Tackling Oversize Lathe Chuck Vibration

Added: 2026-05-12

[00:00:13]Hi everyone, my name is Alex and welcome to an engineer's findings. In this episode, we want to take a look at vibration characteristics of a given lathe and chuck combination and in particularly in case of this oversiz jaw chuck that was given to me a few years ago on this given size MCOV13 lathe here.

[00:00:36]So for the purpose of this video, we go 80 style allin. That means uh we use an 80s style Huelet Packard dynamic signal analyzer. We use an 80s make lathe, 80s make operator, and probably this 70s make chuck here, but nobody knows for sure.

[00:00:59]I guess I should also be wearing some yellow tinted target glasses and smoke some camels, but I have neither of those, so forgive me.

[00:01:08]Well, anyway, story behind this chuck is it was given to me a few years ago and then I made a flange to be able to fit it to the MCOV13 lathe and put it in the storage cabinet and thought to myself, I'm going to be using it every 2 years or so anyway, so nobody cares about the performance of that chuck and the fact that it's oversized for the lathe. Now the problem with fitting an oversized chuck to a given size lathe is that you add a lot of mass cantally levering from the spindle. And the problem with this is that uh I've chucked up some quench and tempered steel here and a parting blade.

[00:01:54]We all know these cases. You can immediately hear it. This setup wants to chatter a lot.

[00:02:00]And the parameters that cause this mostly are the heaviness of the chuck itself and the given size spindle. Now of course we will not increase the spindle size because that is quite infeasible or maybe easier to to just buy a different machine. But what we can do is we can try or at least I want to try how much of an effect we can make by reducing the mass of this chuck by machining away material in strategic locations.

[00:02:32]And thereby how much can we influence the vibration characteristics of this setup with this particular chuck here.

[00:02:40]And when I say I want to machine away material in strategic locations from this chuck, I mean locations that add mass to the chuck but do not contribute a lot to its rigidity.

[00:02:53]And for this purpose, because we want to have a comparison how much of a difference we can make, I have set up this base test here with a chuck in the asis condition.

[00:03:05]And the tone you just heard when we part off a test piece or a test cut, the tone of this vibration, we pick it up with this lavalier mic and analyze the tone in this dynamic signal analyzer. It's an HP 3562 type. And we have to analyze the tone with such an analyzer because the tone itself has a lot of noise added to it like gearbox noise, drivetrain noise and so on. And we have to split apart that tone into all of its subtones and identify just the one that characterizes the bending vibration of this heavy mass that is can delivering from the spindle and we want to improve upon this bending vibration in terms of we want to increase its frequency in engineering terms. Now what does that mean in practical terms? uh we want to increase the pitch of that tone as much as possible. Now why is that good for us machinists?

[00:04:09]Because a higher frequency tends to decay a lot faster and and much easier in such a machine and its cast iron parts than a lower frequency.

[00:04:21]So thereby it's almost a general principle that the higher the frequency the less problems they make in machining setups.

[00:04:38]So the reason for this wiring here on the channel of the microphone is I have to use a source to power the microphone which is done by this PNC wire here. And that allows the microphone to pick up the sound and then transmit it to the instrument. So instrument is going through the calibration and checking itself.

[00:05:02]Tests complete. Nice. So we can set up uh frequency range. Frequency span 1 kilozing mode range channel one range 4 m volts.

[00:05:21]Select trigger channel one input manual with a level of one mill volt.

[00:05:32]Then we want the source to be a fixed sign with source level 0 m volts and a DC offset of 2 volts.

[00:05:51]So then we need an AC coupling of channel one. So then we should be out of the overrange department here. Nice.

[00:06:03]And then we want a dual display. We want the display to a the upper one to be it's filtered input uh sorry uh record over time channel one and we want channel B to be linear spectrum one.

[00:06:33]Yes, that works.

[00:06:37]And I think we are done with the setup.

[00:06:40]Okay.

[00:06:45]So, you have two graphs here. The one is the uh noise over time that the microphone picks up and the lower one is the frequencies that this particular record then is composed of. And we want to select the loudest frequency that is contained in there. And then we most probably have that bending frequency that characterizes this heavy mass delivering from the spindle and vibrating in a bending fashion that way.

[00:07:16]So, let's see what we can gather. I have to arm the instrument every time here.

[00:07:20]So, don't get confused. And keep an eye on that reading up here. These hertz.

[00:07:27]Short interruption here, guys. Sorry.

[00:07:29]When I was filming the scene, I forgot that the number in the top left corner doesn't get refreshed automatically for each new record. So, you have to hit the special marker key button in order to for this to happen.

[00:07:43]So I repeated these measurements and took photos of the readouts and the photos are attached after this scene.

[00:07:51]Let's see.

[00:08:20]So you could see I took several readings or several records and the result which is that that little circle on the highest peak there which is the one tone component of that noise that you here that character or that is created by that particular bending vibration of the chuck on the spindle and the reading up here these 180 htz this is the reading that we compute from the location of that circle here on the horizontal scale so why am I sure that this is the bending vibration well good question let's see what happens to that frequency when we change the speed of the machine. Let's go to a different speed.

[00:09:34]You can see with a different cutting speed, it's also the same vibration, 180 Hz. So that consequently shows us that this is an iggon frequency and I'm pretty sure it's the bending frequency of the chuck on the spindle. So in essence the canty levering uh and pitchfork sort of vibration of that setup here and the cutting forces excite this vibration.

[00:10:01]And here are these readings that I measured afterwards with various spindle speeds.

[00:10:10]So now we have a base reading. Let's see when we modify the chuck how much of an a change we can come up with in regards of this vibration frequency here.

[00:10:21]Now strategic material locations on a chuck. What bull talk is this Alex?

[00:10:27]Yeah, fair point. So what do I mean by that? Now keep in mind we want to improve the vibrational characteristics of this chuck and spindle combination and particularly in uh of its first bending mode which is this mode here forward and back or up and down or a combination of both depending on the cutting conditions here at the tool tip.

[00:10:51]And the most effective way to influence these characteristics is by reducing weight in the areas that overhang the spindle bearings a lot. So this is particularly this face region here. It may have only a tiny fraction of the effect to reduce weight of the flange here in the back because the overhang is much smaller.

[00:11:15]So we want to focus on this face region here. But I don't want to alter anything with the chuck jaws themselves or with their slides or with the bolting pattern. But a place that we may safely use is, if my theory is right, this area here, let's for example machine a big chamfer in this region. And you may have seen the newest rim chucks. They also have a big chamfer in these areas. But only the three chucks, three jaw chucks as I could see. And at first I thought ah it's just to have a place to uh laser on a nice logo.

[00:11:57]But when I thought of this a bit more then it came to me that the intention behind this may be much smarter uh and that is to take away material or mass in areas that are not really required for rigidity of the chuck. And this may be particularly this location here. So let's carefully measure the chuck body on the inside to make sure that we will not collide with the pocket on the inside as we machine away this chamfer in all four locations.

[00:12:26]And then let's see what effect this has on our frequencies in the same cutting conditions as before. Let's do it.

[00:12:36]A word of caution here. Please be advised that changing the structure of rotating parts such as this chuck here, that's dangerous business. And you really have to know what you're doing in order to avoid danger here. These chucks, they're not only loaded with the centrifugal forces, but also with the clamping forces and the cutting forces.

[00:12:56]And those forces flow through the chuck body and thereby stress it a fair bit.

[00:13:01]And let me also mention that I have a solid background in structural engineering and in material science. And consequently, I put a fair bit of thought into this modification before I started. Even if the video may seem like a hack job.

[00:13:17]In fact, if we did a hack job for this modification, we would be risking all sorts of problems. we would be risking danger to the structural integrity of the chuck and we could also introduce imbalance into the machine. Both of which we want to avoid. So in case you're considering any modification along these lines on your equipment, please be careful and please do it in a safe fashion and in a thoughtful manner.

[00:13:42]Thanks.

[00:13:45]All right, so let's disassemble that chuck and take it off of the machine.

[00:13:49]That's also a good opportunity to clean up the um crown wheel on the inside.

[00:13:57]These four bolts I added at some time in the past to increase the stiffness of this setup.

[00:14:03]And this is the flange that I made when I was given this chuck sometime few years ago.

[00:14:11]So the pinions come out quite easily with these two set screws, special set screws. And this is the hold down plate for the crown wheel.

[00:14:22]And after some design work for these chamfers, it's time to put on the rotary table onto the mill.

[00:14:36]So I figured two strap clamps through the slots. They would suffice for holding that part.

[00:14:45]Next, we have to align the axis of the chuck body with the rotary table axis using the D test indicator here.

[00:14:54]That works nicely when the worm drive is disengaged and you can turn everything by hand.

[00:15:04]Next, I'm setting zero angle on the rotary table by setting the uh chuck jaw slides parallel to the X-axis.

[00:15:13]and then move 45° from there.

[00:15:17]So next I have to tilt the vertical milling attachment to the angle as per design for these large chamfers.

[00:15:25]And I'm milling this with the circumference of this I believe 25 mm diameter endmill.

[00:15:32]And at first I was a bit skeptical that this would chatter on me on the final cuts with that long of an engagement length, but it worked out nicely.

[00:15:41]Fortunately, I'm going at 2 mm depth of cuts here.

[00:15:47]That worked nicely. Dry roughing and taking my time here.

[00:15:54]Roughing down quite some material.

[00:16:16]Later on, I had to reset the rotary table. These are the chips I roughed down. Later on, I had to reset the rotary table because of clearance issues and lack of yaxis travel.

[00:16:30]And these are the finishing cuts which I'm doing with cutting oil to get a better surface finish. And I'm also using compressed air to blow away the chips to avoid cutting them twice.

[00:16:48]I'm going a fairly slow speed because uh the the material of that chuck body is heat heat treated steel and it's quite hard.

[00:17:03]So always making sure that things are lubricated and we are not cutting chips twice.

[00:17:15]So the weight of the chuck before and afterwards. So we took down 7 kilos.

[00:17:24]And now let's assemble everything again.

[00:17:26]Making sure that we do not trap any chips or any dirt.

[00:17:31]The hold down ring is not self centering. So it has to be centered with the flange and then tightened. on this particular design.

[00:17:41]Regreasing the pinions and making sure everything is nice and clean and stoned.

[00:17:58]Yeah, I get it.

[00:18:06]Yeah, you may say it's an awkward look of that chuck body now, but I don't care.

[00:18:57]This is making Sure, we have the same cutting conditions that we had before for the measurement.

[00:19:31]Let's try a different speed.

[00:19:34]42. That was 320 RPM. So, let's go to 440.

[00:20:26]So that is 190 Hz in the modified configuration versus roughly 180 Hz that we had before. So that is a five to six% improvement of the vibrational characteristics of this setup here given size lathe with an oversized chuck. And I call this a fair win even if it's just small one but I call this a fair win given the limited amount of material that we took off of the chuck body here.

[00:20:55]Now these this is as far as the numbers are concerned as far as the feel is concerned. The lathe feels a bit smoother and more calm when you operate it with this setup here.

[00:21:06]And a positive side effect of this modification is also that we reduced the rotational inertia of this setup. And thereby we reduce the torque load on the drivetrain and the torque load on the brake of the machine. Before I could more clearly hear for a very short amount of time when you started the spindle in the higher speeds the belt slipping, but now this is smoother and um doesn't give me that much cring much cringe anymore. Even if it's just a short of a kilo that we took off of the setup here.

[00:21:51]Yeah. Also feels nice to the touch and the lighter chuck now handles also better when you're setting up.

[00:21:58]All right, thanks a lot for your interest in this video and staying until the end. I'll see you in the next one.

[00:22:03]Bye.

[00:22:05]And given the limited amount of material there, power failure. there.