belt vibration

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  #1  
Old 04-26-06, 07:38 PM
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belt vibration

on my home made sawmill project I have a pully on the engine with a belt going to a shaft on pillow blocks. This belt vibrates alot, its fairly long and was wondering if anyone had any ideas on how to keep the vibration down, would mounting to rubber blocks help?

thanks for everyones help.
 
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  #2  
Old 04-26-06, 08:26 PM
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Hello Michael, I vaguely remember a thread you had about building this sawmill but can't remember what type engine it has. If it is a 1 or 2 cyl w/ a long belt span, it could be the power pulses from the eng translating into the "slack" side of the belt. In other words the side of belt returning to the engine pulley. If trying different belt tensions doesn't stop it, try mounting an idler pulley,such as off a riding mower deck that rides on the wide side of the belt, to the side of belt that is vibrating. It doesn't have to be spring loaded just lightly resting against belt.
If your pulleys and belt are in good shape,the belt probably doesn't need to be as tight as you think.
Hope this helps,
Mike
 
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Old 04-27-06, 09:26 AM
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Is it an actually felt vibration? Or is it just that you can see the belt kinda jumping around between the pulleys? I design belt drives for industrial equipment all the time and most belts on a long span will have some movement in them. As mentioned above, a well placed idler pulley can take a lot of it out and it's almost always on the slack side of the belt. If it is an actual felt vibration, then you will need to closely examine the belt for defects as well as the pulleys.
 
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Old 04-27-06, 03:00 PM
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Its both, I can see it vibrating and you can feel it. Its not enough to hurt anything, its just annoying.
 
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Old 04-28-06, 07:00 PM
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Are you running a single cyl engine?? It's probably the power impulses. I've run into it a lot wit 2 cyl John Deeres. You'll need more rotating weight (a flywheel) to store energy.
 
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Old 04-28-06, 07:09 PM
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its a one cyl 12.5hp briggs verticle shaft
 
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Old 04-29-06, 09:00 AM
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Exactly how long is the belt? Something to consider is the previously mentioned idler pulley on the power side of the belt. BUT, this must be stationary and it must be a V-idler to be effective. How are you tensioning the belt? Simply by sliding your drive (engine) pulley or sliding the driven (powered unit) pulley to obtain tension? I wouldn't recommend this as best. I suggest a spring loaded backside (flat) idler pulley on the slack side of the belt. With this arrangement, you likely will not need a stationary idler on the drive side of the belt, unless the dirve and driven pulley's are small in diameter and then you would want a stationary idler to reduce belt slap. The spring loaded arrangement should remove all vibration. Also, what type belt are you using? 1/2", 5/8", A, B? And, be sure your pulley's match the belt being used. A "B" type pulley using a 1/2" belt will cause twisting and result in vibration.
 
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Old 04-29-06, 07:46 PM
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Puey, I don't understand why you recommend an idler on the drive side. The load will create tension needed on the drive side. Any slack in the belt will be on the "slack" side. Any idlers needed on the drive side are to simply prevent the belt from rubbing on anything in it's path.
Neither Bontai Joe or myself suggested putting an idler on the drive side.
Hopkinsr2, I agree that with a one cyl eng a flywheel is needed. I don't know what dia the driven pulley is but perhaps a cast iron pulley in it's place would help act as a flywheel to store energy from the engine. Michaeljp86,I don't know if this an actual mechanical problem or just an annoyance. If the former,you can buy solid steel pulleys that would definitely act as a flywheel.
Hope all this helps,
Mike
 
  #9  
Old 04-29-06, 07:57 PM
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Its more annoying right now, Im not sure if it will become a problem like vibration cracks. the pullys are about 8" or so and the pullys are about 30" apart. both pullys are made of stamped sheet metal. I dont really care if it vibrates just dont want any trouble down the road and want it to be safe. I need a idler pully for a chain drive on it and I should get this here soon in the mail so I cant really run it much till I get this.
 
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Old 04-30-06, 07:21 AM
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mla2, since we didn't know the size of the pulleys or the length of the belt, I gave a suggestion should michael have had relatively small diameter pulleys with a long, unknown belt type. Lets say he had two 3 inch, "B" groove pulleys spaced 40 inches apart using a 1/2" low power belt with an unknown method of tensioning, driving this unit. This would be insufficient. The purpose of the tension side stationary idler pulley is twofold. 1- It increases the spacing between the drive and slack sides of the belt. 2- It will absorb shock and flutter. This will have absolutely no effective power loss provided a good quality idler is used with good ball bearings.
 
  #11  
Old 04-30-06, 08:09 PM
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Well puey, we all have our own opinions. In the education I have had with V-belt drives(portable rock crushers for a considerable # of yrs)if you install an idler on the inside of a V-belt on the drive side and get too far from the straight line the v-belt should have from drive to driven pulley, you will lose power due to less contact between both pulleys and the belt.Not trying to start something here, just stating what I've learned in 32 yrs. By installing an idler on the outside of belt on the slack side, you actually increase contact area. In my experience I've found most belt slap or vibration will occur on the slack side. I still agree with Hopkinsr2 that a heavier driven pulley will help in achieving a flywheel effect.
My $.02,
Mike
 
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