Lathe motor vibrates entire machine

[galland]

I bought my Grizzly lathe  (model G1550) 25 years ago. Was just down cleaning it and got thinking back to when I first got it. Was very excited till I turned it on for the first time. I had ordered the optional metal stand and I think the neighbors practically heard it. Remember the old cartoons where someone bends and releases the long hand saw and it vibrates and rings big time. The lathe had the stand wailing to beat the band. This was on slow speed. I took the belt off so only the motor was running and no change. I assumed I got a bad motor and pulled it off the lathe. I sat it on the cement floor and wired it back up. I put one foot on top of it so it would not race around the garage at 50 mph. I held my breath and plugged it in. I had to look down to see if it was running. Smooth as silk with a gentle hum. I was shocked. I went and got a nice piece of 3/4 inch flat plate that I knew was perfectly flat and set it on my bench and gently set the motor mounting pad on it. Nice fit with no twist or bind. Went over and cleaned the mounting pad on the lathe and put the plate on the pad. Again a perfect fit and the plate seemed to line up with the headstock. Put motor back on lathe and checked alignment in all directions. Turned on lathe and it shook the same as before. Called Grizzly, pulled motor and sent it to them. In the mean time built a nice wooden stand that was 50% deeper front to rear than the metal one. Motor came back and no change. Even tried with lathe not bolted down just in case I was putting a twist in it. Before I finish this does anyone have any good ideas because even today it is not right. Got it good enough to use but not right.

     Gary

[zeeprogrammer]

I can't help any but I'm interested in seeing what people say.
My new lathe seems to vibrate at a particular speed...not so much below or above that point.

In my mind it usually means something out of balance. Do you have anything mounted to the motor (chuck flange, chuck, etc.)?

Sorry I can't contribute more.

[b.lindsey]

It sure doesn't sound like the motor, so that only leaves the power train (pulleys, v-belts) or something in the
 lathe itself (Chuck, geartrain, etc.).

Bill

[Brian Rupnow]

Most smaller lathes will have a narrow rpm band where small out of balance issues will align with the natural harmonics of the machine itself, and will vibrate. A heavier more solid base helps. Things to check --type of belt gets a big nod, as some belts will make a machine vibrate. Is the vibration the same with chuck on--with chuck off---with faceplate on. Is there a possibility that the spindle may have been bent by improper slinging of the lathe to load or unload it. Do the main spindle bearings have the correct preload on them.---Brian

[Mike R]

When you say the lathe shook with just the motor running - was the pulley still installed?  And when you removed the motor from the machine did you remove the pulley?  You can see where I'm going here - the pulley is the #1 suspect at the moment.  Especially if its a cast iron one.  Try running with and without the pulley to see if its the cause.  Could be out of balance, drilled off center, etc.
Mike

[galland]

Thanks for the info guys. The fact that I dealt with this 25 years ago I honestly can't remember everything I tried to correct the problem. This lathe is a earlier version of their G4000 that they sell now. Mine was made in Taiwan and the G4000 is from China. It has the 9 sp. quick change gear system. Here is how I have been running it for the last 23-24 years. Put a large chunk of 2x8 on top of the stand and under the motor. Find various thicknesses of rubber to wedge between 2x8 and bottom of motor. Completely remove bottom two bolts holding motor to lathe. Lightly tighten top two bolts using rubber washers between motor and lathe mounting pad. Now I did try using all 4 mounting bolts that way but as each bolt is slowly tightened with the motor running the vibration increases. With the motor resting on its rubber pad with only the top two lightly tightened the lathe runs fine other than a minor pattern put into the finish of the metal I have turned. If you start to tighten up the motor more the minor pattern goes major. I have got so used to it that it doesn't really bother me anymore but was just curious what some of you would think. Oh and Brian this lathe uses those expensive small V belts. I think their about 3/16 wide. Mike the vibration did not change whether the pulley was on or off.

[john mills]

look at the stand does it sit flat on the floor does the lath sit flat on the stand does the stand sound drummy without the lathe on it  i  find some of these stands far too light and will send noisy what ever you put on it .If the motor was the problem  it would have been noisey off the machine on the floor.   I do have a habit of making things heavy but in this case  could not be too heavy.

[b.lindsey]

Another question galland....what happens when the motor is mounted to the stand but the v-belts are not connected to the lathe...meaning the motor alone is just hanging on the stand and running by itself?

Bill

[Tennessee Whiskey]

Have you tried it without the chuck installed?

Cletus

[Admiral_dk]

In my line of (repair) work - you divide and conquer    => is the error in the first or the last half, divide the half with the error, etc.

So in line with all the good suggestions - disconnect the power train in halves - and since you only have a few parts still connected to the motor, with the problem still there - just continue dividing 

Best wishes

Per

[crueby]

In my line of (repair) work - you divide and conquer    => is the error in the first or the last half, divide the half with the error, etc.

So in line with all the good suggestions - disconnect the power train in halves - and since you only have a few parts still connected to the motor, with the problem still there - just continue dividing 

Best wishes

Per

In my past life as a software guy we called that 'building fences' to isolate a bug.

As was mentioned earlier, it may just be the slight vibration from motor, belt, whatever, finding the resonant frequency of the stand or bed and exagerating it many times. Sometimes clamping a heavy bar to a cross member on the stand or bed will change that frequency and make the problem go away. Or, just change which RPM it happens at. It can be maddening to find sometimes, especially when its some part of your car doing it at certain speeds, and its someplace you cant reach while driving!   

[galland]

Thanks guys for all the replies and possible ideas. After reading everything from all of you I think I will just pull the motor off and put it back on as it came from the factory and just start all over again. Originally it did vibrate and make a racket with the drive belt removed which I always assumed couldn't be anything in the lathe drivetrain since nothing was moving. Maybe after about 25 years of use it will be like me (tired and not wanting to fight any more). Thanks again for all the input.
     
       Gary

[Stuart]

In my line of (repair) work - you divide and conquer    => is the error in the first or the last half, divide the half with the error, etc.

So in line with all the good suggestions - disconnect the power train in halves - and since you only have a few parts still connected to the motor, with the problem still there - just continue dividing 

Best wishes

Per

Per
That’s the method I have used all my w***king life as a sparks it worked a treat my mentor showed me during my time and I have used it since

Stuart

[ShopShoe]

What everybody already said.

Isolating things one at a time may find it in time. I would still suspect the pulleys. I also think that even with isolation you have tried you might be tweaking the motor mount when mounting the motor.

I have found a mechanic's stethoscope a good tool to help locate a point source for a noise. Some of them come with a vibration probe/diaphragm attachment for this purpose. (Not too many bucks from your local auto parts store.) Sometimes a short piece of hose will work as well.

I also sometimes "go back to square one" and get out my levels and make sure things are level "just because....."

And from an old-timer I knew: Develop the skill of touching things very lightly: "If you grip it or push it your own muscles will keep you from feeling the play or the vibration." It took me awhile, but now I know what he was getting at.

ShopShoe

[john mills]

time to look more at the stand if you could take the machine of the stand and sit it an the concrete floor it would be quiet

[zeeprogrammer]

Thank you Gary for bring this up. And thanks to all the responders. I've been having similar issues and this thread is very helpful. 

[10KPete]

I've had a 'noise' in my 10K since I rebuilt it around 10 years ago. It's something in the lower drive unit that seems to be contacting the sheet metal somewhere under there. At least I'm sure that's what it is. It's nothing serious or out of balance but it sure is annoying.

This thread is pushing me to get under there and find/fix it.

I hope it's easy.....

Pete

[gerritv]

My approach would be more direct;

Mount motor, if no shaking
      Mount pulley to motor, if no shaking
           Mount belt to next pulley/idler, if no shaking
etc.
It could e.g. be a pulley with out-of-centre hole thus acting as an out of balance flywheel. Or a really badly made v-belt, with lumps.

You have already eliminated the motor itself from your previous investigations.

Given the simplicity of the drive train it doesn't seem worthwhile doing the 'binary search' approach that otherwise works so well.

gerrit

[Mcgyver]

I'm having a hard time following the story here.

25 years ago the motor ran smoothly off the lathe but created a huge amount of noise on the lathe, even without the belt disconnected.  Correct? 

That seems clearly a resonance and natural frequency problem....very small bit of vibration at the motor happens to be at the stands natural frequency, and like solders not breaking step on a bridge, the energy builds up and the magnitude of the wave increases.  To change a natural frequency, you have to change the stiffness of the stand (natural frequency is function of weight and stiffness) But how did we get to today and what is today's problem? 

you specifically say you took the belt off and it still did it - why are we considering chucks and belts if that's the case?

confused. 

[Stuart]

Your not the only one

Ok first is this a single phase motor ? Or three phase

Has the belt pulley been removed for testing ?

My first step would be motor mounted on lathe correctly , without the pulley , what happens , if you still get vibration it’s the motor ,if ok then put the pulley one and test

You have to start with only one variable at a time test and add each single component

If the motor is three phase how are you supplying it with power proper three phase from the power company or are you simulating it from single phase

If it’s single phase then these are not the smoothest device and it could just set up a resonance as mentioned by others
 One last point is the motor being powered with the same frequency as the name plate

Stuart