I've forgotten Peter, do you have an iPhone or an android? If you have an android, I can recommend some apps that I like and use for things like this and "other life's puzzles" !!!!
If you have an apple, you are on your own..... LOL!
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Cyclical Mill Vibration & Power Discussion
- Thread starter PeterT
- Start date
I've forgotten Peter, do you have an iPhone or an android? If you have an android, I can recommend some apps that I like and use for things like this and "other life's puzzles" !!!!
If you have an apple, you are on your own..... LOL!
slow-poke
Ultra Member
An oscilloscope would not be particularly useful to evaluate this problem.
The correct tool for this is a power quality meter/recorder. We designed and sold them in large quantities to PG&E. Power utilities have these and if you complain they might come out and leave one for a week so they can assess.
In general the power system frequency changes very very slowly +/-0.05Hz, but typically less and is corrected at the end of the day to keep the synchronous clocks on time. The entire grid and all the direct connected synchronous motors are in sync so it's not possible to have the frequency wandering in one part of the grid relative to the grid. Actually motor speed will vary with load/slip but typically about 50RPM for a 4 pole motor.
Voltage does vary all the time and by much more than frequency.
www.fluke.com
The correct tool for this is a power quality meter/recorder. We designed and sold them in large quantities to PG&E. Power utilities have these and if you complain they might come out and leave one for a week so they can assess.
In general the power system frequency changes very very slowly +/-0.05Hz, but typically less and is corrected at the end of the day to keep the synchronous clocks on time. The entire grid and all the direct connected synchronous motors are in sync so it's not possible to have the frequency wandering in one part of the grid relative to the grid. Actually motor speed will vary with load/slip but typically about 50RPM for a 4 pole motor.
Voltage does vary all the time and by much more than frequency.
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So if its unlikely to be electrical, I'm thinking the likely culprit is vibration at the machine's structure's natural frequency. Can you change motor speed easily or take the belt, even the take the pulley off ..... things that might cause the vibration
Re oscilloscopes, I picked one of these up the other day, was up for $117 and caught my ere. I've got the usually suspects on the bench, but a handheld one for close to $100 delivered? Wow. Now I just have to think of something to use it for lol
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Re oscilloscopes, I picked one of these up the other day, was up for $117 and caught my ere. I've got the usually suspects on the bench, but a handheld one for close to $100 delivered? Wow. Now I just have to think of something to use it for lol
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historicalarms
Ultra Member
You can search vibrations & noise in a mechanical issue with a stethoscope very easily . A very inexpensive "usable in a pinch" stethoscope is simply a thin dowel of wood (in one instance where nothing else was immediately handy i use a surveyors lath to find a slight tick in a 500 hp engine). Touch the wood to your ear and touch the other end to various parts of your machine, you will easily tell when you are closer or further from any noise.
I'm quite surprised by that comment. I agree that you won't be able to see frequency shifts. Even if they occur, they are very low level as you pointed out. But voltage changes, cycle anomalies, and noise ought to be easy to see if they happen as often as Peter suggests.
@PeterT - I have to say that I doubt your issue is power quality. None-the-less, sometimes you just have to check.
I think that voltage changes, system noise, and cycle anomalies should be easy to see unless they are very sporadic. To see sporadic changes, you have to be watching when they happen - hence one of the many values of power quality monitor recorders. But it sounds like your problem is pretty usual / routine. Therefore, I would have thought a scope would rather easily show major voltage and noise issues if they are present. And for what it's worth, I don't think minor frequency shifts of the type that can occur on the grid would cause the problems you are experiencing. As SlowPoke says, they are very very minor - tiny fractions of a percent - that have to get corrected every so often anyway. It's not that it can't happen, it's more like it just doesn't happen! The grid won't allow it.
@PeterT - small suggestion, check to see who else shares your pole transformer. This would help narrow down the possible culprits - assuming it isn't you.
Also, if you have a way of monitoring your instantaneous home power consumption, you can sometimes isolate a problem just by throwing breakers. It's amazing what a bad fridge, freezer, air conditioner, sump pump, welder, etc can sometimes do to your home power quality.
I throw all these ideas at you because you asked. But as I said above, I think your culprit is not power quality. I think it's much more likely that you have a mechanical problem like a natural frequency or harmonics of some kind. If you can hear changes that are reliably reproducable, a frequency analyser should be really useful.
BaitMaster
Ultra Member
Hey man, come over here for a minute. You ever heard of a VFD?
BaitMaster
Ultra Member
Asynchronous motor. Synchronous motors don’t have slip…..
If you like, I could fix it for you. Your call if it's worth it.
> do you have an iPhone or an android?
Strange as it may appear, Apple. I'm not a power user. Its familiarity laziness syndrome.
>A very inexpensive "usable in a pinch" stethoscope is simply a thin dowel of wood
yes that's what I was referring to with the 'screwdriver test'. Metal blade on bearing cap, plastic handle to ear. It works amazingly well. I think mechanics have something more sophisticated that can touch or focus? That would be useful. But I really like the strobe 'freeze frame' idea to put to rest that its not a resonance that the belt does a funky flap or the spring does a funky slinky motion
>You ever heard of a VFD?
Oh ya, trust me, I have 'friends' LOL. And I'm aware of the advantages. In that scenario the red chunk gets replaced with a rather specific & not inexpensive 3-phase motor, plus a new black box on the wall. But if the current resonance is inside the green chunk regardless of what spins it, then I'm no further ahead. Now running the motor detached from mill on the ground was the first test completed to isolate 'obvious' motor problems. Nothing out of the ordinary discovered there, very smooth. No audible low resonance in & out of any kind, just constant motor hum. So onto the green stuff we went. Now motor could be further torn down, requiring spring/plate removal & some more effort but gut feel is probably OK. Now that capacitor issue has me wondering but because its the original. any comments there?
Strange as it may appear, Apple. I'm not a power user. Its familiarity laziness syndrome.
>A very inexpensive "usable in a pinch" stethoscope is simply a thin dowel of wood
yes that's what I was referring to with the 'screwdriver test'. Metal blade on bearing cap, plastic handle to ear. It works amazingly well. I think mechanics have something more sophisticated that can touch or focus? That would be useful. But I really like the strobe 'freeze frame' idea to put to rest that its not a resonance that the belt does a funky flap or the spring does a funky slinky motion
>You ever heard of a VFD?
Oh ya, trust me, I have 'friends' LOL. And I'm aware of the advantages. In that scenario the red chunk gets replaced with a rather specific & not inexpensive 3-phase motor, plus a new black box on the wall. But if the current resonance is inside the green chunk regardless of what spins it, then I'm no further ahead. Now running the motor detached from mill on the ground was the first test completed to isolate 'obvious' motor problems. Nothing out of the ordinary discovered there, very smooth. No audible low resonance in & out of any kind, just constant motor hum. So onto the green stuff we went. Now motor could be further torn down, requiring spring/plate removal & some more effort but gut feel is probably OK. Now that capacitor issue has me wondering but because its the original. any comments there?
Yes, been to the bottom of the head. I haven't done a detailed writeup yet but some picture samples. The loose-'ish' bearing I was referring to is within this gear shaft assembly. It was pressed out & replaced & the minor looseness fully eliminated. All bearings replaced even though they felt fine. Drive belt was replaced because it appeared to be running a bit low = possibly stretched (later determined perfectly normal. Main speed change belt in new condition. No wear, no cracks. Very minor belt dust in head. Lubrication perfect. Its practically minty condition.
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ChazzC
Ultra Member
I've had the meter plugged in for the last 35+ years (yes, potentially overloaded receptacle, but with the exception of the meter & emergency light – pointed to illuminate the lathe & mill, just in case – none of the other loads are simultaneous):
One day I noticed an intermittent hum coming from the breaker panel that was in time with the voltage swinging from just under 115V – just over 125V, so technically within range, but this was about 1Hz. After checking with the power company (yes, back then you could call, get transferred to a technician and actually tak with them), and was advised to check the connections, particularly since the incoming power was via Aluminum conductors. Donning my electrical gloves and cotton over-gloves (to keep from puncturing the rubber liner) and using insulated tools I torqued all of the breaker connections, including the mains: no change. I call the guy back (he gave me his direct extension!), and he said he'd look into it. He called back a few days later and asked if the problem went away: I checked and everything seemed OK. Apparently there was a problem on the high voltage side of the underground lines about a mile and they were getting a phase imbalance; they replaced a transformer and all was well.
Something similar may be happening to @PeterT : voltage and frequency swings.
I have one of it's big brothers FNIRSI 1014D and its little brother the FNIRSI TSO-TC3. Amazing tools for the cost. I've not found any shortage of places to use them. Way easier than dragging out one of my Tectronix scopes, and less pucker factor when you are looking at unknown signals too! For me, the nicest feature of the TC3 is transistor terminal identification.
Well, there are lots of ideas and suggestions, so I will throw a couple into the pot too. A crude vibration sensor is your finger nails, very lightly touch your finger nails to a surface, often you can feel vibrations that are difficult to feel with the pads of your fingers, sometimes can be even painfull to do this. Do this at different speeds, if the vibrations/harmonics/cyclelitic frequencies do not change, likely in something that operates at the same speed all the time (motor, any primary drive pulleys). If there is change, likely in the driven components.
Check the drive belt for any rough spots, look closely at any seams, some belts have an obvious joint seam, check the width of the belt and the height/depth of the belt, should be consistent. Have seen a belt with a bad area at a seam/joint, made a slight “crick in the belt”. It was new.
Bearings can be the cause of cycling noises, the wrong lube, too much lube, lack of lube. Sometimes lube is moved around in the bearing, rotating also at a different speed then a race which has caused vibration issues. Normal, often, no, but has.
Lastly, is the cause a turning component or something lose vibrating causing a noise/cycling harmonic maybe not even on the machine. Have seen a wall panel vibrating slightly in and out of sink? with a machine. When I was in collage, was told of a large engine that had a bad vibration, engine was nearly custom rebuilt, and fully balanced, crank, pistons, rods, anything moving was checked. Turned out to be flywheel, nearly a pound out of balance, manufacturer said there was no way, and how would they have checked one that large anyway as there was no balancing equipment that large in western Canada at that time. Answer was “ever hear of a wheel balancer”.
All of the above maybe known and have been checked, but hey, remember @Susquatch ‘s saying.
Check the drive belt for any rough spots, look closely at any seams, some belts have an obvious joint seam, check the width of the belt and the height/depth of the belt, should be consistent. Have seen a belt with a bad area at a seam/joint, made a slight “crick in the belt”. It was new.
Bearings can be the cause of cycling noises, the wrong lube, too much lube, lack of lube. Sometimes lube is moved around in the bearing, rotating also at a different speed then a race which has caused vibration issues. Normal, often, no, but has.
Lastly, is the cause a turning component or something lose vibrating causing a noise/cycling harmonic maybe not even on the machine. Have seen a wall panel vibrating slightly in and out of sink? with a machine. When I was in collage, was told of a large engine that had a bad vibration, engine was nearly custom rebuilt, and fully balanced, crank, pistons, rods, anything moving was checked. Turned out to be flywheel, nearly a pound out of balance, manufacturer said there was no way, and how would they have checked one that large anyway as there was no balancing equipment that large in western Canada at that time. Answer was “ever hear of a wheel balancer”.
All of the above maybe known and have been checked, but hey, remember @Susquatch ‘s saying.
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I don't know how this fits in to the conversation. Years ago I was living on a rural road in Northern Ontario. Hydro was seriously limiting my Amateur Radio Hobby. Radio frequency noise and 115 voltage instability. For the RF interference I walked up and down the road with a handheld Transistor radio and traced the noise to one pole in particular .Numerous calls to Ontario Hydro didn't get it resolved until I was referred to one of their engineers. Two problems were found. Old leaky pole insulators were the cause of the RF interference and an improperly bonded neutral at the pole transformer caused the voltage fluctuations. In essence inside my house the supposedly zero volt neutral was not zero. In the end hydro reran the cable from the pole to my house and installed a new ground at the meter. They also replaced a number of insulators on the poles along the road.
I think that there is a lot of over thinking going on here.
First, is the problem a vibration in the machine? Or an unstable spindle speed?
If the question is 'can bad power from the mains cause that', then the answer is yes to both. But there are limited number of ways. If you want to prove that this is not happening, than an oscilloscope can do that. Unless your power is very bad, this is unlikely because AC induction motors generally develop a 'symbiosis' with their input when at idle (some constant load) as the erratic wave forms are probably drowned out by the momentum of the rotating mass
If the question is 'is there something wrong with my motor that causes that', then you would look at the electrical / mechanical parts of the motor (shorts, capacitors, coil resistance, bearings, rotator balance etc.). Lots of things to check, but most of them would go just as wrong with the motor not mounted.
if the question is 'is there something _about_ my motor that causes that', then you would look at harmonics within the drive train or machine frame. This only really makes sense if it is a vibration, and it is a much more complex topic.
First, is the problem a vibration in the machine? Or an unstable spindle speed?
If the question is 'can bad power from the mains cause that', then the answer is yes to both. But there are limited number of ways. If you want to prove that this is not happening, than an oscilloscope can do that. Unless your power is very bad, this is unlikely because AC induction motors generally develop a 'symbiosis' with their input when at idle (some constant load) as the erratic wave forms are probably drowned out by the momentum of the rotating mass
If the question is 'is there something wrong with my motor that causes that', then you would look at the electrical / mechanical parts of the motor (shorts, capacitors, coil resistance, bearings, rotator balance etc.). Lots of things to check, but most of them would go just as wrong with the motor not mounted.
if the question is 'is there something _about_ my motor that causes that', then you would look at harmonics within the drive train or machine frame. This only really makes sense if it is a vibration, and it is a much more complex topic.
When the motor was removed, it was put on the floor beside the mill & visually examined. It turned very smoothly, no bearing noise, no scratchiness. No axial play. No rotational play like in a key seat holding the sheave steady. The sheave plus (now compressed) bottom spring assembly is still intact, everything is solid & tight in that regard. Motor was held hand (for safety) & turned on/off in FWD & REV many times. It spun up very nicely, no adverse noises, very smooth actually. No visible wobble in sheave. We didn't put a speedometer on it, I thought about that much later that I actually had a hand held laser dot device I could have used. We did not put DTI on the wheel to quantify any runout either. I regret not taking that step because it would not have taken much time, but I think I can replicate both in the machine, just less convenient & of course no longer isolated. The thinking at that point was - nothing obvious with motor, so probably in the head.
You can make out the timing mark & balancing holes, so some hopefully positive indication the parts are of decent quality. Of course, cant see the windings or know much more in that regard. If I didn't mention already, this is with a millwright / service tech present who has seen these before (and the meter is running). So not rushing but more or less following some logic that motor passed the sniff test so lets move onto the head & drive train.
I have no basis to suspect my wall power is suspect, so didn't want to assume anything. But by the same token when it comes to electrical, I don't know what I don't know, so conversation is beneficial. My gut feel is its 'mechanical' but obviously if I knew exactly where it was coming from, it would be fixed & nothing to talk about LOL.
You can make out the timing mark & balancing holes, so some hopefully positive indication the parts are of decent quality. Of course, cant see the windings or know much more in that regard. If I didn't mention already, this is with a millwright / service tech present who has seen these before (and the meter is running). So not rushing but more or less following some logic that motor passed the sniff test so lets move onto the head & drive train.
I have no basis to suspect my wall power is suspect, so didn't want to assume anything. But by the same token when it comes to electrical, I don't know what I don't know, so conversation is beneficial. My gut feel is its 'mechanical' but obviously if I knew exactly where it was coming from, it would be fixed & nothing to talk about LOL.
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Can you make a recording of the noise that you hear? Even from a cell phone? If it lets you, save in an uncompressed format (.wav)
If you know the gear / pully ratio(s) in the machine, that could help you to isolate what rotating parts represent possible sources
If you know the gear / pully ratio(s) in the machine, that could help you to isolate what rotating parts represent possible sources