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lathe vibration problems please can anyone help ?

audio.fi

Aluminum
Joined
Dec 22, 2009
Location
U.K.
Hi,

I have a small (5.5" centre height) Boxford AUD Mk III lathe and have connected it to an IMO I-DRIVE inverter.

The motor is a standard british, Brook Cropmton Parkinson motor. The image attachment link on this web site doesn't seem to be working so here is the motor plate info :-

Model number = V (or could be W)MA544CM1B (spares CAD No 2-V

Wo = 550

R.P.M. 1425

Star V = 380/440

Star A = 1.5

Delta V = 220/240

Delta A = 2.6

Insulation class = E

Phase = 3

Hz = 50

Rating = (looks like it says) CP

It is wired in delta to work from U.K. mains supply i.e. 240V 50Hz

The problem that ever since I got this lathe it is that particularly in the highest belt speed (which gives 1400 r.p.m.) the machine vibrates a lot (much worse on the headstock), and makes a strange low frequency drone that comes in and out in loudness, but is always there; As the speed is reduced, the vibration varies a bit but never is less than objectionable as does the low frequency sound.
I have tried all ways to remove this vibration and sound, and have replaced the pulley bearings (they were worn out anyway) which made only a very slight difference, and changed the belts for different types which did make a difference in that the fenner belts sounded worse than the originals and the toothed v-belts I tried that are more flexible lessened the sound quite a bit, but none removed the vibration.

I did find that removing the equipment door considerably quietened the sound, but this was the right-hand door and the left-hand door (the one in front of the motor), made no difference.

I also found that the headstock was not the cause as I removed the brammer belt but the vibration still existed.

I found that if I slackened the belt off from the first stepped pulley to the counter-shaft, the vibration decreased but then it did not have enough grip to work properly.

Could this be as a result of using an inverter, or could it be a mechanical problem ?

The vibration is such that it is not comfortable to touch the machine (i.e. the cross-slide or top-slide handles), for any length of time.

The machine is bolted to a specially made, level, concrete pedestal.

Any help would be very much appreciated.

Thanks.
 
Try posting in the "
Transformers, Phase Converters and VFD" section. It's about half way down the main page. Someone there may be able to help. Have you looked in the help section in the drive manual? Could be just a programing error.
 
Do a simple test sequence. Remove the belt driving the little lathe. Run the motor. Vibration? It's the motor. No vibration? Add driven parts until it vibrates. Bingo!
 
Is it a resilant mount motor? Partial collapse, usually due to oil soaking at some time, of the rubber bits can give very strange vibration effects.

Check the VFD settings too. Probably best to return them to standard if any have been changed as your motor and application are straight forward. Most VFD units have such a wide range of parameter variation that its quite possible to end up with an unsuitable combination. Personally I've never needed to alter anything more sophisticated than the run-up time.

Verify that all the mountings for motor, plate, and countershaft are properly done up and snugly fitted. A friend once tracked some vibration issues down to a combination of a bolt with either a damaged thread or over length plain shank that wouldn't quite do up and a bit of swarf under the mounting point. The bolt went up just far enough to snug the swarf so it felt tight but was actually barely nipped in place. Swarf soon flattened enough to let things shake. Took ages to find because spanner tests said the bolt was tight.

Clive
 
I hope someone can help as I don't know what to do now !!

I have spent the last week replacing the front bearing on my boxford, and it has gone very well, and last night, I ran the headstock up and all went well, and although it is still vibrating, since loosening the belts, it is reasonable;

However, tonight I had it on for about 30 seconds and it was going fine, then the lathe started to make a loud sort of, buzzing/groaning sound. I switched off and first of all thought I must have done something wrong putting the bearing back (as the sound is similar to metal scraping), but after removing the belt from the motor, it was apparent that the motor was what was making the sound.

Since it was being fed from an inverter, I checked the voltages when the motor was running and they were within a couple of volts of each other on all phases.
Next, I disconnected the inverter, and connected the motor to a run capacitor (I mechanically spun the motor up to speed first), and run it like it was on a phase converter, and it made the same sound.
I removed the motor to inspect it and I can find no physical problems with it and the bearings seem free running, i.e. if spun it takes a while to stop and they make no sound when spun;
I measured the windings with a standard multimeter and across the three terminals they read :- 8.5 ohms, 8.6 ohms, 7.5 ohms; (Is the lower reading significant ?).
Has anyone any idea what is wrong ?
Has the inverter done something to it ?, as I don't want to get another motor and the inverter breaks it again.
Any help appreciated.
Thank you.
 
Take the motor apart. A three phase motor is the simplest thing in the world. You have two end bells with bearings, and a stator trapped between. There is a rotor with no brushes, wires, or anything, just irons and aluminum holding the irons in place. Just be halfway careful not to bang the windings and you'll be fine.

It sure sounds like a bearing problem to me. I'd get the bearings out and spin them by hand. If you feel ANY roughness or they make ANY whizzing noises, they are toast. What might seem insignificant noise will be far worse when the motor is loaded with a belt and pulling the lathe.

If the bearings are good, look to see if something has gotten in the air gap between the stator ID and the rotor. There will be scoring if that is the case. Look for blackened spots or arcing on the stator slots, indicating the insulation has failed. Look for blackened wiring on the ends of the windings, indicating failed and/or overheated insulation. Could be something simple as a washer or large chip that fell into the fan and is getting scoured around inside the cover.

If you have a blown motor (black windings or arcing to the rotor), it could very well be due to the VFD, especially if you have been running at low speeds. VFDs are actually pretty hard on a motor in many different ways, and you really need an inverter duty motor for the job. The company I work at recently had to replace two 100hp motors because they were not inverter duty motors, and were running on VFDs. Made all kinds of racket.
 
Thank you very much for the reply; These instructions are very helpful indeed.

As it happens, when I first got the lathe (and shortly after, the inverter), I had to re-wire the motor for delta (I am in the U.K. so this is required for the inverter to run the motor), I lost a washer from one of the terminals. I could not find it, and as it was horizontal did not pay it much attention (although it did bother me that it was in there), but since then, I totally forgot about it and the motor has been out and on it's end and re-fitted, so it could be that the washer has moved, as I cannot now remember if I found the washer under the motor or not shortly after it was lost.
Anyway, I did shake the motor about tonight after removing it and nothing sounded loose, but I guess it could be trapped. Also, the motor compartment smelt a bit like old electronics (like the inside of an old valve amp), but it has smelt like that before (please understand that this had had virtually no use since I got it, and the half an hour it was in constant use last night was the most it had done and about an hour when I first got it); Perhaps this is the smell of the insulation being burnt. I will follow your instructions tomorrow (It's night time here), and write back when I have had a look at it.

Thanks very much for your help.
 
I have taken the motor apart today. There was a very small piece of metal, between the rotating part and the windings (about 2mm long).

I have checked one of the bearings and after washing the old grease out and spinning it, it would stick every now and then, but after more washing, this seems to have gone, so I re-greased it. I cannot however, get the front bearing out yet, but once I do, I will look at that also.
I looked around at the windings, and there seems nothing burnt, no melted varnish or anything like that, so hopefully, it was just the deris or the bearings.

I'll write back what happens.

Thanks.
 
7.5 Ohm and 8.5 ohm
That is a 12% difference That is much
Check the amps on each leg
And check if the motor gets hot in iddle
You took out a bearing but you didn`t replace it but kept doubting
Why ????
Just for sorting out the possibility Replace those bearings

Peter from Holland
 
Hi,

I was going to replace the bearings if the motor runs o.k. when I put the originals back in. I don't want to buy bearings only to find the windings are burnt out.
I will check the current on each leg to see if they are much different.

Thanks for the advice.
 
Can you better describe the wiring hook up? It sounds like you are using a 3phase motor with an inverter that is hooked to a single phase circuit. Most inverters will do this fine but the HP/KW rating goes way down. You may be getting the vibration from the inverter. I'm curious why it has to run delta vs. wye.

Overly simplified all an inverter does is take the line voltage and store it in big capacitors and then using transistors pick the positive and negative voltages off at the right time and put them to the motor leads to create a three phase sine wave.

Jamie
 
Hi,

I was going to replace the bearings if the motor runs o.k.
Thanks for the advice.


And what if the bearings are the problem ?????
Very hard to determin by just cleaning and spinning by hand
I have replaced bearings wich looked oke for the naked eye and ear but were toasted anyhow

Peter from Holland
 
Got to agree with peterve. Remember what I said about the bearings... if it is not absolutely perfect, it's bad. If that bearing was sticking in any way, shape or form, it's junk. You'll have to replace it to even get an idea of what else is wrong. No big deal, probably just a few bucks at most.

If the piece of metal slung around between the rotor and stator didn't clip any insulation, you may be OK, but that difference in impedence is something worth looking over. Next question, where did the piece of metal come from? Is it part of a bearing shield, that washer you dropped, or a melted piece of rotor iron, stator iron, or copper wire?
 








 
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