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

[Odie]

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

 

[MichaelMouse]

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.

 

[Odie]

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.

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

 

[MichaelMouse]

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.

 

[Odie]

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.

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

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

 

[john lucas]

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.

 

[Odie]

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.

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

 

[john lucas]

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.

 

[Bill Boehme]

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

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.

 

[Matt Lewis]

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?

 

[Odie]

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.

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

 

[Odie]

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.

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

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?

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

 

[Matt Lewis]

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?

 

[Odie]

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?

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?

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

 

[MichaelMouse]

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.

 

[MichaelMouse]

Odie,
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 (SNIP) Am I making sense?

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.

 

[Dale Miner]

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.

 

[Ian Robertson]

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.

What he said.

 

[MichaelMouse]

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.

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.


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.

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.

 

[Dale Miner]

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.

 

[Matt Lewis]

I am thinking that any vibration of the steel is very small and likely not of major concern to the turner. To me the bigger problem is control of the "feed irregularities" which I suppose falls under the tool presentation category. In other words, it is a bigger matter to maintain consistent orientation of the cut with regard to rigidity in relation to the fulcrum. Of course sharp tools are a necessity, but I think are more important to the turner with regard to "feed irregularities" than any vibration that might be enhanced in the steel. Try turning a piece of Aluminum on the wood lathe and see how hard it is to keep the tool fixed so that it maintains consistency of the cut. Although a sharp tool improves your chances as does keeping the tool rest very close to the piece, you will most likely have some chatter marks because of your inability to keep the tool fixed with regard to its cutting orientation rather than because of any small amount of vibration that is occurring in a naturally flexing, but very ridged piece of HSS. I suppose really what I am saying is that I think the vibration within the tool steel that does occur is at a microscopic level and really not as big an issue as the macro level movement of the tool orientation that is inevitable in free hand turning provided you have employed other measures such as limiting tool rest distance in relation to the tool's girth/thickness. I think that any pattern forming on the wood is more likely a function of wood flexing and feed irregularities than tool steel vibration. That is why I wondered about the use of the term vibration because to me vibration is an oscillation from equilibrium about some mean value which I don't believe is necessarily what is happening with the tool orientation itself.

 

[Odie]

I am thinking that any vibration of the steel is very small and likely not of major concern to the turner. To me the bigger problem is control of the "feed irregularities" which I suppose falls under the tool presentation category. In other words, it is a bigger matter to maintain consistent orientation of the cut with regard to rigidity in relation to the fulcrum. Of course sharp tools are a necessity, but I think are more important to the turner with regard to "feed irregularities" than any vibration that might be enhanced in the steel. Try turning a piece of Aluminum on the wood lathe and see how hard it is to keep the tool fixed so that it maintains consistency of the cut. Although a sharp tool improves your chances as does keeping the tool rest very close to the piece, you will most likely have some chatter marks because of your inability to keep the tool fixed with regard to its cutting orientation rather than because of any small amount of vibration that is occurring in a naturally flexing, but very ridged piece of HSS. I suppose really what I am saying is that I think the vibration within the tool steel that does occur is at a microscopic level and really not as big an issue as the macro level movement of the tool orientation that is inevitable in free hand turning provided you have employed other measures such as limiting tool rest distance in relation to the tool's girth/thickness. I think that any pattern forming on the wood is more likely a function of wood flexing and feed irregularities than tool steel vibration. That is why I wondered about the use of the term vibration because to me vibration is an oscillation from equilibrium about some mean value which I don't believe is necessarily what is happening with the tool orientation itself.

I tend to think along the lines as you do, Matt....

If there is any flexing of the steel, it is microscopic, and won't be of concern to a traditional turner.

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.

Somewhere back in time, I seem to remember a photo of a bent turning tool........in that case, there was one horrible catch!



ooc

 

[Matt Lewis]

Now, I will say that I turn Aluminum all the time for tool handle inserts on my wood lathe with great success, but I have had to tinker with the tool shape, feed and speed and presentation quite a bit to reduce the chatter and effort it takes to keep the tool as rigid as I can by hand. It isn't an easy task, but very doable. The chatter marks are typically easy to clean up with abrasives. I have also turned a limited amount of steel by hand as when making cup centers from steel Jacob's mandrels, turning down washers and turning down nuts. I wouldn't recommend doing it a lot, but it works for small jobs.

 

[john lucas]

Well again I'm not an engineer but let me show you what is happening. I don't know if it's the steel or not, but. I use the tools in the same orientation of cut, both sharpened on the same jig and both have handles identical in length. One makes screeching noises and the other doesn't. That's on the 3/8" detail vs 3/8" spindle gouge. The only difference is the size of the metal. See photos below. You'll notice there is almost no overhang on this tool so the vibration must be a sort of harmonic along the shaft. Could it be my hand moving and not the steel? Sure but I find it hard to believe that I can repeat the cut over and over with the same results. Why would one do it an the other not, unless it's the thickness of the steel.
On the bowl gouge vs detail gouge. Again this is something I've repeated several times with the same results. The bowl gouge can chatter which shows up in the cut while the detail gouge doesn't. In this case there is about 3" of overhang. These 2 tools are both Thompsons made from the same steel with virtually identical handles and both sharpened using the Wolverine jig. These are 1/2". The bowl gouge has a bottom flute thickness of .227" and the detail gouge is .400" It could simply be the summer winter wood harness differences set up a vibration that is seen more by one tool than the other. I don't know but then again. I can repeat the results several times so in my mind that points toward the differences in the steel.

 

[Dale Miner]

I tend to think along the lines as you do, Matt....

If there is any flexing of the steel, it is microscopic, and won't be of concern to a traditional turner.

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.

Somewhere back in time, I seem to remember a photo of a bent turning tool........in that case, there was one horrible catch!

Oldie

ooc

The flex is small, but it is cumulative. Each revolution adds to the surface pattern, and the gouge flexes in more than one direction. As it flexes, the contact between the wood and steel changes, changing the cutting action. The pattern that you can see in the bottom of a deep bowl with a long tool overhang is occurring at a frequency above what our hands and arms can vibrate at. Flexing of the tool, the tool rest, the banjo, and the spindle all contribute to a greater extent than the flabby human elements.

I just went out to the shop, clamped two inches of a 5/8" gouge in my vise, and with a surprisingly small amount of effort,was able to move the handle enough to visibly notice. Not scientific, but noteworthy. I would agree that the least ridgid component is the wood when it comes to vibrations with higher multiples of the rpm, but still think that the tooling and entire system can at times become a factor. The human component is no doubt the weakest part of the system when a one or two times rpm vibration is the problem.





Sharp tools well presented, couldn't agree more.

 

[Odie]

The flex is small, but it is cumulative. Each revolution adds to the surface pattern, and the gouge flexes in more than one direction. As it flexes, the contact between the wood and steel changes, changing the cutting action. The pattern that you can see in the bottom of a deep bowl with a long tool overhang is occurring at a frequency above what our hands and arms can vibrate at. Flexing of the tool, the tool rest, the banjo, and the spindle all contribute to a greater extent than the flabby human elements.

I just went out to the shop, clamped two inches of a 5/8" gouge in my vise, and with a surprisingly small amount of effort,was able to move the handle enough to visibly notice. Not scientific, but noteworthy. I would agree that the least rigid component is the wood when it comes to vibrations with higher multiples of the rpm, but still think that the tooling and entire system can at times become a factor. The human component is no doubt the weakest part of the system when a one or two times rpm vibration is the problem.





Sharp tools well presented, couldn't agree more.

Dale........

Although I hadn't considered this much, I'm inclined to think your hypothesis is true. The only thing that I'd question, is to what degree it applies to us as woodturners. In the case of a captive tool, it would seem it would be more applicable.......I don't have one, and don't do hollow forms, so I'm speaking strictly from a theoretical standpoint with that statement......but, it's certainly more rigid than hand held........

The entire system, rest, banjo, lathe bedways, etc., would have some amount of residual effect, but the truth is that the tool is held by the human element on a fulcrum. Tip goes down, handle responds equally by swinging up......and that handle is in your hands.

I've been giving some thought to your tuning fork example........and, it seems to be an apples and oranges sort of thing, as it applies to woodturning. It's a given that any steel will have a harmonic resonance, but again, this is a matter of degree, and how it applies to woodturning. It does, however, establish that harmonic resonance is fact, and to some degree it undoubtedly does apply to woodturning......the question is when, where, and how much?

I don't know if you are applying the harmonic resonance to those spiraling ridges we sometimes get, but the answer to that (as you have confirmed) is sharp tools presented well.

I have a theory of my own on how those spiraling ridges get started and get increasingly worse. (First and foremost.......this takes a tool that isn't as sharp as it should be.) My theory is that a dull tool will ride the grain's alternating hard and soft spots, on and in-between the annular rings. The tool will cut better where the wood is softer, and worse where the wood is harder. This ultimately causes the tool to rise and fall with the grain, and begins the process of leaving the spiraling ridges. Once the spiraling ridges have started, then the grain of the wood is no longer influencing the tool, but the ridges themselves are. The ridges get increasingly worse as the tool is now riding the ridges. It's only my theory, and I can't guarantee it's true, or not, but as I observe the action at my lathe, it does seem to apply.

The answer is sharp tools presented well, and when I see/feel the spiraling ridges first start to happen......I immediately resharpen.

ooc

 

[Dale Miner]

Odie,

Your assesment at least parrallels the 'cumulative' part of my explanation. You have noticed that the ridges spiral, and are not in straight axial/radial lines. Wheter it is the wood that starts the pattern, or a flex somewhere in the system that does the initial patterning, the next revolution of the wood brings the gouge into contact with that now slightyl higher spot. Flex, bounce, arm movement, or whatever, the next high spot will be slightly later in the revolution and the spiral ridge is formed. The amplitude or size of the ridge will also be increased up to the point that the system can control the formation of the ridge.

Let me bounce this one off you. Doing the bottom of a deep shape bowl with a fingernail ground gouge. Bevel contact is barely possible withoug hitting the side of the bowl. Straight tool rest, about 2.7" overhang. Overall length of tool is 30 inches. Soft maple. Very little early wood/late wood difference in the bottom as most of the cutting is not into the end grain. 750 rpm. Bowl held in a chuck with extra thickness in the tenon. A spiral pattern develops with 18 rigdes. The ridges are .007" valley to peak. 750 rpm x 18 ridges has a frequency of 13500 cpm, or 225 cycles per second. If nothing were flexing, then the end of the handle would have to be moving .070" with the passing of every ridge. At 225 times per second our hand would literally be numb in a short time.

From experience, the above is not an impossibility, especially with a less than fresh edge. I do know that the end of the gouge does not move .070" 225 times per second. It may move that much once or twice per revolution. In the bottom of the bowl with the extra thickness and smaller diameter area, intuitively there is little chance for the wood to be flexing away from the tool to form the ridges. If the handle of the gouge is not moving .070" at each ridge, and the wood is not moving away from the tool .007" at each ridge, then somewhere in the system is a flex that allows the spiral ridges to form. The flex could be in the tool, could be in the tool rest, could be in the spindle assembly, could be in the compressibility of the wood, or in the lathe bed itself. Actually, there is some flex in all the elelments. In the above example, there will be one or two elements that have a harmonic frequency close to the 225 cpm figure. A sharp tool that cuts with only enough bevel pressure to cut the tops of the spirals but not follow the spirals into the valleys flexes the system the least, and will go a long way to cutting down on sandpaper costs. Curved tool rests for short overhangs and gouges ground specifically for deep bowl bottoms; better yet, providing the extra length of the tool rest doesn't become an issue (and it easily can).

I guess it still comes back to sharp tools well presented are best.

 

[John Jordan]

Listen to Dale, he is 100% correct. Tool chatter is not uncommon-that is the steel flexing/rebounding. It may or may not be accompanied by wood chatter. Wood chatter is usually when the wood is thin. The incidence of both can be lessened by the "sharp tool, well presented". Sometimes, though there needs to be more mass in the tool as it is farther off the tool rest. That's why we use larger shafts on hollowing tools as we go deeper, or larger bowl gouges on deeper bowls. And FWIW, there is no difference in the chatter/flex of tool steel vs. plain/mild steel.

I see a lot of less than skilled turners in my classes that get tool chatter/vibrations, and we talk about ways to identify what exactly is happening. Sometimes the chatter is caused by less than a solid connection between the wood/tenon/chuck/faceplate/spindle shoulder. One needs to recognize which of these different elements is the problem.

I know a number of very talented and skilled turners who exploit the tendency of a tool to chatter when extended to cut intentionally cut spirals in the work. And the spirals are indeed caused by the tool flexing, not the growth rings. Spirals are also often the result of simply pushing too hard, and each cut follows what came before, and it gets worse.

And a second FWIW, out of balance pieces, and the shaking and bouncing around of the lathe is not "vibration".

John
____________

 

[Odie]

Odie,

Your assesment at least parrallels the 'cumulative' part of my explanation. You have noticed that the ridges spiral, and are not in straight axial/radial lines. Wheter it is the wood that starts the pattern, or a flex somewhere in the system that does the initial patterning, the next revolution of the wood brings the gouge into contact with that now slightyl higher spot. Flex, bounce, arm movement, or whatever, the next high spot will be slightly later in the revolution and the spiral ridge is formed. The amplitude or size of the ridge will also be increased up to the point that the system can control the formation of the ridge.

Let me bounce this one off you. Doing the bottom of a deep shape bowl with a fingernail ground gouge. Bevel contact is barely possible withoug hitting the side of the bowl. Straight tool rest, about 2.7" overhang. Overall length of tool is 30 inches. Soft maple. Very little early wood/late wood difference in the bottom as most of the cutting is not into the end grain. 750 rpm. Bowl held in a chuck with extra thickness in the tenon. A spiral pattern develops with 18 rigdes. The ridges are .007" valley to peak. 750 rpm x 18 ridges has a frequency of 13500 cpm, or 225 cycles per second. If nothing were flexing, then the end of the handle would have to be moving .070" with the passing of every ridge. At 225 times per second our hand would literally be numb in a short time.

From experience, the above is not an impossibility, especially with a less than fresh edge. I do know that the end of the gouge does not move .070" 225 times per second. It may move that much once or twice per revolution. In the bottom of the bowl with the extra thickness and smaller diameter area, intuitively there is little chance for the wood to be flexing away from the tool to form the ridges. If the handle of the gouge is not moving .070" at each ridge, and the wood is not moving away from the tool .007" at each ridge, then somewhere in the system is a flex that allows the spiral ridges to form. The flex could be in the tool, could be in the tool rest, could be in the spindle assembly, could be in the compressibility of the wood, or in the lathe bed itself. Actually, there is some flex in all the elelments. In the above example, there will be one or two elements that have a harmonic frequency close to the 225 cpm figure. A sharp tool that cuts with only enough bevel pressure to cut the tops of the spirals but not follow the spirals into the valleys flexes the system the least, and will go a long way to cutting down on sandpaper costs. Curved tool rests for short overhangs and gouges ground specifically for deep bowl bottoms; better yet, providing the extra length of the tool rest doesn't become an issue (and it easily can).

I guess it still comes back to sharp tools well presented are best.

Dale......

Was in the shop for the past few hours, and just came in to have something to eat.......

I appreciate your taking the time to give a detailed explanation. I'm sure I'm not the only one who does! When you consider the numbers, it does make a little more sense. 225 times per second is much higher in frequency than I'm feeling through my hands, and that's the point you made that made me reconsider my thinking...........thanks.

Now, all of this is great for discussion, but I seldom get those spiraling ridges anywhere near as often as I did years ago.......and, when I do, I know what to do about it......whether or not I had a proper understanding of the physics!

John J......."vibration" not the best word for out of balance condition.......oscillation would have been the better term, unless there is yet another term that is better.......

Supper done......I'm going back out to the shop!

ooc

 

[hockenbery]

Unless I missed it nobody mentioned the tool rest vibration.
Working on the end of the tool rest more vibration than working over the center post.
When I hollow I try to work over the top of the post as much as possible.

Deep bowl often gets us working on the edge of the tool rest with a lot of gouge overhanging the rest.
Sharp tool, light cuts, short bevel help.

I find the gouge bevel rub increases vibration shortening the bevel by grinding the heel away helps.


Al

 

[john lucas]

Al I was discussing this with Vic from Bestwoodtools one day. He makes his tool rests out of a special steel designed for NASA that is a low vibration steel.
I think that's one of those things that would be hard to tell where the problem is coming from, us, the tools, toolrest, overhang etc. So it's good to try all of it because I'm sure it's a cumulative effect.
I mean who would think that you would get vibration from that huge 12" Powermatic cast iron tool rest. But as you said you can tell a difference when your turning from the end vs the middle. It does depend on the cut your making however. I have a very hard time telling the difference on spindle. Probably because I'm using very sharp tools with no overhang.

 

[MichaelMouse]

Lets see, the tool, the rest - how about the bed? Take your thumb, put it on the rim of your thin wood, and press. See how both it and your flesh compresses? Now try it on that 1/2 cylinder of alloy steel.

Anyone remember the third law?

 

[Richard Jones]

3. A robot must protect its own existence as long as such protection does not conflict with the First or Second Laws.

or........

III. For every action there is an equal and opposite reaction.

Newton was a great ballistician. Also proof that an underhand grip with index finger wrapped offers more control than an overhand grip, for certain things. Gives you that push-me-pull-you not achieved with an overhand grip. Reserved for detailed spindle work only, as you don't want to use up all that mojo at the same pace....... Hey, I could use BOTH grips. Underhand when needed, overhand when needed. What a concept.

Science, you gotta love it.

 

[john lucas]

Well I was photographing a test that our engineering department was doing on setting up some testing apparatus for testing the structure of bridge parts. This was a grant that came in after the bridge collapse a few years back.
They have 20 foot columns buried in the ground that are various thicknesses but none less than 20". Some are steel, some are concrete. They have vibration sensors placed up and down the columns in various locations. They strike the column with a hammer and record vibrations. The sensors are sensitive enough to record you hitting the column with your hand. Now this is a 20" concrete pillar, about that same size on the steel ones. So I'm pretty sure my lathe will vibrate if I hit it with my fist. So I rest my case.

 

[hockenbery]

John,

the earth vibrates too.

So our lathes are vibrating all the time. We just don't notice it.

Al

 

[john lucas]

And the earth is rotating over 1000 miles an hours. I think I need a faceshield

 

[Matt Lewis]

And to think Odie had a rather interesting thread going on this topic. Too bad.

 

[robo hippy]

Hee, Hee, Hee, this got funny.

Vibration comes from all sorts of things.

Ever make a musical/rythmic instrument out of your old school 1 foot rulers and a table of desk top????? Well, hang it out a little bit, and just a thunk, no vibration. Hang it out a bit farther, and you get some twanging. You can move a bit out and back and get different degrees of twanging. Hang it out some more, and you lift the table end off, and get no vibration. There is a range that you can use with little or no vibration. Too far and you get chatter. Farther, and the tool can get yanked out of your hand no matter how big you are.

The wood will vibrate with tool pressure. You can spin a balanced piece of wood pretty fast and it will not vibrate. Most of the tool generated vibrations on the wood are caused by too heavy handed bevel rubbing. Quoting some one, "the bevel should rub the wood, but the wood should not know it". We can use steady rests, either mechanical, or just you hand to dampen the rub. Negative rake scrapers will exert almost no pressure with a gentle touch. When the bowl is getting hollowed out, because there is less solid wood on the other side of the cut, the wood can flex/deform/vibrate. Ever notice how little vibration there is when turning the outside of the bowl?

When you are cutting, as you cut, you get different 'resistance' to the cut as you go through side grain and end grain, also as you cut with the grain and against the grain, some times called up hill and down hill. This is generally minimal, and not really noticeable unless you start really fighting the cut. The more you fight it, the worse it gets, and this is when you get those nice swirly patterns. "Hold the tool as you would a bird. Too tight and you kill it. Too loose and it flies away".

Grain orientation can also allow for some distortion of a bowl at higher speeds as it spins. Minimal at slower speeds and thicker bowl walls, and more at higher speeds and thinner walls.

robo hippy

 

[MichaelMouse]

Well I was photographing a test that our engineering department was doing on setting up some testing apparatus for testing the structure of bridge parts. This was a grant that came in after the bridge collapse a few years back.
They have 20 foot columns buried in the ground that are various thicknesses but none less than 20". Some are steel, some are concrete. They have vibration sensors placed up and down the columns in various locations. They strike the column with a hammer and record vibrations. The sensors are sensitive enough to record you hitting the column with your hand. Now this is a 20" concrete pillar, about that same size on the steel ones. So I'm pretty sure my lathe will vibrate if I hit it with my fist. So I rest my case.

A sonarman can hear a shrimp pass gas at half a mile. Now tell me what the deflection was on those members, and the mechanical advantage at the point of impact, and we'll talk.

 

[john lucas]

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.