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

Discussion in 'Newbie' started by odie, Dec 30, 2012.

  1. odie

    odie

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    At one time, a couple decades ago, I had thought all vibration created and felt at the lathe could be dealt with by absorbing it through the addition of anchor bolts, weight, sand, metal, whatever.........but, this just isn't so. I'm relaying this information so that if there is anyone else thinking along the lines of what I once did, they could be redirected to a different way of thinking about this subject.

    Adding weight, mount bolts, etc., to your lathe will help eliminate the kind of vibration created by an out of balance condition.......or, unequal centrifugal forces, simply by not allowing the lathe to move. That's it, end of story..

    There are two types of vibration in lathe work......as mentioned, there is unequal centrifugal force created by an out of balance condition, and then there is that vibration which has as it's root source, contact between the wood workpiece and your cutting tool.

    That I know of, there are only two attempts at a mechanical fix to the vibrations created between wood and cutting tool.

    One of these is lead shot in the handle of your tool. Honestly, I've never tried this, but reasonable deduction will conclude that lead shot in the handle will not eliminate vibrations created at the cutting edge........all it will do is absorb the felt vibration in your hand. I consider this a gimmick.......If there is vibration being created, then deal with it at the source, not how it's felt in your hand.

    The other mechanical fix to vibration, is a bowl steady.....(or, using your fingers.) I have a couple of bowl steadys, and they do work......but, only to a point. They work by reducing the flexing action of the wood itself. I stress that bowl steadys cannot completely prevent vibration, but they can certainly prevent it sometimes, and at other times, reduce it.

    Bowl steadys are a worthwhile thing to have.....

    .....and, adding weight, and/or using anchor bolts are worthwhile things to do, as well.......Not much you can do about preventing the forces applied to your lathe by an out of balance condition, but you can prevent the resulting movement of your lathe with weight and a solid mount.

    The most important point in this post is to stress that.....The best way to help eliminate, or reduce any vibration created by the cutting action of tool to wood, is to have sharp tools presented well.

    ooc
     
  2. MichaelMouse

    MichaelMouse

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    Careful now. It's not the 1/4" thick bowl sides that vibrate, as we know so well. It's the 1/2" steel cylinder that's trying to cut them. :rolleyes:
     
  3. odie

    odie

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    MM.....

    Once again, as is your usual, you interpret what you'd like someone else to have said, so that you can disagree with an assumption.......and appear enlightened.

    Yes, thin wood vibrates......(This is where fingers and bowl steadys shine!.....you did catch that part, right?) When thin wood vibrates, so does the tool.

    I'll add that thick wood, as well, when experiencing those "spiraling ridges" will make that 1/2" steel cylinder.......vibrate.

    In either case, whether the tool or the wood is where the source originates, the tool will vibrate.

    Anyway, you should re-read that bold part of my post that explains the cure for vibrations originating at the cutting action of tool to wood. This is the solution, whether it's the tool, or the wood that's causing the vibration.

    ooc
     
  4. MichaelMouse

    MichaelMouse

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    Wasted breath I guess. One of the many myths of turning - the steel vibrates, not the wood. Isn't true. Especially when you consider that the wood in question isn't supported by anything (normally) while the steel is supported an inch back on the rest.

    Lighten up.
     
  5. odie

    odie

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    Interpreting incorrectly, so that you can disagree, is your MO, MM......:D

    Nowhere did I say the steel itself is the source of any vibrations......it's the sharpness and presentation of that steel that is.

    I did say the wood flexes and causes the tool to vibrate......and, I also said that spiraling ridges will cause the tool to vibrate. In all cases I did indicate that sharp tools and good presentation is the solution.

    ooc
     
  6. john lucas

    john lucas

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    Odie I think he poking fun saying that 1/2" steel bar will not vibrate when compared to a 1/4" wooden bowl.
    Of course the steel actually can chatter when pushed to far over the tool rest. When I was doing larger inside out turnings I often had to extend 3" or more over the tool rest. My 1/2" bowl gouge will chatter but my 1/2" detail gouge won't. Both are made of the exact same steel and size. the only difference is the depth of the flute. The detail gouge has a very shallow flute and consequently chatters less.
     
  7. odie

    odie

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    John......considering MM's history, you may be extending credit where the evidence points elsewhere.

    When you extend a detail gouge a long distance over the tool rest, and it doesn't chatter, where a bowl gouge does, what do you account for that?


    ooc
     
    Last edited: Dec 30, 2012
  8. john lucas

    john lucas

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    It's simple. It's the thickness of the steel. The bowl gouge is only about 1/4" thick at the bottom of the V. The thickness of the walls of the V make it sturdier than my U shaped gouges but not by much. The Detail gouge is much thicker since the flute is so shallow. It's almost like using a fully round piece of 1/2" bar stock.
    I also have a 1/2" spindle gouge from Thompson that is made from the same bar stock. It will chatter at least as much as the bowl gouge if not more. Again it's because the metal is simply not as thick once it's milled to shape.
    Now obviously if you can find a way to not extend the gouge over the tool rest then you reduce the chatter a lot. I used to demonstrate the difference when I turn my mirrors. I use a spindle or detail gouge with the flute pointing straight out to undercut the mirror opening for wood movement. I just push the tool in and then twist it clockwise which brings the bottom lip up into the wood and cuts the V shaped undercut. With my Sorby 3/8" spindle gouge I get loud screaming chatter that hurts your ears. With my Thompson 3/8" detail gouge it's all gone.
     
  9. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Odie, I think that your observations are right on the money.

    I do try to balance pieces, but circumstances may not always allow that to be possible.
     
  10. Matt Lewis

    Matt Lewis

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    Is vibration the correct term for what is being described? I wonder as I am reading this as more of a result of the tool not being able to stay fixed/ridgid like in the carriage on a metal lathe vice oscillation from equilibrium (vibrating) of the tool or its tip. Thoughts?
     
    Last edited: Dec 30, 2012
  11. odie

    odie

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    Interesting observation, John......

    Assuming your detail gouge has the same grind to it, requiring the same presentation, and it is more suitable for the specific purpose........can it be assumed that mass is the determining factor?

    Longer reaches are usually accomplished by going to a size larger bowl gouge that will naturally overhang the tool rest with a bit more control, because of it's mass.......not that you are doing anything wrong. On the contrary, because in lathe turning, it's the results that count.

    ooc
     
    Last edited: Dec 30, 2012
  12. odie

    odie

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    Thanks, Bill.......

    My observations were the incorrect belief that I could deal with vibrations that had a root source at the cutting action between tool and wood by further stabilizing the lathe with weight, anchor bolts and etc. I began doubting my beliefs years ago, but with the help of other turners, my understanding became clearer.

    Believe it, or not........you, John, and even MM have helped me in ways you probably are unaware of......among many other forum participants who have contributed to my evolution as a turner. I believe I have helped a few others, as well......:)

    As you do, I try to balance every piece of wood the best I can.......some are very close, some are not so close. I currently have my lathe bolted to the concrete slab floor, and that seems to suffice for my needs. I don't do very many "out of balance" pieces.......

    ooc



    Perhaps so, Matt..........to tell you the truth, I'm not sure I understand what your meaning is. If you are referring to tool overhang from the toolrest, then you and John may be speaking of the same/similar thing, but using different terms, or thought process.

    If you are speaking about the tool itself being held solid (ie: metal lathe) versus a tool which is hand held by the user against a toolrest.....then the term "vibration" may not be the most descriptive word to use.......what would you suggest?

    ooc
     
  13. Matt Lewis

    Matt Lewis

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    Odie,

    You are correct about my thought, but I failed to combine John's. I think it is a combination of both. Certainly there is vibration if the inappropriate sized tool for a given overhang is used regardless of the tool's sharpeness or quality of presentation. But, I think there is also an element of movement that isn't really vibration that is caused because of a human's inability to keep the tool ridged or fixed at the fulcrum (even when it is a moving fulcrum) as the whirling mass strikes it even if the tool is of appropriate size to not have vibration due to extension over the rest. Perhaps we can refer to this as irregularities in feed rate in addition to tool vibration. Am I making sense?
     
    Last edited: Dec 30, 2012
  14. odie

    odie

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    Yeah.....perfect sense.

    You are absolutely right.....there is the human factor to consider.....and we all make imperfect machines! :(

    May I suggest pumping some iron, and a few ballroom dancing lessons? :D

    In all seriousness, though ......we need to do everything in our power to make the "perfect cut" with artistic precision. Take a look at some of the other fine turnings being produced, and you know there are quite a few people who've discovered the "secrets of the universe"! Heh,heh,heh! :cool2:

    ooc
     
  15. MichaelMouse

    MichaelMouse

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    John, would you say it's a bit of a stretch , no pun intended, to say that you could bend the steel? You see, the third part of the problem is neither the wood not the metal, but the flesh. When you're hanging way out, you are giving away almost all of the mechanical advantage you would have had if you were employing the tool and rest properly. When it bumps or dips, you try to compensate, often, as folks who have their gouges misplaced, overshooting and provoking a secondary.

    Not that this would lead to "vibration" in the steel anyway, because you'd have to somehow flex that short section between the fulcrum and the point of applied stress. Fancy twanging a 1/2" thick metal string only 3 inches long? Betting it wouldn't even ring if you hit it with a hammer, and that's a lot more force/unit area. Thoughts on beams http://en.wikipedia.org/wiki/Beam_(structure) Cantilever loading. http://www.efunda.com/formulae/solid_mechanics/beams/casestudy_bc_cantilever.cfm

    Another myth, which you're repeating, is that grinding a flute in the gouge weakens it significantly, permitting the flex that eludes science when the bar is solid. If you're cutting with the nose, or near nose of the gouge, the section opposing the rotational velocity is a C-channel type beam, and isn't going anywhere. While weaker in the "chips flying" or paint lid pry mode, you're still dealing with the edges of the flutes stiffening the whole (U beam), not just what's left of the steel on the bottom of the flute.

    The chatter comes from the wood recoiling or the hand bouncing, not from the metal flexing. No emoticons, just fact.
     
    Last edited: Dec 30, 2012
  16. MichaelMouse

    MichaelMouse

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    Thus the old technique of swinging the tool into and through an extremely irregular surface. The human has the best control with the one hand simply pinning the tool to the rest, while the other arcs the business end through the high spots. it's the shoulder/hip swing which locks the small, and uses the large muscles which can better resist the irregularities. Once the surface is regular enough to allow the bevel to be used as a guide, the tool may be advanced, but it is no where near as stable to advance with that fulcrum hand as it was to swing with the lever hand.

    People who do not take advantage of the overhand grip are even more vulnerable to irregularities in the surface, or variations in frictional forces which cannot be anticipated, nor resisted by the small muscles pushing the tool.
     
  17. Dale Miner

    Dale Miner

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    There are no perfectly rigid materials. Of course the steel flexes and as a result, will have a harmonic vibration frequency. The frequency and amplitude will change depending on many factors, not the least of which are the cutting force and the length of tool over the rest. Both the wood and the tool flex to varying degrees, and the vibration of each or both can affect the surface pattern on the piece of wood. Adding weight to the machine will help resist the machine moving about from imbalance (although it does not reduce the forces from the imbalance). Adding stiffness to the machine and tooling helps resist exciting harmonic frequencies resulting from the cutting action.

    A boring bar held in either a captive rest or a heavy boring bar on a metal cutting machine does not have a human flesh factor and will vibrate. The bar itself is a tuning fork and will vibrate. A bowl gouge is no different. Statements that the gouge does not flex are contrary to the laws of physics.

    Typically, when a pattern is imparted on the surface, the pattern helps to excite the frequencies that the bar and the part vibrate at, making the surface texture more pronounced, and subsequently, exciting the frequencies to greater amplitudes, etc, etc.

    Lightly rubbing fingers or a paper towel on the outside of a bowl when hollowing does little to resist the cutting force, but instead acts like a shock absorber and dampens the virbation much like shot in a tool handle. Energy is absorbed/dissapated by the flesh or shot and results in the amplitude of the vibration being reduced, and to some extent, the frequency being changed. Recucing the amplitude reduces the exciting force, which reduces the texture that reduces the exiting force, etc, etc. A bowl steady works in a similar fashion. The support wheels do not need to be exactly opposite the gouge. Contact with the bowl in an area near the rim changes the ring frequecy, absorbs the higher frequency vibration energy, and helps prevent the formation of a pattern that excites the system. The resulting reduction in amplitude and frequency allows for turning without a noticeable pattern.

    Often times, changing the rpm between passes by a small percentage will help reduce the surface pattern. The change in rpm will present the surface pattern to the tool at a different frequency, and break the harmonic pattern caused by the previous cut.

    Sharp tools well presented. Couldn't agree more.
     
    Last edited: Dec 30, 2012
  18. Ian Robertson

    Ian Robertson

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    What he said.:D
     
  19. MichaelMouse

    MichaelMouse

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    So you get the chatter with the same gouge when you have 1" of an inch of wood, or does it start at 3/8? Anyone?

    Does the gouge still vibrate and make its chatter pattern when a steady is placed? Once again, anyone?

    Does raising the heel to gain some clearance angle on the gouge instead of "riding" the surface irregularities in ring-porous woods (or scraping razor thin with no bevel at all) take away tool "vibration?" Anyone still playing?

    Repeating this foolishness about sliding wood bending steel can only mislead people who encounter the problem of chatter into thinking it's the tool, and there's no hope, when it isn't.

    BTW, I think it's about time we did away with the Normisms. Nobody wants anything but "a nice sharp chisel."

    Well, maybe one guy. ;)
     
  20. Dale Miner

    Dale Miner

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    Point, Counterpoint

    Remember the episodes with Jane Curtin and Dan Akroyd? How many times have we wished for the ability to throw political correctness out and reply accordingly.

    Mickey Mouse,

    In the first line of the text from me that you quoted you must have intentionally not read the word "varying". Pick and choose, argue and change the subject, spew misinformation as you will. When you are wrong, none of your usual tactics will change your status.

    The answer to your first question is yes, although you are forced to accept the varying part of the equation. As the wood becomes thinner and less able to self dampen vibration, the texture from the resonance of the wood leaves a pattern that causes a varying cutting force that will cause the gouge to flex/vibrate from the varying force. To ignore that condition is unrealistic. To say that it occurs but has a minimal effect may be valid at times, invalid at other times.

    The answer to your second question is yes the gouge flexes, and as such leaves a pattern. The pattern may or may not be problematic.

    The answer to your third question is no. Taking a very light cut reduces the cutting force, and as a result reduces the forces that are exciting the vibration. "Riding" the bevel does not fit the description of "well presented" for most people that understand the concept. Light bevel contact, or floating the bevel would be a proper description of the pressure between the bevel and the wood. Also, it would be very difficult to believe that you have never experienced vibration in a scraper. After all, isn't that the premise of a chatter tool? Varying, remember?

    No one said anything about bending. Bending would involve plastic deformation of the tool. Flexing does not leave the tool with a permanent bend anymore than snapping the tine of a tuning fork with a fingernail leaves the tuning fork permanently bent.

    No hope? Not hardly. A sharp tool well presented covers a wide range of parameters. Somewhere within those parameters there is more than hope, there is a solution.

    As to still playing; I don't see this as a game. This forum is for the exchange of information regarding woodturning. To explain that the entire system can and does have an effect on the process was the purpose of my original reply to this thread. Each component of the system has an effect on the final result. Many times one component will affect the function of other components. While a simplistic overview that only the wood has an effect on vibration may be easy to grasp, that overview is wrong.

    Inaccurate or faulty concepts are discounted by those with experience. For those starting out, information garnered from forums can be helpful if accurate, and something less than helpfull if inaccurate or incomplete. Not always, but usually, I find the information you present to fall into the inaccurate or incomplete category.

    Let's continue this without the cloak of anonymity, shall we? My appetite for pig wrestling is over.
     
    Last edited: Dec 31, 2012

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