it but if you are not really familiar with the use of this equipment you will be wasting your time.
Optical sensor will give you a zero reference with a white mark on the shaft reflecting a light beam.
the displacement sensor coupled to the second input will give you the angle of the imbalance by the relative position of the pulse in relation to the reference pulse and the height of the scope trace will give you a relative amount of unbalance.
A static balance will not work because of the width to diameter ration of the blower.
For instance: if you have a long shaft with a weight on an arm attached to one end and the same weight and arm attached to the other end 180 degrees apart, the shaft will be statically balanced, but if you try to rotate it, the centrifugal, centripetal ( pick your force :) ) will pull one end of the shaft in one direction and the other end in the opposite direction causing a vibration.
There are several ways to do a two plane balance, using two sensors is one way. I would add weight on one side of the wheel until you get a reversal of the position of the pulse position, then add weight on the opposite side until the pulse diminishes to an acceptable level.
Unbalance is rated in a force x distance. i.e.. Inch oz. gram centimeters.
John
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replying to John, Breadman wrote: Ok friend, I'm that guy who still logs around a 15 meg two channel scope even though I'm working on a farm. A farm with giant squirrel cage blowers that need balancing, thanks for the unexpected direction and for sharing your wealth of knowledge. So many know it all people around today it'll be a miracle if we make to the next decade.
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Is the motor rubber mounted? - if so, did you remove the keeper bolts holding it locked down during shipping? - its on page 357 of the instruction manual.
(Well, it was on page 357 on mine - or thereabouts. Spent AGES chasing a non existent fault...)
Andrew VK3BFA.
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bob wrote:

Instead of vee blocks, use knife edges, any straight, flat, narrow edge. That will provide a surface for the shaft to rotate on with litle or no friction.
Jim Chandler
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replying to John, Breadman wrote: Ok friend, I'm that guy who still logs around a 15 meg two channel scope even though I'm working on a farm. A farm with giant squirrel cage blowers that need balancing, thanks for the unexpected direction and for sharing your wealth of knowledge. So many know it all people around today it'll be a miracle if we make to the next decade.
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