Eliminating vibration by fine tuning rpm......

[Odie]

.

(Most all the "old hands" will know this, but I had been thinking of mentioning this for some time......and, now that I'm on vacation, and everyone here is still asleep, I thought I'd give this a shot.......!)

===========================================


If you have a variable speed drive on your lathe, it is extremely helpful to eliminate, or significantly reduce vibration by fine tuning the rpm to match the "harmonics" of your work piece.

In the past, when I was ready to apply cutting tool to workpiece, I simply put my fingers on the bedway with a very delicate touch, turned on the lathe, and adjusted the rpm for the best rpm speed with the least vibrations. This does work very well, but it does require you to acquire a certain amount of refined sensitivity for really nailing it!

There is a better way...........😀

A few years ago, I made up a long adjustable arm for mounting a laser pointer, and positioning it to point the red dot at a specific "trouble" area on a bowl while it was spinning. This adjustable arm was made up from a machinest's magnetic base designed to hold a dial indicator. The original short arms of the base were extended out to a couple of feet for each leg. Anyway, I noticed that the magnetic base was vibrating in tune with what I felt with my fingers on the bedway. I realized this was a method of further refining the harmonics than my fingers were capable of detecting.......and, the new method of fine tuning for vibration was born! (Sometimes, these nice little discoveries just happen by accident, and this is what happened here! 🙂)

For those who would like to try this out, I would imagine any thin wire mounted straight up and solidly attached to your lathe ought to do the trick......you wouldn't have to use the magnetic base, as I have done.

The dial indicator magnetic base with extened arms can be seen here mounted above the headstock on my Woodfast. It extends out through the top of the photo just behind the lampshade of the lamp on the left. It's long and subject to the slightest vibration:
http://www.aawforum.org/photopost/showphoto.php?photo=10105&ppuser=3578


ooc

(Still on vacation, and not using my computer......no spell check here, so bear with me.....thanx! 😱)

.

 

[robo hippy]

I have a Moffat lamp with magnetic base on the headstock of my lathe. With a 2 foot long arm, the slightest vibration of the spinning work will make the lamp bounce. The bounce will be transmitted to the spinning work piece. Most of the time, it is insignificant. It can make a fair difference when you reverse the bowl to turn the inside as well because the tenon/recess will not be true.

However, if you are turning to 1/8 inch thin or less, it can really show up with the rim being noticeably out of round. On my warped bowls. a 3/8 inch thick rim can dry to be 3/8 inch thick on the end grain, and 1/4 inch thick on the side grain.

robo hippy

 

[MichaelMouse]

.
If you have a variable speed drive on your lathe, it is extremely helpful to eliminate, or significantly reduce vibration by fine tuning the rpm to match the "harmonics" of your work piece.

.

Even as a young hand I learned that loading the work with a tool invalidates no load "fine tuning," as the dominant force becomes the difference between high friction upgrain and low friction downgrain cuts. Slower speeds and different feeds fill the needs, not VFDs.

If I reverse a piece and I see any ghost where there should be none, I clean out the mortise. No need to put up with the slightest if you're using a non-destructive hold.

 

[john lucas]

I'll still take variable speed. It's just one more thing you can do along with the proper cutting techniques. My spring pole lathe does have variable speed, (me) however it requires proper cutting technique to get the job done efficiently and cleanly.

 

[Odie]

.

Even as a young hand I learned that loading the work with a tool invalidates no load "fine tuning," as the dominant force becomes the difference between high friction upgrain and low friction downgrain cuts. Slower speeds and different feeds fill the needs, not VFDs.

If I reverse a piece and I see any ghost where there should be none, I clean out the mortise. No need to put up with the slightest if you're using a non-destructive hold.

Hello MM........

Looking at this from your point of view, I feel you have a valid point, considering that you do your turning from a slower speed than I do mine. With this in mind, fine tuning for vibration isn't as important for you at a slower speed, than for me at higher speeds........so, with the understanding that how vibration effects the quality of cut for me, it is something that is more important to my methods of turning, than it would be for yours. Or, that's the way it would seem after contemplating how vibration would apply to the two distinctly different turning styles.

You are also correct that applying tool to wood introduces forces that are not present in a freely rotating piece of wood. There is more force when hogging out wood than from final finish work......and here vibrations would not be as important than for finish work. Here is where I find it necessary to fine tune for vibration. If higher speeds are desired, as they are in my case, it is better to start with the least vibration possible with a freely turning piece of wood, and prior to finish cutting, than to start with vibration that could be eliminated. If tools are sharp, and presentation is correct, then the forces applied to wood is minimal for finish work because the shavings are very fine and delicate.

This is a point where we have disagreed in the past. I still maintain that I get cleaner cuts at higher speeds, so higher speeds are a part of my style. The example I've given in the past is by cutting a piece of paper with a sharp knife at slower speed produces a cut that is less cleanly made than the same sharp knife swiped at the paper at a higher speed. You can buy into that as a valid example, or not.......for me, it makes "horse sense", and can be borne out by practical example at the lathe. I realize there is, as there seems to be on just about everything involving woodturning, those who are opposed in turning philosophy and experience.. I'm trying to avoid "right vs wrong" here, because this discussion of speed and vibration doesn't apply to everyone equally........it only applies to me, and if anyone agrees or not, is not the important thing. Getting the message out there for contemplation and consumption is the main objective........😀

Thanks for the input, MM........ Your post does allow me to make the distinction, as it applies to our differing turning styles.

ooc

.

(I'm now back at home, and back to work tomorrow.......man, that vacation time went fast! 🙁)

.

 

[Ian Thorn]

I can see your point with the knife Odie ,I cut my sand paper with a steel rule from the back of the sheet if the cut is mabe too slow it tears if the cut is fast and at the right angle the paper is cut clean and there is a strip the thickness of the rule as well.

 

[MichaelMouse]

Inertia is what's happening. With the swift cut the paper can't get out of the way. Start a cut slowly while holding the paper taut - works the same.

When the piece supplies the energy rather than the tool, inertia isn't a player. Vice the blade and slide the paper to demonstrate. Then you probably want to remember how that blade did such a good job when the work slid down its edge and why you want the tool and orientation that gives the closest similar presentation when turning.

 

[Odie]

Inertia is what's happening. With the swift cut the paper can't get out of the way. Start a cut slowly while holding the paper taut - works the same.

When the piece supplies the energy rather than the tool, inertia isn't a player. Vice the blade and slide the paper to demonstrate. Then you probably want to remember how that blade did such a good job when the work slid down its edge and why you want the tool and orientation that gives the closest similar presentation when turning.

Good mornin', MM.......

Theoretical discussion is one thing........kind of like discussing the theory of relativity.......open for interpretation with and by examination through different individual levels of mental awareness.

......As opposed to something that can be tested at the lathe through physical application of the theory. In this case, either a better cut can be had by varying the speed.......or, it can't.......and, whatever the result is, it can be had by example! 😀

ooc

 

[Thomas Stegall]

It would seem to me that if inertia is the reason that a quick cut with the knife produces a better cut on paper, than likewise inertia is at play at fast lathe speeds, producing a better cut on the wood for the same reason a better cut happens with the knife (because the wood fibers can't get out of the way).

Odie, when I teach turning, one of the things I mention that you left out in your original post is that lathe speed must change as you turn, because as the mass changes so to does the harmoic resonance of the piece.

 

[Odie]

It would seem to me that if inertia is the reason that a quick cut with the knife produces a better cut on paper, than likewise inertia is at play at fast lathe speeds, producing a better cut on the wood for the same reason a better cut happens with the knife (because the wood fibers can't get out of the way).

Odie, when I teach turning, one of the things I mention that you left out in your original post is that lathe speed must change as you turn, because as the mass changes so to does the harmoic resonance of the piece.

Yes indeed, you are making an excellent point, Thomas.......

Thanks for pointing that out, and it is so noted here........😀

As wood is removed, the harmonics are altered. Lathe speed should change accordingly as progress continues........

ooc

 

[MichaelMouse]

It would seem to me that if inertia is the reason that a quick cut with the knife produces a better cut on paper, than likewise inertia is at play at fast lathe speeds, producing a better cut on the wood for the same reason a better cut happens with the knife (because the wood fibers can't get out of the way).

LOL. I guess you figure "Mach III" isn't just an attempt by Gillette to gain the cachet of fighter A/C, but a basic instruction? That whisker, soft from the shower and the soap has to be attacked quickly. 😉

The reason higher rpm seem to produce a better surface lies in the feed rate. It is effectively slower because the wood comes around more times while the tool travels at a human rate. Depending on presentation, it might be burnished a bit by the bevel or the micro scratch marks from high-pitch will sand the surface to an effectively smaller grit. Makes no difference if you present the tool to allow the wood to cut itself away from the work, as anyone who's ever paid attention when carving or whittling can attest.

Yes, OD, the reason we increase rpm as we transit from the rapid rim to the crawling bottom is to get a smoother cut. Wait - we don't/can't do that (yet) even with the most modern lathe. Wonder why it seems to work fine, regardless?

Oh yes, as far as the magic harmonic goes, you might consider the tool as a fret ....

 

[Thomas Stegall]

That's just the sort or response I have come to expect from you.

Obviously increased feed rate comes with increased rpm's but we were talking about cut quality which applies even when you cut in only one spot without moving your tool along the tool rest. I'm certainly no expert, but as far as the notion that cut quality is never impacted by rpm's, I can think of at least a half dozen or more pro's who have said differently. Rather than the usual intelligent and mutally edifying exchange of thoughts, ideas and experiences that are shared on this forum, perhaps I should list them so you can begin belittling them aswell? 😉

 

[Odie]

I've seen some of MM's natural edge bowls, and from what I can tell, he's getting some pretty good results with slower speeds. I've also seen some of his videos, and they have led me to do some of my own testing of his methods. I have no doubt that by using slower speeds, a turner who practices these techniques can make it work. For my own purposes, I've found that the better, cleaner cut was had by speeding things up a bit.......but, there are so many other things that come into play, that the only way to sum it up is to try it out for yourself. The reader can then make his own judgement as to whether slow speed is going to be right, or not. For MM, it is........ For me, it is not!

Other than the fineness of cut I'm able to achieve with faster lathe rpm, probably the one thing that was more meaningful to me than anything else, is my hand and body movement is much more fluid through the use of the higher speeds that allow for a faster feed rate. In order to get the more artistic shape, or profile I'm looking for, the faster lathe speed does seem to facilitate that fluidity of body and hand movement I wish to have........ For me, body movement does come into play, but not with as much emphasis over what hand and arm movement does. The reason for this, is I tend to concentrate more on overlapping passes than one continuous, long lasting cut through a curve.

I'll have to agree that discussion of Mach III razors, shaving cream, pursuit of fighter jets, and frets on a guitar don't really have much to do with cleanly cutting wood at lathe speeds. Whittling and carving may have some similarities.......but, slower lathe speeds......(even at MM's much slower lathe speeds), are stretching the point a bit......but, of course, that's an opinion on my part. If there is disagreement, I'll read what others would like to say about it, and make an attempt to undersand the point with some benefit of the doubt.......but, as always, I'll decide what I'll accept......or reject!

On these forums, and particularly with some people, it's best to just make your statement, and let it go......give that person the last word. (You probably won't have the last word anyway!) Hopefully, some of the readers will figure out for themselves what is going to work for their own particular needs and purposes........😉 (I wish I could say I always follow my own advice on these things. Sometimes I do, but at other times, I'm just a stubborn old cuss that can't help himself! 😱)

The main point I'd like to stress here.......is to have ALL the information available to those who want to hear from various individual sources, and the methods they use........and for those things to be aired and discussed. Like they say, once that information is out there and absorbed......."the ball is in their court"!



ooc