ABYMC

[Anon]

There's something wrong with my mill, and I'm not sure what it is.

Here are the symptoms:

-A couple days ago, I turned it on (after a bit change or whatever, so in the middle of work where it was otherwise running fine) and it made a loud growling noise--kind of like the noise it usually makes, just significantly louder. I turned it off and jiggled the gear-change handles back and forth, and the noise went away when I turned it on again. I didn't think much of it at the time--I just figured the gears weren't meshed correctly or something. It made that noise once or twice more over the course of an hour or two's work, but it always went away when I moved the gear handles a bit.

-Today, I was milling for a couple hours and it ran fine. Then, as I was just getting ready to finish, the noise came back and wouldn't go away. I was in the machine's highest gear (1500 RPM) at the time, though I was taking very light cuts. I noticed that the lights were dimming a bit when the noise was present, too--then, after a few seconds, it tripped the circuit breaker. Clearly, there was something causing the motor to draw lots of current--though the RPMs didn't appear to be reduced. I don't have a tachometer, so the speed could fall quite a bit before I'd notice.

I switched the gears back and forth, switched the circuit breaker back on, and it was the same deal. It tripped again, and I couldn't get the noise to go away. The spindle was as freely turning and as noise-free as normal when I spun it by hand.

-Then, I decided to pull the motor and gear train out of the headstock to figure out what the problem was--if there was a burr on a gear or some piece of debris lodged somewhere. This is not a trivial operation on this particular machine, and I'd never pulled it apart before because of this. I pulled the motor and all the gears out, and even without the lower bearing supports in place, the motor and gears ran fine when I applied power. No growling, no dimming lights, no tripped circuit breakers. This rules out any problem in this part of the assembly (as far as I can see), leaving just the spindle assembly.

-I drained the oil to look for any debris. Nothing significant turned up.

-I took the cover off the upper spindle bearing and examined it--it seemed fine (it's not splash lubricated by the gearbox oil, it came pre-greased and is sealed off from that oil). I didn't find any significant debris, though I picked out some small flecks of something brown and relatively hard--maybe some powder-coat primer or something.

-I noticed some slight play in the spindle when I wiggled it by hand, so I decided to measure it. At the bottom of the spindle, I measured 0.0015" (approx.) lateral deflection with maybe a 10-lb pull in opposite directions. I was measuring with a dial indicator that has a resolution of 0.001". At the top, I measured the same way, though it was more difficult to get an accurate reading on the splined shaft. I measured around 0.006" to 0.007" lateral deflection. The spindle ram isn't deflecting--I think almost 100% of this play is in the bearings.

Right now, that's all I know. Even if the play isn't the source of the growling noise, it needs to be fixed for accuracy's sake. I don't see anything obvious that looks like it's for bearing preload adjustment. How is this adjustment normally done?

By the way, the upper bearing looks like it's a normal (non-tapered) roller bearing. I haven't seen the lower one--I think both bearings are factory press-fit in and the lower one is only accessible by disassembling the spindle.

Also, could the play be causing the growling noise and the drastically increased motor load? It doesn't just growl when it's cutting, it does all the time--and it is (or it was) intermittent. I'd think bearing play wouldn't come and go like that.

I'm kind of baffled as to what to do at this point.
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[sylar]

I'd go for the motor first if there isn't any obvious mechanical error.

Give us some details about it, measure the windings to the ground and to each other. Can you measure current input to verify the tags values?

[Anon]

Not easily, but I can set up an ammeter.

My primitive version of an ammeter (are the lights dimming when I turn it on?) says that the motor isn't the problem, because it seems fine when I run it without the rest of the machine attached.
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[Anon]

Update: I put everything back together, and it runs for the moment (I haven't put a load on it yet). I don't know what I did to fix it, if anything. Also, the slop in the spindle seems to be taken up by the splined drive gear. I guess that would imply that that gear is functioning as the bearing preload, whether by design or not I don't know. I think that whatever problem caused it to stop working in the first place is still present, so I suppose I'll see how long it runs before it starts acting up again.
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[metalmaster1766]

the 1st time i heard a growling noise from a machine, it was an O.D/I.D grinder, anyhow it started making a growling noise, i shut it down went and got the boss (owner of the company) and i said WTF is that noise ? he said it sound like a bearing is going in the oil pump,

years later i heard the same type noise coming from a new milling machine, almost like a growling chattering type noise, it is hard to describe, so i go get the boss, and again i say WTF is that noise ? he says its a spindle bearing, machine couldnt have been more than 3 months old, i was the only person that ran it, so we took it apart, checked all the play with indicators and such, not much difference from what you say your readings were

everything looked nice, no metal shavings in the bearings or oil, but we replaced the spindle bearings and it quit making the noise

as for the O.D/I.D grinder, i was told to run it until the bearing goes out completely, 8 years later when i left there, it was still going strong, growling and all, it may still be going to this day, 22 years after i 1st noticed th noise


good luck finding the problem, it may or may not be the spindle bearings, so dont take my word for it

reason i say that is we had a similar problem on another machine and after replacing the bearings and it still made the noise, so it was ok lets replace this, then this, until we found the problem, turns out it wasnt anything, something fell down inside and was rubbing on another moving part, removed the piece of what looked to be an old set screw (never did find out were the screw came from)




Ron


Ron

[Anon]

Spindle bearing was kind of what I was thinking too--it's the only thing that could be making that noise, I think. Except now it's gone away. Hopefully it stays gone, else I may have to do some not-very-fun tinkering. I have half a mind to just machine some plain bearings and put those in there if it goes out completely.

I'll re-measure the spindle play, but it seems to go away almost completely with the splined drive gear on. I guess that's the preload adjustment . . . not something I'd think would be conducive to high tolerance, but this is a cheap import machine. I wonder if the preload (such that it is) wasn't set right from the factory.

Thanks for the reply. It's good to get feedback from someone who's had prior experience with this.
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[machinemaker]

Anon,
I am not sure what type of mill you have, but I know my old bridgeport has made some growling noise before. I think that the noises in my mill were from bad adjustment or too much play between the high and low range mechanism. I had this problem after replacing spindle bearings.
kent
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kent

[Anon]

I have a HF import drill/mill, Central Machinery model ZAY7032G. It's similar, if not identical, to this mill. Part of the problem is that I don't have much in the way of technical drawings, maintenance instructions, etc. The manual available for download is considerably better than the one that shipped with the machine, but it still has nothing useful about bearing preload adjustment.

Here are some pictures, not that they're likely to be particularly helpful:




I'm really hoping that it keeps behaving at least until after I finish the critical machining work on my EV conversion. After that, I'll have more time to dissect it at my leisure, instead of being held up on a time-sensitive project.
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[HWooldridge]

At any appreciable speed, bearings usually howl or knock. In your case, my first thought was the motor but now believe you may have a gear mesh problem based on the fact the growling quits when you play with the gear selectors. Something is touching where it should not so the motor overloads.