My misconception about lathe vibration, and how to deal with it.....

[Bart Leetch]

MM You can thump on an I beam with your knuckle and it will ring. Of course it rings louder if you hit it with a hammer. Is this not vibration or am I calling it the wrong thing.
We were working in the attic of our building running new wiring for some lights we installed and I hit my head on a huge I beam that is one of the roof supports. It actually rang and my boss heard it. He made the comment I hurt the beam more than my head. What is it that makes that noise? I may be confused but I think it's vibration. If that's the case then why can't you have vibration at the end of a tool rest with the winter wood hitting your tool at hundreds of times a second.

If that's the case then why can't you have vibration at the end of a tool rest with the winter wood hitting your tool at hundreds of times a second?

Blond answer: Well silly that is because it's winter wood & it's to cold to vibrate.

Sorry I couldn't resist I've been following this thread & it's become to dry & serious.

 

[Bill Boehme]

MM You can thump on an I beam with your knuckle and it will ring. Of course it rings louder if you hit it with a hammer. Is this not vibration or am I calling it the wrong thing.
We were working in the attic of our building running new wiring for some lights we installed and I hit my head on a huge I beam that is one of the roof supports. It actually rang and my boss heard it. He made the comment I hurt the beam more than my head. What is it that makes that noise? I may be confused but I think it's vibration. If that's the case then why can't you have vibration at the end of a tool rest with the winter wood hitting your tool at hundreds of times a second.

John, I'll stifle myself (as Archie Bunker used to say) and not make any comments about the WF beam and your noggin. I think that the Mystery Man's valid point has to do with other folks misapplication of things (even though I truly believe that he is mistaken about shrimp passing gas). Sound is transmitted through water and solids and other media besides air and generally more efficiently. The example of sensors on bridge columns are nothing more than an example of sound being transmitted and the sensors being capable or detecting those small inputs. You could call it sound or you could call it vibration because that is what our ears detect, but your observation wasn't the sort of data that the structural engineers were interested in gathering.

The MM made a valid point regarding vibration that most others failed to appreciate (somewhat his fault for not clearly enough stating what he meant, IMNSHO). Things can't really be considered in isolation when trying to ascertain the source of vibration because it is a close loop system that involves a human in the loop. However, it is safe enough to say that the tool (unless a chatter tool or something left to float at the fulcrum) is not the source, but just a rigid conduit for all reasonable purposes between the two compliant components in the closed loop system -- the human and the thin bowl. From an engineering standpoint, the term compliant refers to something that can't be considered rigid when a force is applied to it. Everything has some amount of compliance, but something that causes a significant enough time lag between stimulus and response to lead to sustained instability .... or to use another word, "vibration" (but, no relationship to the tuning fork vibration caused by twanging a bowl gouge with a hammer) would be the primary causes. There are at least two inputs -- the mechanical drive which is fairly rigid and the human poking the bowl with a gouge. Since the human and bowl both have high compliance the poking force is not constant.

Like I said, the shrimp "wind" thing may be fabrication, but I do know that our sonar could tell precisely where the Ruskie subs were no matter where they were in the oceans because of their noisy screws.

 

[MichaelMouse]

MM You can thump on an I beam with your knuckle and it will ring. Of course it rings louder if you hit it with a hammer. Is this not vibration or am I calling it the wrong thing.

Why are there no chatter marks when the tool's being used on 3/4 thick, or as Hippy mentions, the outside of a piece? All's the same, save the thickness of the wood.

Why is it that with the same extension of the same tool the chatter pattern varies with the velocity of the thin wood? Does a string change its pitch (vibration) when it's plucked more often?

Does choosing a larger diameter tool reduce the chatter?

When someone's innocent enough to believe almost anything Joe Turner with the aura tells him, he needs good information. The solution to chatter has to do with the wood, so let's stay it, dampen it, be gentle with it and solve the problem, not mislead.

 

[Matt Lewis]

....... The solution to chatter has to do with the wood, so let's stay it, dampen it, be gentle with it and solve the problem, not mislead.

And the person poking/turning the wood as Bill mentioned and as was stated way back in the beginning.

Although this article is specifically talking about machining metal, I think folks will find it useful to this discussion. Particularly the info discussing dynamic stiffness, forced input and controlling chatter.

http://www.ctemag.com/dynamic.articles.php?id=236

 

[Dale Miner]

Matt,

That is a good read.

While it does assume machining metal, the principles apply to any material.

 

[Matt Lewis]

Dale,

I concur.

Best regards,

 

[Bill Boehme]

And the person poking/turning the wood as Bill mentioned and as was stated way back in the beginning.

Although this article is specifically talking about machining metal, I think folks will find it useful to this discussion. Particularly the info discussing dynamic stiffness, forced input and controlling chatter.

http://www.ctemag.com/dynamic.articles.php?id=236

It is a good article that does a good job of explaining things to a non-technical audience. I noticed a few errors, but nothing that would matter except to another engineer proofing the article.

 

[robo hippy]

I can get a 3/4 inch thick bowl to chatter/vibrate easily by 'rubbing' the bevel too hard.

Again and again, "the bevel should rub the wood, but the wood should not know it."

robo hippy

 

[Matt Lewis]

Hmmm, controlling the forced input.

 

[Gordon Andrus]

Those were some powerful posts by Dale, but he's just kidding himself if he thinks our turning tools flex to any degree that will have any realistic effect on turning with hand held tools. For a rigidly mounted tool, such as with a metal lathe, and add a long overhang, such as on a wood lathe.......you might see such a thing.......but, for a lathe turner, your hands and arms will move long before the steel will

He answered this well. Our gouges are remarkably like a boring bar on a metal lathe. Harmonic vibration may describe this better than vibration alone, or tool flex. Doesn't adequate mass in the setup, correct speeds and feeds, and tool condition all have an effect. It seems that every part of the operation, the lathe, the tool, the tool post, the banjo to lathe bed connection, the condition of the live center or lack thereof, grain orientation, and lastly and most important the woods' ability to amplify the harmonic vibration are what make the noise and chattering pattern we want to do away with. In my experience with any machine or hand tool, all the above will contribute to the problem of harmonic vibration. I think all can agree that anything that can absorbe, or smooth out the harmonic vibration gives us the best shot at negating its effect on our work. For example, mass in the setup won't stop harmonic vibration if mating parts don't have a good solid surface connection.

 

[Edward Kerslake]

I find that I can almost completely eliminate the impact of vibration of out of round pieces and harmonic vibration but carefully analyzing the piece as it shakes on the lathe. The, once I have a good feel for the frequency, I can move my fingers in and out so that the tool tip matches the flex of the bowl rim. I find that this technique works well up to about 600 rpm but I find it hard to move my fingers sufficiently quickly to exceed 10 adjustments per second...........

(FYI, I am British)

 

[Larry Mercier]

I find this thread very informative and enjoyable. This discussion, which deals with the vibration/chatter issue that we all experience. Most of the participants relate their vast experiences and analyze them. Only one person wants to distract and take this thread off on a tangent. I would like to remind him that President Lincoln said, ( I'm paraphrasing) that any jackass can destroy a barn. I encourage the other participants of this thread to get back to a wonderful discussion. I think Dale Miner said it very well: "My appetite for pig wrestling is over".

 

[Jon Rista]

It never ceases to amaze me, how when you delve into the details of something that seems relatively simple or innocuous on the surface, involves so much complexity.

Very informative thread. Dale's posts in particular were very enlightening. Thank you Odie, for opening the thread so many years ago. As relevant a discussion today I think as it was then.

 

[Edward Kerslake]

I find this thread very informative and enjoyable. This discussion, which deals with the vibration/chatter issue that we all experience. Most of the participants relate their vast experiences and analyze them. Only one person wants to distract and take this thread off on a tangent. I would like to remind him that President Lincoln said, ( I'm paraphrasing) that any jackass can destroy a barn. I encourage the other participants of this thread to get back to a wonderful discussion. I think Dale Miner said it very well: "My appetite for pig wrestling is over".

Larry
My intention was only to inject a little humor and levity as the thread started off with quite a noxious tone.
We can all benefit from a little humor, especially these days…

 

[James McCall]

Larry
My intention was only to inject a little humor and levity as the thread started off with quite a noxious tone.
We can all benefit from a little humor, especially these days…

Ed, I could be wrong but I don't think you were the target of that remark. Earlier in the thread a commenter made quite a few argumentative posts which failed to add much to the conversation.

 

[Edward Kerslake]

Ed, I could be wrong but I don't think you were the target of that remark. Earlier in the thread a commenter made quite a few argumentative posts which failed to add much to the conversation.

Ah, understood and thank you. It's such a great community here that I should be thinking positively. Thanks for setting me straight James

 

[Larry Mercier]

Larry
My intention was only to inject a little humor and levity

Edward, James McCall is correct. I didn't find your humor to be arrogant or obnoxious at all.

 

[Darryn Achall]

May I suggest pumping some iron, and a few ballroom dancing lessons.

Tried both a plenty in the past 60 years. I think that it really does help!

 

[Odie]

Thanks for bring up this discussion again.

This thread has been an interesting look at a moment in time.....13 years ago!

As with others, my knowledge base consists of evolving concepts, and this discussion may not reflect exactly what I currently believe.

One thing I can state with confidence is the results at the lathe I was getting 13 years ago has evolved to a degree that I feel it has improved significantly since then.

Over the years, these discussions have influenced me to alter my views from time to time, and because of that, I feel my understanding and performance has continually been improving.

=o=

 

[Jon Rista]

@Odie Have any more recent gems of wisdom? You've mentioned vibrations in many threads, and I've been curious about that for a while. All the talk about ringing and steel flex earlier in this thread, was quite interesting. I've read in the past that its the wood that rebounds when you get chatter or other issues like that. I always wondered about that, but, maybe it is in fact the steel that is flexing instead.

I know it gets rather arcane, but I find that these kinds of discussions, even when there is a bit of debate, always help suss out useful truths an I always learn something from them.

 

[Odie]

@Odie Have any more recent gems of wisdom? You've mentioned vibrations in many threads, and I've been curious about that for a while. All the talk about ringing and steel flex earlier in this thread, was quite interesting. I've read in the past that its the wood that rebounds when you get chatter or other issues like that. I always wondered about that, but, maybe it is in fact the steel that is flexing instead.

I know it gets rather arcane, but I find that these kinds of discussions, even when there is a bit of debate, always help suss out useful truths an I always learn something from them.

Each piece of wood may react differently because each piece of wood is an "individual".

What works this time, may not be the same the next time.

As far as the hardened tool steel flexing, I'm giving the concept the benefit of doubt.....and doubts I have.

No scientific proof of what I believe influences "the perfect cut". All I can do is observe my results, and adjust when necessary.

=o=

 

[Tom Kamila]

Great thread! Thirty years ago I attacked this vibration problem by wrongfully assuming it was the tools section size and that was partially true. I developed tapered hollow form tools under the idea that the section would increase as the tool overhang increased. It worked great for getting around the beginning of small openings but didn't rid myself of vibrations further in. Now thirty years later and after building acoustic guitars and understanding the concept of resonance frequencies I've taken a different approach. My latest holloing tools are made from 1" x 1" .125 thick square tubing poured full of lead. I still start with my previous tools but about 8" in I switch to my heavy hitters. These are good for about 13" in green red oak. After that I would need a longer and a larger section. In my experience if I want to go deeper I need to "Go big or Go home".

 

[Doug Freeman]

My latest holloing tools are made from 1" x 1" .125 thick square tubing poured full of lead. I still start with my previous tools but about 8" in I switch to my heavy hitters. These are good for about 13" in green red oak.

Some thoughts from an engineering perspective on hollowing bar design:

As the bar is extended from the rest, bending or deflection of the bar is the primary problem not resonance (though resonance can be an issue).

For a given entry hole size, a round x-section will give more resistance to bending. A 1" x 1" bar will fit in a 1.414" hole. Without showing all the equations etc, the important term is "I", called the area moment of inertia. Resistance to bending is directly proportional to "I". For a 1x1 bar, I = .083. For a round bar 1.414" dia, I = .196, which is 2.36x vs the square bar. This is for solid bars. Lead has very low structural strength, and the difference for "I" for a lead filled bar would be much greater, particularly if the bar is filled with lead shot, which provides no structural benefit. There is some structural benefit if the bar is filled with molten lead, but it's minimal.

Try a 1-3/8" solid round bar for your next attempt, you will find much less chatter etc at the same depth. I have a 1-1/8" bar that will get to ~17-"-18" depth depending on the wood. Also, a round x-section will have less friction resistance over a tool rest bar, unless it is a roller.

 

[Tom Kamila]

I have a 1" solid round bar that I can tease to the same distance, meaning taking very light cuts. I can hog out with the square bar at that distance. Now why do we take light cuts? Or why can we take heavy cuts? In my experience the limiting factor is the introduction of vibration. The downward force on the tool while cutting wood is miniscule compared of what that section can ultimately resist before permanent deformation. Now elasticity is another factor as you stated and is what introduces vibration. elasticity I think you will agree is a determining factor when it comes to vibration. Now instead of getting into finite element analysis I just go by seat of the pants experience and work with what's available for what I need to get done. I think we can both agree going bigger will always allow us to go deeper. Also not introduced here is how the bar is supported. I'm very old school and use what is now sold as the Mahone Hollowing kit. The one I have I made my self 35 years ago. At the time it was called something different. In other words the tool is supported by the tool rest and my forearm. My work now has large openings and I rarely exceed a foot in height.

​

 

[John K Jordan]

Although this article is specifically talking about machining metal, I think folks will find it useful to this discussion. Particularly the info discussing dynamic stiffness, forced input and controlling chatter.

http://www.ctemag.com/dynamic.articles.php?id=236

That article is now "not found".

However I do approach a vibrating or out of round wood piece somewhat similarly to the methods I use on the metal lathe - a sturdy tool held rigidly, slow light cuts.

I do think this is a problem with too many variables for a simple one-size-fits answer.

To me, much depends on the type of vibration, the piece, the type of wood, and the geometry (thickness, etc). For pieces not thin and smoothed enough to require hand support and vibration is from out-of-round, I go with standard tools pressed firmly onto the tool rest, good support with the handle or handle arm pressed into my side if possible, and make very light cuts or pulled scraping cuts.

For heavier problem, a thicker tool removing even a smaller amount of wood at a time works well. In many cases I use scrapers, inside or out - the type depends.

Higher speed can help in some cases. Of course, there may be specific speeds that will eliminate or minimize some harmonic vibration.
Slower tool movement may help. I simply try different things to discover what makes me happy.

All this may have been said earlier. This thread is long and my brain is tired.

JKJ

 

[Larry Mercier]

All I can do is observe my results, and adjust when necessary.

Odie, many of your threads show you have an ability to observe, analyze and adapt to your current project's needs. My Chemistry teacher often encouraged us to experiment. I happily and frequently apply his encouragement to other projects. It's fun when experiments turn out to be an improvement.