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Out of round vibration

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My 6 lb out of round spindle (10 inches long) causes my 750 lb lathe to shake at about 900 rpm's. Shaking stopped when I slowed it down.
Does this mean my lathe isn't balanced correctly? Or is this to be expected? Opinions welcome. Thanks
 
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If your lathe otherwise runs smoothly, no I don't think your lathe has a balance problem - although any slight (maybe even a couple thousandths inch) twist induced by an unlevel floor (weight of lathe may be enough to twist it to seemingly sit level) can bring up the problem of harmonics... if you hit the harmonic speed just right, even a few ounces of weight in the wrong place can make a 2,000 pound SUV bounce and shake as you go down the road.. So I'd probably try and see if I can lift up any one corner of the lathe to get any movement (not necessarily lifting it off the floor, just observing if anything shifts) and if you can spot that, there may be your problem.. otherwise it would just depend on how far out of balance that 6 pounds is... (and how big around it is - 900 RPM at spindle center can translate to a LOT of feet per minute that the heavy side is flinging out at.. in other words a 6 inch diameter is going to be rotating a LOT faster on the outside edge than the center is.) easy enough to calculate that edge speed using Pi)
 
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If your lathe otherwise runs smoothly, no I don't think your lathe has a balance problem - although any slight (maybe even a couple thousandths inch) twist induced by an unlevel floor (weight of lathe may be enough to twist it to seemingly sit level) can bring up the problem of harmonics... if you hit the harmonic speed just right, even a few ounces of weight in the wrong place can make a 2,000 pound SUV bounce and shake as you go down the road.. So I'd probably try and see if I can lift up any one corner of the lathe to get any movement (not necessarily lifting it off the floor, just observing if anything shifts) and if you can spot that, there may be your problem.. otherwise it would just depend on how far out of balance that 6 pounds is... (and how big around it is - 900 RPM at spindle center can translate to a LOT of feet per minute that the heavy side is flinging out at.. in other words a 6 inch diameter is going to be rotating a LOT faster on the outside edge than the center is.) easy enough to calculate that edge speed using Pi)

Thanks Brian. I'll read your comments a few more times :)
 

hockenbery

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diameter and offset are important to know.
you might get some improvement by leveling the lathe. But an offset 6x4 will always vibrate at some speed.
an offset 3” cylinder should not vibrate much at 8-900


i do 3 side turnings like the pedestal for globe in my Avitar.
in demos the lathes are never leveled.
i can run 3” one at as fast As I want to go on powermatics. Lighter lathes I have to go slower.

A 6” not so fast.
I do a demo with a 4x6x8 centerd off set by 2” to turn a 4” diameter cylinder with 2” legs.
this always vibrates in demos until I get the 2” cut away then it runs pretty smooth at higher speed as I work the cylinder.
so I have to back off from the speed I could do on my leveled Oneway.

to fine tune the leveling run the out of balance piece at A speed that has a noticeable vibration and move each leveling screw up and down to see if it reduces vibration. Usually one of the four will make a change reducing the vibration or eliminating it.
 
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john lucas

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Yes vibration is always a problem. I have 300 lbs of gravel.inder my 800lb lathe a d it will.still vibrate with out of balance pieces. Now I can usually turn much higher rpm,s with this big lathe than I could with my smaller on that had 400lbs of sand under it. Evey lathe has a limit so you learn to deal.with it. My midi lathe will.vibrate at 250.rpm with an out of balance piece. I can put the same.piece on my big lathe and it wont start vibrating until I go higher than 1200 a d it's still not as bad as the midi.
Lyle jamieson has a great.video.on balancing work before you start the lathe.
 

brian horais

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Doug, I turn out of round items frequently with my multi-axis turning activities. I am always amazed how a small spindle can vibrate my 400+ pound Jet lathe at RPMs between 600 and 900. This is to be expected because as mounted, the spindle is not balanced. My rule of thumb is to advance the RPMs on my off-center turnings until I begin to feel vibration and then back off slightly before I turn the surfaces. As I progress with the piece, it usually becomes more balanced and I can increase the RPMs in small amounts. This works fine and as with most turning, the secret is sharp tools. Even at lower RPMs, a sharp tool will make a nice cut.
 

Roger Wiegand

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Harmonics are fun! When you hit one you can get pretty severe vibration, note that you can escape it by either slowing or speeding up the lathe. Often the latter can be the better choice, depending on the piece involved and how fast you're going in the first place.
 
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Re: John Lucas' comment- I have Lyle Jameison's video on bowl turning. His directions on balance are very easy to follow. Have used it before with success. We are all aware that any piece can be out of balance unless it is a perfect or near perfect cylinder.
 

brian horais

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Harmonics are fun! When you hit one you can get pretty severe vibration, note that you can escape it by either slowing or speeding up the lathe. Often the latter can be the better choice, depending on the piece involved and how fast you're going in the first place.
I agree with the harmonics observation Roger. I usually opt for the slowing down option. Mostly because I'm not brave enough to push through the vibration and seek calm at a higher RPM.
 
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Well, years ago, I figured out, or maybe discovered that my big heavy lathe with lots of sand bags on it had moved from the original spot where I trued every thing up. I looked into it because I was getting more vibration than I was used to. Now, I mark on the concrete floor where the feet are supposed to be. No concrete floor is dead flat, even the ones I poured. That may have happened to your lathe, and/or it may not have had equal pressure on all 4 feet. That is some thing of an art to set up...

robo hippy
 
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Thank you all for your comments and suggestions. Now I have reason to feel confident in solving the cause of my vibration and no longer concerned about any potential problem with my lathe.
I'll look up and watch Lyle Jameison's video on bowl turning.
Again, thanks to everyone for your help.
Best Regards,
Doug Olsen
 
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Your 6 pound out of round spindle will no doubt cause some vibration, compare that to a tire on a vehicle losing several ounces of balance weight and your car wants to bounce down the high way once you get it up to speed. As you increase the speed you magnify the potential energy of the out of balance mass.
 

Emiliano Achaval

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Thank you all for your comments and suggestions. Now I have reason to feel confident in solving the cause of my vibration and no longer concerned about any potential problem with my lathe.
I'll look up and watch Lyle Jameison's video on bowl turning.
Again, thanks to everyone for your help.
Best Regards,
Doug Olsen
I have about 400 Lbs of sand under my 750. Mine would not vibrate at that speed with something that small. Add weight and balance her. Today I started turning a 24 in wide by 9 deep Koa blank. But I chose my 1000 for that one.
 
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I have about 400 Lbs of sand under my 750. Mine would not vibrate at that speed with something that small. Add weight and balance her. Today I started turning a 24 in wide by 9 deep Koa blank. But I chose my 1000 for that one.
I'll have to trek over to Home Depot and pick up some sand bags. Great suggestion, thanks.
My wife and I love Maui, been there three times and spend a good deal of time in and around Lahaina. Envious is an understatement.
Again, thanks for the suggestion.
 
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Well, years ago, I figured out, or maybe discovered that my big heavy lathe with lots of sand bags on it had moved from the original spot where I trued every thing up. I looked into it because I was getting more vibration than I was used to. Now, I mark on the concrete floor where the feet are supposed to be. No concrete floor is dead flat, even the ones I poured. That may have happened to your lathe, and/or it may not have had equal pressure on all 4 feet. That is some thing of an art to set up...

robo hippy
My cement floor is over 40 yrs old, definitely not flat and by nature has developed cracks. Not severe but it makes setting up a lathe difficult. I'll check the weight distribution for equal pressure on each leg. Thanks for the suggestion.
 
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Re: John Lucas' comment- I have Lyle Jameison's video on bowl turning. His directions on balance are very easy to follow. Have used it before with success. We are all aware that any piece can be out of balance unless it is a perfect or near perfect cylinder.
Watched the video last night and tried Lyle's procedure today. Worked very well finding the balance point. Not perfect but close. Thanks
 
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Re: John Lucas' comment- I have Lyle Jameison's video on bowl turning. His directions on balance are very easy to follow. Have used it before with success. We are all aware that any piece can be out of balance unless it is a perfect or near perfect cylinder.
A piece of wood turned to a near perfect cylinder can still be out of balance due to variations in the density of the wood.
 

Emiliano Achaval

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I'll have to trek over to Home Depot and pick up some sand bags. Great suggestion, thanks.
My wife and I love Maui, been there three times and spend a good deal of time in and around Lahaina. Envious is an understatement.
Again, thanks for the suggestion.
You are telling me you have been here and did not stop by to say hello and get a piece of Koa? LOL Suggestion: double and or triple bag your sand. The original bags started to disintegrate and had to rebag the sand. I have it in plastic bags and old sacks of hay cubes, 50# bags. If you have the Bill R Stubby, I made a shelve under there, with an over 100lbs thick steel plate, then added the bags.
 

Emiliano Achaval

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Doug, I turn out of round items frequently with my multi-axis turning activities. I am always amazed how a small spindle can vibrate my 400+ pound Jet lathe at RPMs between 600 and 900. This is to be expected because as mounted, the spindle is not balanced. My rule of thumb is to advance the RPMs on my off-center turnings until I begin to feel vibration and then back off slightly before I turn the surfaces. As I progress with the piece, it usually becomes more balanced and I can increase the RPMs in small amounts. This works fine and as with most turning, the secret is sharp tools. Even at lower RPMs, a sharp tool will make a nice cut.
Do you ever turn anything that is not out of round? LOL If anyone has experience with unbalanced work, that would be you! It is nice to see that you found your signature work, I can tell a piece is yours when you post pictures, without reading about it. Keep up the great work. Aloha
 

Emiliano Achaval

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Not to be a nitpick, but the proper term for the phenomenon is resonance, not harmonics. See my post in the Tips and Tutorials forum for an explanation of the two terms.
Thanks for the reminder. It is not nit-picking, I like to call things what they really are.
 

Emiliano Achaval

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It is worth mentioning that if you have the Bill R Stubby, with his base, they are easy to have them on 3 legs. Get a hold of the headstock and pull hard on it. You should not be able to rock it, even just one MM. I use a car floor jack to balance mine. Once leveled and balanced, try rocking it. Should not move at all.
 

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Not to be a nitpick, but the proper term for the phenomenon is resonance, not harmonics. See my post in the Tips and Tutorials forum for an explanation of the two terms.
Resonance is a phenomenon that can occur at the fundamental frequency of an oscillating system or at any of the overtones. Harmonics is, I think, a more general term to describe the various frequencies at which resonance can occur. I used the word I intended to use (I think correctly, but I could be wrong!), sorry if it created confusion. I don't think it is inconsistent with your earlier explanation.
 
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I'm with Roger - I use the term Harmonics as that is the terminology I was trained on at Ford factory training school (Gosh must have been 20 or 25 years or so ago) during the NVH diagnostics classes (NVH - Noise, Vibration & Harshness) In other words, harmonic vibration (and they call the counterweight on the front of car engines the Harmonic Balancer, BTW) may occur at many various RPM's - Often multiples of the specific resonant frequency - So, a vibration that happens at 600 RPM resonance likely might also occur at 1200 and 1800 and 2400 RPM's too - and often magnified much more than the mulltiplier might imply..
 

john lucas

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I used pea.gravel.under my lathe. I have. Ever been able to keep.sand in any kind of container and not have it leak. Last.time I used sand I got the bags they used to hold down the tarps on baseball diamonds. I filled those and and 2 years later when I had to move that lathe I was amazed how much sand had somehow leaked out.
 

Dennis J Gooding

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Brian, I don’t believe that there is any real conflict here. The term ”harmonic” in your case and in many others is simply short hand for “vibration at a harmonic frequency”. Harmonic frequencies are integer multiples of the fundamental frequency. In the case of a lathe with an unbalanced load, the fundamental frequency is the frequency of rotation of the spindle.

By the way, a freely spinning unbalanced load on a lathe would produce vibration at the “fundamental” frequency, and very little at any harmonic frequency. Only when one starts to cut, interrupting the smooth turning of the lathe, do harmonic vibrations begin to appear. An extreme case would be when turning a cross-grain piece. In this case, the cutting load would repeat twice in each revolution and would produce driving force at the second harmonic of the spindle speed.
 
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Lets assume that I have the weight perfectly balanced between all 4 feet. Do I need to rebalance after adding 500# to the shelf under the ways? What should I do if I rotate or move my head stock? I start a piece between centers. Do I need to rebalance when I mount it in my chuck? Are we over thinking this?
 

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The purpose of "balancing" the legs is to insure that all are in firm contact with the floor. There is no practical way to measure the weights on each leg. In any case, if all feet are in firm contact with the floor, the weight on each is determined by the weight and geometry of the lathe. As long as the center of gravity of the added weight lies within the foot print of the lathe, it will increase the weight on all legs. Therefore, unless the floor itself is not stable, there should be no reason to re-adjust the legs.
 
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Re: John Lucas' comment- I have Lyle Jameison's video on bowl turning. His directions on balance are very easy to follow. Have used it before with success. We are all aware that any piece can be out of balance unless it is a perfect or near perfect cylinder.
I have watched that video and found it a great resource. I have my bowl blank balanced but my midi lathe still like to vibrate some.
 
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Another option is to add counter balance weights to the piece being turned. In the mechanical world it is a common practice to install
a stainless steel hose clamp on a drive shaft to fine tune the balance and reduce vibration. Some woodturners using a face plate will
secure counterbalance weights to the face plate when they have an out of balance billet or an off-center turning.
 
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