Oscillation/Vibration in lathe

[calgaryguy]

Couple of updates:

Removed 3 jaw chuck. Oscillation at 900rpm belt/gearbox setting is unchanged from what I observed and posted in the video. Tested all 7 other speeds available, some show next to no oscillation on the dial indicator, some show .001-.002. 900 RPM is the worst with about .005 oscillation as shown in the video. Oscillation at 1500rpm setting (top speed for this lathe) is almost nonexistant.

A side note on speeds on this lathe. The original 3 phase 1/3hp motor plate said something to the effect of 1650 rpm. Its since been replaced with a 1725rpm single phase motor. I havent measured spindle rpm yet with any sort of device but I suspect the actual gearbox/pulley speeds will be slightly higher than the original ones noted on the gearbox nameplate.

 

[phaxtris]

You could have a gear in the spindle gear box that is slightly out of balance and happens to hit it's stride at the 900 rpm setting, might not even exist with the original slower motor

 

[jcdammeyer]

Was the pulley used on the 3 phase motor transferred to the new single phase motor? Or is it a different pulley?
The reason I ask this is I've found that the zinc pulleys I used on my Gingery Lathe were notoriously not really round nor were the shaft holes precise. So it has vibration.

And having cast and machined my own pulleys (poorly I might add on bore size) the driving pulley on the mill is almost imperceptibly slightly loose on the motor shaft. And it's enough that I also get vibration at the higher RPMs. I've not fixed that yet because the plan is to change over to toothed belts.

When I do it again, I'll make sure that the arbor used is identical in diameter to the motor shaft and the arbor will be a lot shorter. The pulley was turned between centers so it could be taken out and reversed in order to be able to properly turn the pulley flanks without major reset of the compound slide and to make turning the hub easier.

 

[calgaryguy]

Same pulley as was on the old 3 phase motor. Both were 5/8" shaft/bore size.

 

[jcdammeyer]

Same pulley as was on the old 3 phase motor. Both were 5/8" shaft/bore size.

So somewhere in the chain something is no longer (or maybe never was) balanced or out of round. Good that you've eliminated the chuck.

 

[garageguy]

Have you checked for a loose bearing somewhere in the drive line? They can run smooth at certain rpm's and then start to vibrate as speed increases. (or decreases) Most common with bushing types.

 

[YYCHM]

9" SM Utilathe Restoration

Would I lie to you??????? never,,,,,, I might BS you a bunch but never lie to you,LOL. So if you have the same jiggle with the spindle in neutral or engaged then I think I would take out the pulley shaft and check the bearings. Even if the bearings seem okay I would still remove the gear...

canadianhobbymetalworkers.com

 

[Susquatch]

If I may, I agree with what @jcdammeyer said earlier in v this thread. You have waaaay too many variables going on at once. The other thing is that your video really doesn't let me see what is happening there.

My advice is to get someone who lives around there to drop by and look at it. From my perspective it could be anything from bench feet to loose parts to harmonics to gears to balance to to to to.

If you can't get somebody to drop by, disconnect everything and start with just a spinning motor - with no belt. Then add stuff one at a time.

Your indicator could be harmonic indicator shake in the indicator itself. Unless you are sure it isn't lying, use your hands instead. If you really want to know what happening, use your teeth (just kidding but you get the idea).

Best indicator for stuff that shakes is an old guy who grew up around machines like that.

My two cents from half way around the world.

 

[CWelkie]

use your teeth (just kidding but you get the idea)

Reminds me of a story from the development of the Rolls Royce Merlin engine ... apparently test engineers would check for detonation in an engine running in a test cell with a piece of metal between their teeth.

Seems engineers were made of sterner stuff back then.

 

[Susquatch]

Reminds me of a story from the development of the Rolls Royce Merlin engine ... apparently test engineers would check for detonation in an engine running in a test cell with a piece of metal between their teeth.

Seems engineers were made of sterner stuff back then.

Don't know about sterner stuff.....

I was part of an engine design team for a portion of my career. Detonation creates an abnormal vibration in an engine because there are two flame fronts and peak pressure occurs too early in the process - typically before top dead center. Sometimes it is called knock if it causes the piston connecting rod to touch the bearings. More often it is a pinging noise caused by the two flame fronts.

Either way, I can see how a sheet of metal might send signals to a stern engineers head!

Today, we have inexpensive systems in the lab that can monitor the entire process in great detail. And of course most vehicles have knock sensors now so no engineers get injured or hurt in testing.

My joke actually has a serious side though. The teeth and tongue are very sensitive and things like knock and other vibrations are easily detected where other methods fail. For example the human tongue can detect a height difference of just one micron!

If one was so inclined...... One actually could get a bite on the tailstock and get an incredibly good sense of how much vibration was going on!

Anyone who tries it should probably not admit it......

 

[historicalarms]

Reminds me of a story from the development of the Rolls Royce Merlin engine ... apparently test engineers would check for detonation in an engine running in a test cell with a piece of metal between their teeth.

Seems engineers were made of sterner stuff back then.

I got a lesson on sound transfer years ago by an old man and a D9 cat engine. I fire a D9 engine one morning to warm up for the crew and shortly after starting that ol' girl started hammering like a trip hammer. The old ( old enough that he shouldnt even have been on the jobsite) owner of the machine was close by and came over to investigate where 40 or 50 thousand of his dollars were going in the next few days. after listening for a minute we kind of came to a hopefull conclusion that it was just an injector knocking, not a rod....but now the question is "which hole" is hammering.
That old dude walked to my pick-up and grabbed a length of surveying lath from the box...ya, one of those 4 ft long rough cut pieces of wood sharpened on one end. The old guy touched the sharp end of that wood to the engine block and the flat end tight against his "good ear"....I thought "well that old guy has finally flipped out big time and time to call his family" ...but damned if he didnt go down from cylinder to cylinder and turned to me and the mechanic who had showed up "its # 4". He handed me the stick to confirm but i sure didnt want to be the next on accused of being a lunatic so relented to the mechanic to giv'er a try . The look on his face when he got to #4 told me it was safe to take my turn....that 30 cent piece of wood was better than any stethoscope I ever used.

 

[PeterT]

I had a harmonic vibration on my 14x40 lathe that was related to the motor mount. Its kind of a swing plate affair. The idea is you can accommodate slightly different belt lengths or adjust for belt elongation to some extent. But once you get tension set, you are supposed to secure plate/motor in position so its locked. At some point I either ran out of adjustment room or got forgetful. With the plate a bit loose it would start to do a harmonic bounce at certain rpms, which was also evident in the cutting finish.

Did you think it was vibration free before & now something changed? Or do you feel you are picking something up that was there all along & you are just noticing it now more with run time familiarity?

 

[YYCHM]

Same pulley as was on the old 3 phase motor. Both were 5/8" shaft/bore size.

Have you reached any conclusions regarding the vibration issue yet?

 

[calgaryguy]

Have reached any conclusions regarding the vibration issue yet?

Its either in the headstock (I dont think so instinctively), QC gearbox or lead screw (maybe?) or its in one or both of the drive step pulleys (most likely IMO). The baldor motor I put on this was brand new in the box and super smooth when bench run.

Unless someone chimes in and says 'thats bad and it will affect the precision of your cuts' I'm inclined to ignore it now. This thread has had a fair number of views and if this was a common 'bad' thing I'm sure I would have heard by now.

 

[calgaryguy]

Did you think it was vibration free before & now something changed? Or do you feel you are picking something up that was there all along & you are just noticing it now more with run time familiarity?

Its never been vibration/oscillation free. I've heard/felt the subtle oscillation in the past at the noted specific rpms, but had no idea how I'd communicate it in this forum to pose the question "is this bad/wrong?". The dial indicator oscillation in the video link above visually shows what I've been hearing and feeling in the machine.

 

[YYCHM]

Its either in the headstock (I dont think so instinctively), QC gearbox or lead screw (maybe?) or its in one or both of the drive step pulleys (most likely IMO). The baldor motor I put on this was brand new in the box and super smooth when bench run.

Unless someone chimes in and says 'thats bad and it will affect the precision of your cuts' I'm inclined to ignore it now. This thread has had a fair number of views and if this was a common 'bad' thing I'm sure I would have heard by now.

Did you try lifting the motor and slacken the belt tension as I discovered?

 

[calgaryguy]

Did you try lifting the motor and slacken the belt tension as I discovered?

Yes I did. It didnt seem to have any effect on the oscillation.

 

[jcdammeyer]

Yes I did. It didnt seem to have any effect on the oscillation.

You had a dial indicator on the tail stock. Can you put it on the driving pulley and then on the driven pulley? Obviously not powered.
Is it possible to remove a gear or something so you are only turning the spindle and not a single gear?

 

[RobinHood]

Generally, any vibration/oscillation affects the performance of machines. So if you can eliminate/reduce them, it would make your lathe perform better. Does the present condition stop you from using it? No. Is it annoying? Yes.

I believe it has been suggested above: try to find out which component (or component combo) causes the issue. I would start with the drive pulleys (you stated the motor itself runs smoothly on the bench).

Disconnect the belt. Run the motor with the drive pulley installed.

Connect the belt. Leave the lathe in neutral and feed disconnected. Run the motor. Repeat for all pulley combos.

Run the lathe in all spindle speeds (feed disconnected), no chuck installed.

Run lathe in all speeds with feed connected (run in all spindle speeds and all feed speeds).
Repeat for reverse feed.

Run the lathe in all speeds (feed disconnected) with 3J and then 4J.

Run lathe with 3J and 4J and feed connected (both forward and reverse) in all spindle speeds and all feed speeds.

I would make a spread sheet or a table. This is going to take a while.

You should be able to find which combo causes the issue.

If you need help, let me know and I can come over at a mutually convenient time.

 

[YYCHM]

@RobinHood has had experience with the 9" Utilathe, so he has some feel for what to expect from one. He had one for a bit.....

SM 9" Utilathe for sale

I have a Standard Modern 9" Utilathe for sale. 22" between centers. QC gear box. Kobayashi (made in Japan) 3 jaw. Pratt (made in England) 4 jaw. Taper attachment. Steady rest. Drive plate. Face plate. QCTP + holders (this was made by the previous owner). Original lantern toolpost with tool...

canadianhobbymetalworkers.com