Vibration when drilling on the lathe

[leehljp]

Today, For the first time, I experienced vibration when drilling on the lathe. I have read occasionally of others in different situations having vibration when drilling on the lathe, but did not have an answer since I had never experienced it. I will admit that I am quite obsessive - that everything be perfect before I drill into a blank.

Today, I needed to make 4 finials for a canopy on a doll bed (repair for a lady to give to her grand daughter). I was a little pressed for time so I cut a 3"x3"x 4" walnut into quarters - 1.5" square by 4 inch. I cut them down to 3 inches long, as that is all I needed. The four 1.5 inch square blocks were not perfectly Square as I was in a hurry and didn't see the need for perfectly square blanks. I really didn't think that was absolutely necessary. For some reason I decided to drill a 5/16" hole first - that I would glue a dowel into the finial, use the dowel to fit through the canopy and into the bed posts. Well, the 1.5 (1 1/2") square blocks were not perfectly square. I put the first block on in a chuck, tightened it and turned it on. My lazy thinking was the drill bit will find the center. BOY Was I wrong. it found the center but turning at 2000rpm and the blank being just a tad out of square, even though tight in the chuck, caused all kinds of vibration. AT first I thought the tail stock was not locked down tight. But it was. It did not vibrate when the drill bit was not drilling, an I am guessing that the weight of the lathe overcame that vibration, but when I put the drill bit into the out of balanced block of wood, the tail stock and head stock fought each other.

For the next finial, I turned it down, centered it and then drilled and did not have a problem. The next two did fine also.

I learned that un-square/not totally centered blanks are being drilled, for me it was enough to cause vibration in drilling on the lathe.

Just wanted to pass along my experience on this.

And just this past week, there was a thread about turning round before drilling. I don't usually do that but I make sure my blanks are square or balanced before drilling. Being round before drilling would do the same thing.

Am I missing something?

 

[robutacion]

Hi Hank,

I doubt that a pen blank out of square would cause vibrations on your lathe unless there is some ware/slack on the lathe shaft either caused by worn out bearings or something else that throws it out of balance and therefore vibrating. I don't recall what lathe you've got but even the smallest of lathes shouldn't vibrate from an out of square small piece of wood such as a pen blank.

I believe you have a problem on that lathe that is probably caused by metal fatigue of some sort, I may be wrong but I don't think the problem will go away that easy, these are my thoughts...!

Cheers
George

 

[JimB]

If I understand what you did correctly you mounted non-square 'square' blanks in your chuck. That was probably your problem. When you mount square into a chuck you have 8 points of contact of jaws and wood. When the wood isn't square you will have fewer points of contact and less stability.

 

[TonyL]

This was my experience (s):
Blank cantered in chuck
Forgot to tighter TS.
Had ram partially ejected

 

[magpens]

Hank, I always round the blanks .... and square the ends .... before drilling on the lathe.

They need to be rounded in order to be properly gripped, as Jim says above ... and also to make them symmetric ... which makes for good balance.

And then I square the ends. . If you don't do the squaring, it is easy for the tip of the drill bit to wander off center. . Start the hole with a center drill.

Even after squaring, I am extremely careful during the start of drilling .... take it very slowly until the hole is 1/2" deep.

Whatever the blank material, I follow this procedure.

 

[Charlie_W]

In addition to previous comments, the bit may have wandered off axis following softer grain. This could cause vibration.
Sharp bits, center bit, slow feed.......and sometimes a bit will still wander.

 

[jttheclockman]

You do not need perfectly square blanks to turn on a lathe to drill without vibration. It is how they are mounted. That is why I like the pen jaws. They grab 2 points opposite each other. I drill unsquare blanks all the time. Granted they are not huge logs but non the less they are wider on 2 sides that the other 2. The blank still turns on center if properly mounted. I believe that is where your problem came in.

 

[leehljp]

If I understand what you did correctly you mounted non-square 'square' blanks in your chuck. That was probably your problem. When you mount square into a chuck you have 8 points of contact of jaws and wood. When the wood isn't square you will have fewer points of contact and less stability.

Yes, that is what I surmised. I have always been obsessive about squaring for 8 points of contact. But this time I didn't. I often do what Mal said too - round off an end and then reverse it similar to making a tenon (round) and then turning from a grip on the tenon.

Mal, I too, often round and end off and then reverse it for a perfect grip.

Charlie, I agree that softer grain can cause that, and walnut generally has some softer grain.

By the way, I double checked when it started vibrating. My first thought was I didn't tighten the tail stock down, but it was; then I thought the drill chuck was loose, but it wasn't.

A single tire out of balance can shake the whole car, and at certain speeds it is not noticeable, but at certain speeds, it shakes.

JohnT, I agree. I have not had problems in the past. Today, I rushed it. "its how they are mounted". I had a hunch I was rushing it and I just mounted it quickly in a way so that it was not in perfect contact with the jaws. I thought enough pressure (tightness) would be fine. It wasn't.

George, I was using my Grizzly G0462 - 16 - 42. I have a Rikon that I do most pens on.

You guys are providing some good information to link to when others run into this. Thanks

 

[Dalecamino]

Just a thought Hank. Could it be time to sharpen the bit? It just seems to me, the blades might be skipping before they start cutting. I could be wrong!

 

[monophoto]

Regardless of whether the blank was square, it has an axis of rotation. My suspicion is that the drill bit was not centered on that axis of rotation.
It's true that a bit will 'find a center', but that center isn't necessarily on the axis of rotation, especially if the tail stock isn't lined up with the headstock exactly. The is very possible, if not likely, on lathes where the tailstock can rotate slightly before it is locked down to the bedways.

The approach I take to minimize this concern is to find the true center of the blank after it is mounted and rotating - use a skew to cut a dimple at that center. Then, I extend the tail stock ram until I am sure that the morse taper on the jacobs chuck is fully engaged (on my lathe, that means extending the ram until I get to the engravings that show the length of extension - anything short of that and the chuck taper may be loose) - and finally slide the tailstock toward the workpiece to align the tip of the bit to the dimple in the workpiece before locking the tailstock down to the bedways.

If the bit isn't properly centered, there will be vibration, and the bit may flex. I frequently use small diameter long (aircraft style) bits, and have learned the hard way that repeated flexing can cause metal fatique that can break a bit.

 

[JimB]

You didn't mention what type of jaws you have on your chuck. Dovetail jaws are NOT good for gripping square stock.

 

[leehljp]

Regardless of whether the blank was square, it has an axis of rotation. My suspicion is that the drill bit was not centered on that axis of rotation.
It's true that a bit will 'find a center', but that center isn't necessarily on the axis of rotation, especially if the tail stock isn't lined up with the headstock exactly. The is very possible, if not likely, on lathes where the tailstock can rotate slightly before it is locked down to the bedways.

The approach I take to minimize this concern is to find the true center of the blank after it is mounted and rotating - use a skew to cut a dimple at that center. Then, I extend the tail stock ram until I am sure that the morse taper on the jacobs chuck is fully engaged (on my lathe, that means extending the ram until I get to the engravings that show the length of extension - anything short of that and the chuck taper may be loose) - and finally slide the tailstock toward the workpiece to align the tip of the bit to the dimple in the workpiece before locking the tailstock down to the bedways.

If the bit isn't properly centered, there will be vibration, and the bit may flex. I frequently use small diameter long (aircraft style) bits, and have learned the hard way that repeated flexing can cause metal fatique that can break a bit.

Louie, I played this idea over and over in my mind last night. Your first paragraph is what I visualized mentally in replaying the problem. But I did check that everything was locked down immediately. It started off in the central axis of rotation. I did not mark the center, because It did not matter - since the blank was 1.5" square and I only needed a finished finial at 1" diameter.

After all of my thinking and visualizing, I have a sneaking suspicion that the blank "moved" a portion of a fraction of an inch in the chuck as the bit began entering the blank. Going back to others perception above, when all the jaws of the chuck are not equal in force upon a blank, there is potential for movement. When minuscule vibration or forces (from a drill bit beginning its cutting) other unequal grasps/holding points will/can change. My conclusion in replaying the event is this: When forces are not equal in holding a blank, even if it is tight, the potential for vibration increase, and the pressure from a bit beginning its cut, while everything is moving, increases chances for alignment issues that introduce vibration. I do tighten it down to what I consider tight and the "teeth" marks of the chuck jaws are evident. But in wood, there is always some give, which is not good.

I am going to try and re-create the vibration problem today just to see if I can.

 

[leehljp]

You didn't mention what type of jaws you have on your chuck. Dovetail jaws are NOT good for gripping square stock.

I was using the 4 pin jaw like theses of PennState

#1 Pin Jaws

Pin style replacement Jaws inserts into 1 opening. Compatible with all C style chucks including: CMG3C, CUG3418C, CSC2000C, CSC3000C, CSC3000CTN

www.pennstateind.com

 

[jttheclockman]

Hank just think of a log on a lathe being turned round. The vibration is tremendous because of off balance. As that log is rounded and reduced to more stable weight the vibration lessens. Even though there is a center of axis as mentioned that vibration can and will throw that center off somewhat. Now your situation is less dramatic but same principle. The vibration was from the chuck to headstock area.

 

[Charlie_W]

I have found some brad point bits in which the point is not centered in the bit. This can cause drilling issues right off the bat.
Not I rarely use the Brad point bits.

 

[leehljp]

Just as I was getting ready to do some checking on the vibration on the lathe, LOML decided I needed to put out more Christmas decorations (all day) because we will have all 10 grandkids here (at different times) the week of Christmas, and two at the end of next week.

BTW, I did mention above that for the last three, I did not have the problem because I change my technique. Technique IS important. I don't have any percentages, but there certainly seems to be one technique that results in less problems than the other, or others.

 

[mmayo]

I too think I have far better luck with pen blanks or stoppers that I took the time to be sure they were square. My two cents, that's all.

 

[Curly]

Vibration is sometimes a function of harmonics. One small vibration synchronizing with another, amplifying and causing another. Now I think you might have been drilling too fast and slowing the RPMs down might have been all you needed to do.

I don't buy the chuck clamping arguments. I used to watch my father hold chair stretchers with the tenon broken off, in his left hand while turning the tailstock wheel, drill bit chucked in the headstock, to drill a hole for a dowel repair. I've done it myself and there is no chatter or vibration. That's why I think you should slow the lathe down to 500 RPM or so. The only time I would be drilling at 2,000 RPM would be if it was a little bit like 1/8" or less.

Pete

 

[LK&T]

I was gonna mention harmonics, and Curly beat me to it. I have some experience with this and learned some of the basics in music classes and, strangely, helicopter maintenance. Unless you had something grossly out of whack, I believe you had one or maybe two little things off a bit. These small things got together and through dumb luck you set up a condition where you created a vibration that matched something else's harmonic frequency. Most every thing has an inherent harmonic frequency that it'll vibrate at if struck. If an outside source creates the same frequency, the object will readily vibrate at that frequency and, under the right conditions, vibrate at a much higher amplitude! I think this is what happened on your lathe. If I'm right, it should be difficult to replicate. If you can easily replicate the vibration, I'd definitely start checking for problems.

 

[leehljp]

Harmonics is something I haven't seen mentioned in the past, but it did cross my mind - I know that harmonics is a real force. It crossed my mind the instance the vibration started and just after everything was turning smoothly, but I dismissed it almost instantly with the thinking of loose tail stock, which I immediately checked after stopping the lathe, - it wasn't a loose tail stock. After shutting down, I grabbed the tail stock drill chuck to see if I could move it or shake it (was it loose?) I could not. Same for head stock chuck. Tight. Alignment was perfect.

(By the way, Nikola Tesla loved playing with harmonics and caused a few minor earthquakes when he experimented with the harmonics of a building or two. Very interesting subject.)

Getting back to my thoughts at the moment was the headstock chuck grip on the block. A three sided firm grip on a 4 jaw chuck (all 4 are in contact) leaves one side more loose than the other, which makes it susceptible to movement with a sudden force applied from another direction, and makes harmonic more relevant. Pete, I don't doubt that your dad could do that. Some people have an innate ability to do those things and know how to compensate on the fly. I have watched master woodworkers drill by hand precise angles that most people could not drill that accurately with guides. Even harmonics can be changed with minor adjustments of a hand grip at the right place. And that itself plays into the idea of the thoughts on a 4 jaw chuck griping a non square block unequally.

I remember reading a few times in the past on this same subject - of someone who has been on this forum a good while, but I forget who it was - that he will grip firmly the tail stock at the chuck (it is not turning) as he drills to keep the vibration down. With the hand on the tail stock drill chuck, one can "feel" when vibration is just starting and compensate in several ways - slowing down the feed rate, pulling the bit back out a tad, tightening the grip which will dampen the vibration (change the harmonics too), and even changing the speed which would definitely change the harmonic frequency.

I do think I should have dialed the speed down to 550, the slowest I can get mine to go.

Thanks for the input.

 

[Curly]

LK&T I got a good deal of my understanding, limited as it is, as an fixed wing mechanic.

Hank my point was that the chuck was gripping things tight enough and it was other things in play. Drill bit a little dull or the cutting edges not even, feeding a little too slow or unevenly so the bit isn't always engaged the same, the density of the wood (late growth/early growth) rings varying the engagement of the cutting edges can all create chatter and vibration, plus of course the speed. Even if you duplicated everything again you might not set up the harmonics because the growth rings are different in the new piece of wood. It is hard to know exactly but we can understand the factors that cause it, hopefully working in a fashion that prevents it.

Some of the penturners turning antler use pliers to hold the antler while using the tailstock to advance it into the drill bit chucked in the headstock. It lets them pick the best line through the uneven shaped material. Same basic idea as my father used.

Pete

 

[monophoto]

I don't disagree with the concept of harmonics as a contributor to the problem Hank reported, but I'm hesitant to identify that as the 'cause' for two reasons.

First, for harmonic resonance (which is the exact term for this phenomenon) to occur, there must be a source of excitation. That is, the effect of harmonic resonance is to amplify the magnitude of vibrations, but there must an underlying source of excitation. Harmonic resonance can make vibrations worse, but it doesn't necessarily trigger vibrations.

Second, there is the principle first stated by William of Occam, aka Occam's Razor, which states that the simplest explanation is usually the best explanation. Harmonic resonance is a good explanation, but only after other things have been ruled out.

Which leads me to say that I still think the core problem here was that the drill bit wasn't properly centered - either because it 'found a center' that wasn't on the axis of rotation, or because the axis of rotation shifted when the blank moved in the chuck.

Incidentally, Hank's idea of resting the left hand on the drill chuck is excellent for several reasons. It makes it possible to sense vibrations when they are small and less likely to cause problems and when there is still an opportunity to do something about them, and it provides additional damping to reduce the magnitude of those vibrations. And of course the classic explanation that the jacobs chuck is held in the tailstock via a morse taper, and holding it with the left hand means that it is possible to keep it there when the bit is withdrawn from the workpiece.

 

[leehljp]

LK&T I got a good deal of my understanding, limited as it is, as an fixed wing mechanic.

Hank my point was that the chuck was gripping things tight enough and it was other things in play. Drill bit a little dull or the cutting edges not even, feeding a little too slow or unevenly so the bit isn't always engaged the same, the density of the wood (late growth/early growth) rings varying the engagement of the cutting edges can all create chatter and vibration, plus of course the speed. Even if you duplicated everything again you might not set up the harmonics because the growth rings are different in the new piece of wood. It is hard to know exactly but we can understand the factors that cause it, hopefully working in a fashion that prevents it.

Some of the penturners turning antler use pliers to hold the antler while using the tailstock to advance it into the drill bit chucked in the headstock. It lets them pick the best line through the uneven shaped material. Same basic idea as my father used.

Pete

Pete, you are right, I may not be able to duplicate it. But it was interesting.

I am going to forego the rush to get things done and keep to my normal technique in the future. I would not have even posted this thread if I had done the correct technique (for me) to begin with.

Which leads me to say that I still think the core problem here was that the drill bit wasn't properly centered - either because it 'found a center' that wasn't on the axis of rotation, or because the axis of rotation shifted when the blank moved in the chuck.

Louie,
This is what I want to check when I get my into my shop. I have a couple of the "un-square" blocks left and I want to see what is happening. I am curious like that.

My countryboy logic wants to know: Why does a scraper or gouge on the edge of an un-square block turn it round, but a bit stuck in the center causes a ruckus?

You want to know what an un-round drive shaft will do to a car?
Back when I was in college, I had a muffler that had a hole in it and it sounded good, but I ordered a muffler from the automotive parts store. I had not yet put it on, ad needed to go down a dirt road to where the farm tractor was. The dirt road had lots of clods from the tractor being on it just after it rained. The clods were dry and bigger than two fists. My 4 year old 66 chevy Impala was rear wheel drive that had the drive shaft hump - that you older guys are familiar with. Well, I hit a clod, it knocked the muffler off, it hit the ground, jumped up between the drive shaft and rear hump; it widened the hump by 6 inches, forced the drive shaft out of round (bent it) There was a terrible shaking as the drive shaft twisted, pulled the transmission in half and all of it went out the back end before the car came to a stop.

Out of balance is a terrible (and sometimes costly) thing!

 

[peter1958]

Today, For the first time, I experienced vibration when drilling on the lathe. I have read occasionally of others in different situations having vibration when drilling on the lathe, but did not have an answer since I had never experienced it. I will admit that I am quite obsessive - that everything be perfect before I drill into a blank.

Today, I needed to make 4 finials for a canopy on a doll bed (repair for a lady to give to her grand daughter). I was a little pressed for time so I cut a 3"x3"x 4" walnut into quarters - 1.5" square by 4 inch. I cut them down to 3 inches long, as that is all I needed. The four 1.5 inch square blocks were not perfectly Square as I was in a hurry and didn't see the need for perfectly square blanks. I really didn't think that was absolutely necessary. For some reason I decided to drill a 5/16" hole first - that I would glue a dowel into the finial, use the dowel to fit through the canopy and into the bed posts. Well, the 1.5 (1 1/2") square blocks were not perfectly square. I put the first block on in a chuck, tightened it and turned it on. My lazy thinking was the drill bit will find the center. BOY Was I wrong. it found the center but turning at 2000rpm and the blank being just a tad out of square, even though tight in the chuck, caused all kinds of vibration. AT first I thought the tail stock was not locked down tight. But it was. It did not vibrate when the drill bit was not drilling, an I am guessing that the weight of the lathe overcame that vibration, but when I put the drill bit into the out of balanced block of wood, the tail stock and head stock fought each other.

For the next finial, I turned it down, centered it and then drilled and did not have a problem. The next two did fine also.

I learned that un-square/not totally centered blanks are being drilled, for me it was enough to cause vibration in drilling on the lathe.

Just wanted to pass along my experience on this.

And just this past week, there was a thread about turning round before drilling. I don't usually do that but I make sure my blanks are square or balanced before drilling. Being round before drilling would do the same thing.

Am I missing something?

I had the same problems and didn't think aboout it coming from unsquare blanks, but i discovered that if you put them in a 4-jaw chuck with the jaws on the sides of the blanks, 2 jaws don't touch the wood at all.
Now i put the corners of the blank against the jaws, and all 4 jaws clamp the blank.
The 4 sides must be parallel and have roughly 90 degrees corners so the jaws can touch easily all corners.
Now i make more work of it, all blanks are square within 0.5 mm 0.02 inch. But stil clamp on the corners.
Try it, maybe it is helping.