Spindle Harmonic?

I’ve just recently started getting a rather odd effect. My spindle seems to be either going harmonic, or going out of balance, I’m not quite sure which. It runs quite smoothly with no bit in it, but putting a bit in it seems to sometimes cause very odd vibrations, and sometimes not. I’ve tried bits ranging from a 1.5" long 1/4" diameter V-bit, to a 3" long four-flute quarter-inch endmill, and it seems to be VERY random. I’ve checked all of my V-wheels, the tightness of my spindle in the carriage, the tightness of every screw on the darn thing… I can find no reason at all that this should be building up such a vicious vibration just spinning free in air! To the extent that I have to immediately shut the spindle down, because the bit is visibly vibrating at the tip through perhaps .020 of oscillation! The noise is horrible, and the vibration is worse.

I know the bits are good, because they’re largely the same bits I’ve been using since I got the unit. I have been able to continue running by installing and re-installing the bit until the vibration is minimal, but it’s still there… Something isn’t quite right here. I’m not terribly worried because I’ve got the mount for my DeWalt showing up next week some time, but I’d like to be able to keep it running until it shows up, and I’m starting to be afraid for the longevity of my Z-axis with that kind of vibration building up.

What else should I check here? I’m somewhat at a loss!

Just curious if you’ve checked the collet for anything in it? I bet you probably already have, but just in case, make sure the collet and nut are clean before each job, or at least after every tool change.

If you go to a liver doctor he’ll tell you you have a liver problem…
If you go to a heart doctor, he’ll tell you you have a heart problem…
If you go to an accountant, he’ll tell you you have too many expenses…

I actually design machines for a living (mostly large conveyors) and I sell repair parts for them; I sell MANY bearings. So guess what? I’m gonna say you have a bearing problem!

Given you have a vibration and all your “mounts” are tight, then I can only conclude you have a bad bearing in the Spindle. I’m not sure if the Spindle incorporates “ball bearings,” but you are definitely giving the signs of a broken “ball retainer.”

The “ball retainer” is a metal or plastic part inside the bearing that holds the balls at equal distance around the inner race. When it breaks, it allow the balls on either side of the break to separate and create a “gap” that the inner race can move into. We are talking on a microscopic scale here: maybe .00001 - .00005 or so inside the bearing.

The reason you are not experiencing this problem with an empty collet is that the forces on the balls are equal in all directions (centrifugal force) - I.e.: nothing is “pushing” on the balls to make them separate. The moment you put a bit in it, you have SOME “radial” load (the shaft is pushing outward from it’s axis of rotation). This load WILL find that broken retainer and separate the balls allowing for misalignment of the inner race and subsequently, the spindle shaft. Voila! Vibration (and heat, but we’ll cover that demon later)!

…and if the Spindle has Bronze “sleeve” bearings, then you could have “wiped” one. That is, you have created a flat spot or an area where it is no longer “round” and the shaft is able to walk around.

A TINY bit of misalignment in the bearings will create a huge defection at the end of the shaft (in this case, your tool bit).

One last dark cloud: If it is a broken ball retainer, WHEN it fails completely, it will be EPIC (on a tiny scale to us large humans)! The retainer will jam between the balls and the races and bring it to an immediate halt - if you are lucky… if you are not lucky, it will just SLIGHTLY jam-up creating heat from the friction and catch the dust on fire - seen this MANNNNYYYYYY times in little redneck factories where they make pallets or lumber…

This advice is worth exactly what you paid for it…


I enjoyed reading your reply Jay, thank you

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I have noticed that in the last few days the runout at the tip of the bit has increased significantly. I was just stating to worry about the lower bearing, then I read your post. Now I am really worried.

I should probably order the Dewalt 611 mount, I have a feeling I may need it soon.

I have indeed checked the collet, @sketch42, and it’s clean as far as I can tell! No chunks in the grooves, the surfaces are clean, and the surface inside the spindle is clean as well. That was actually one of my first thoughts, but unfortunately…

I’m thinking that a bearing dying is definitely possible, although I have no idea what these spindles use bearing-wise to begin with. It’s odd, though, that there’s no squeal or any of the other usual ‘dying bearing’ noises that you might expect to hear. It runs just fine sound-wise, until that vibration builds up!

From what I’ve heard, the DeWalt turns it into an entirely new machine anyway, so probably a good idea to upgrade if you’re getting some weird performance issues anyway, @AllenMassey. I’m really looking forward to getting mine, for sure.

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My wife is already complaining about the noise from the 300w quiet spindle, how much louder is the 611?

I may need to build an enclosure.

It’s a lot louder than the 300W spindle as stock, but not that much louder than the shop vac I use for dust collection anyway. An enclosure might be a good plan, That’s going to be one of my next major projects, I think. I really need a truly flat surface to set this up on! I’m actually pondering discarding the wasteboard support rails and all that mess entirely, and just mounting the x-carve directly to the table, using a drop-in wasteboard surface that’s held down by a pair of toggle clamps or something in the corners.

Hmm, the problem is definitely increasing, I think I’m actually going to have to stop using my X-Carve until I get the new mount in. Even with a 1/4" diameter 60-degree v-bit, I’m getting some fairly severe vibration now, sufficient that things are moving around on the table near the X-Carve. I’m afraid of causing damage with that much vibration, so I think it’s time to shut down for a couple days until I can get the DeWalt mounted.

These cheap Chinese spindles really seem to suck, there are a LOT of people on here that seem to be having various problems with them!

I understand this is old. But I’m having this issue and not finding much about it. Was the bearing your issue?

Check your spindle to very closely to see if it’s cracked.

Sorry. Couldn’t resist a Fletch reference …