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Motor Vibration

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JPMacG

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#1
I am on a mission to identify and eliminate the various sources of vibration on my Craftsman/Atlas lathe. I have replaced some pulleys and the countershaft, and stiffened up the cabinet. One source that I have identified is the motor itself. It vibrates when powered. I ran it without the belt so I know it is the motor, not something else. And I noticed that it only vibrates when powered. When I turn the switch off the vibration stops immediately (while the motor is coasting).

It is a 1/2 HP Atlas branded ball bearing induction motor. I think it is the original motor that came with the lathe, circa 1954. I did some reading and apparently torque pulsations are inherent and unavoidable in single phase induction motors.

I'm wondering about a vibration isolation motor mount. Has anyone gone down this path?
 
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ttabbal

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#2
You could make some rubber spacers to absorb vibration and put them between the motor and whatever it mounts to.

I would get a decent 3 phase motor and VFD though. Very smooth and variable speed.

A newer motor will likely run smoother just due to tighter tolerance and better balancing, even single phase.
 

cathead

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#3
Jon,

After reading this post I am wondering if the bearings could possibly be worn causing an unbalanced condition.
Is there any side play to the bearings? Also could the motor pulley possibly be the problem? It might be worth
your time to take the motor apart and do a bit of inspection.
 

Dave Paine

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#4
I have several single phase motors in my shop and they do not exhibit vibrations. As cathead stated, worth checking the bearings and the pulley. A set screw on the pulley could easily come loose.
 

JR49

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#5
Maybe one of you Electrical gurus out there can give some insight as to why this motor would vibrate while supplied with electricity, but stop vibrating when current is switched off even though it is still spinning fast. Thanks, JR49
 

David S

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#6
Jon did you just get this lathe and notice that the motor vibrates? Or did you own the lathe for some time and the motor used to be fine, but now vibrates. I have a couple of these motors on my machines and none vibrate like you describe.

The fact that it vibrates when powered but doesn't when turned off and coasting down, could possibly indicate bad bearings with excessive play.

David
 

cathead

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#7
Maybe one of you Electrical gurus out there can give some insight as to why this motor would vibrate while supplied with electricity, but stop vibrating when current is switched off even though it is still spinning fast. Thanks, JR49
Magnetism could be pulling the armature away from center causing unbalance. When the unit is turned off the magnetism is gone as well
as the imbalance. I don't know that this is the case but likely possible.
 

JPMacG

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#8
Thanks everyone. I just checked a few things... There is no perceptible axial or radial play in the motor shaft. I ran the motor with the pulley off and the vibration level was about the same as with the pulley mounted. It is not like the motor is shaking. It is that I can feel a vibration with my fingertips when I lightly touch the motor housing. I can also feel the same vibration at a reduced level on the lathe bed.

I have owned the lathe for about 25 years. Just recently I got on a kick of fixing it up... replacing some pulleys that wobbled, etc. I now have it improved to the point that the motor vibration is noticeable. I guess I am being obsessive - most hobbyists would probably consider the motor vibration perfectly acceptable.

I checked the motors on my milling machine, drill press and wood lathe and they have a similar vibration. The drill press ( a small Delta) is actually worse. In each case the vibration stops instantly when I turn off the electric to the motor. I really think it is related to the torque varying as the motor turns through the applied magnetic field.

Going to a 3-phase motor would be the best solution. I was just wondering if anyone had experience with vibration dampening motor mounts. I notice that appliance motors (i.e. HVAC blowers) sometimes have soft mounts.
 

whitmore

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#9
... It vibrates when powered. I ran it without the belt so I know it is the motor, not something else. And I noticed that it only vibrates when powered. When I turn the switch off the vibration stops immediately (while the motor is coasting).
The normal vibration of a single-phase AC motor is the familiar 'refrigerator-hum' at 120 Hz (torque dips twice
per cycle of the 60 Hz AC). It's usually not going to make anything vibrate, though, because the mass of the rotor
acts as a flywheel. If it is a capacitor-run motor, the capacitor can fail, causing excess hum (and eventually
nonstarting). Capacitors are cheap to replace (from generic dealers), but the official repair part might be rare.
You do NOT want a 1954-design identical capacitor. Look up 'PCB capacitor' for too much info.

If the rotor of the motor were to become magnetized, it could cause 60 Hz hum, but that is fairly easy to treat: just run
the motor (maybe with a lightbulb in series, to prevent excess current) into a heavy load, try to nearly stall it. A mechanical
design that damps 120 Hz might not damp 60 Hz vibrations well, and you get 60 Hz torque variations with
an accidentally-magnetized rotor.

If the hum goes away while the motor is coasting, that mainly rules out bearings and bent-shaft and even pulley
imbalance as issues. It doesn't completely rule out mechanical hum, though, because the motor laminations
or windings, if loose, can hum under power, and the fix for that is application of some kind of varnish or impregnation
to fill the cracks.
 

FOMOGO

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#10
You cold static balance them diy, or if you really want smooth have them dynamically balanced. Mike
 

JPMacG

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#11
Interesting thought about the capacitor going bad. The capacitor is likely the original - over 60 years old. I should take it out and check capacity and leakage.
 

cdhknives

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#12
Harmonics can cause strange vibrations at times. Usually experimenting with soft and hard mounts, dampening weights, etc. will help. Sometimes there is no good solution except a new motor. My Atlas requires a precise shim under the 'floating' motor mount or the small irregularities in the pulleys cause occasional motor bouncing. Too much shim and the motor to countershaft belt is loose. Too little and it bounces anyway. It took me almost a year to get it right.
 

cdhknives

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#13
Maybe one of you Electrical gurus out there can give some insight as to why this motor would vibrate while supplied with electricity, but stop vibrating when current is switched off even though it is still spinning fast. Thanks, JR49
It was sort of dealt with above, but to summarize bearings and such act differently under load than when coasting, even when the motor is in a 'no load' condition, internally it is still loaded. Wiring with current running through it moves via magnetic induction. Magnetic fields changing move wires and ferrous metals. Even a simple induction motor has a lot of places that could cause vibrations. For our big industrial motors we see them move quite a bit when powered up vs. resting, so couplings are best installed based on the running shaft position, not the resting position. Smaller scale, but it still happens in little motors.
 

dcsims

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#14
The fact that it runs smooth when coasting pretty much rules out being out of balance dynamically. I would bet on there being a pole in the windings open causing it to surge and coast as it passes the open pole of the motor.

Dennis
 

JPMacG

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#15
Thanks everyone. I will check the capacitor and do the de-mag that Whitmore described. I need to move the lathe away from the wall to get access, so I'll wait until I have a few hours to spend. If these ideas don't work then I'll try a soft motor mount - rubber isolated studs if there is room, or at least a rubber mat under the motor base if not enough room for studs. I'm not to the point of spending the $$ for a 3-phase motor and VFD just yet. I also like preserving the machine in its original form.
 

JPMacG

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#16
I went ahead with the soft motor mounts. These are neoprene rubber mounts from McMaster-Carr. They are 1 inch diameter, 3/4 inch tall and are rated at 50 lbs each. The cost was about $2.50 each. They definitely helped - I can no longer feel the 120 Hz motor torque vibration on the lathe bed with my fingers. I'm not sure how well they will hold up - time will tell. I probably "fixed" something that did not need fixing, but eliminating vibration makes me feel good.

IMG_1998.JPG IMG_1996.JPG
 

markba633csi

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#17
Keep an eye on the rubber- you don't want the motor tearing itself loose- you might consider a couple of safety straps or lanyards from
the motor feet to the mount plate as an extra precaution
Mark
 

Silverbullet

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#18
That type mount usually last many years in normal use . With no oil or other lubes getting to them heat is the only enemy . I've replaced literally hundreds on pressure washers and portable generators, even chainsaws use a mount along the same lines. Oils and gas cause them to break down over time.
 

savarin

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#19
could rubber mounts be used on a drill press if the bolt is also buried in the rubber so there is no steel to steel contact?
 

Dave Paine

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#20
could rubber mounts be used on a drill press if the bolt is also buried in the rubber so there is no steel to steel contact?
I think so, if you just want isolation of vibration rather than bolting to the floor. FYI these may be available with the bolt set in the rubber, or a nut set in the rubber and a separate stud. A picture of the latter I purchased. This was purchased from ENCO, but now available in US at MSC perhaps others sources.

Machine_neoprene_mount_with_stud_8849.jpg
 

savarin

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#21
I mean for the motor, something like this. The vibration in my motor sets up harmonics at different heights of the support pillar.
rubber.jpg
The idea being that the motor mounting plat is totally isolated from the drill head mount.
I'm unsure due to it hanging off in a vertical fashion rather than being horizontal like in a lathe.
 

JPMacG

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#22
I think that the soft mounts that I got from McMaster are intended to be used in compression, not in tension or in shear. I don't know how they would hold up in tension or shear, but I suspect not well.
 

Ray C

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#23
I went ahead with the soft motor mounts. These are neoprene rubber mounts from McMaster-Carr. They are 1 inch diameter, 3/4 inch tall and are rated at 50 lbs each. The cost was about $2.50 each. They definitely helped - I can no longer feel the 120 Hz motor torque vibration on the lathe bed with my fingers. I'm not sure how well they will hold up - time will tell. I probably "fixed" something that did not need fixing, but eliminating vibration makes me feel good.

View attachment 265345 View attachment 265346
I once owned one of these lathes and the topic you mention has been discussed ad-infinitum over the years. Vibration is inherent in that design. All of those extended arms and brackets are prone to transmitting and/or amplifying all sources of vibration. The motor itself sits on a hinged plate and that hinged plate will rise and fall because one side of the pulley is pushing and the other side is pulling. That is the primary source of vibration driven by the mass of the motor. You could lock it down but then, even the slightest unevenness in the belt will be transmitted to all the brackets in that mechanism.

A long time ago, I was knee-deep in an Atlas TH42. I moderated a forum on a website dedicated to those machines. No One ever eliminated all the vibration unless they converted the machine to direct drive.

Ray
 

brino

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#24
Another thought is to try Link-Belt, like this:
http://www.leevalley.com/en/wood/page.aspx?p=30051&cat=1,240,41067

Apparently since each link can move a little with respect to its neighbour, in can help eliminate vibrations being transferred from one pulley to another. I believe it is available in different standard widths from other suppliers.

-brino
 

Silverbullet

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#25
I mean for the motor, something like this. The vibration in my motor sets up harmonics at different heights of the support pillar.
View attachment 265424
The idea being that the motor mounting plat is totally isolated from the drill head mount.
I'm unsure due to it hanging off in a vertical fashion rather than being horizontal like in a lathe.
They would isolate the motor vibrations but not the pulley and belt vibrations. Some but not all.
 

wa5cab

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#26
Nothing directly to do with rubber motor mounts, but I have to add one comment about hinged motor mounts. If doing an interrupted cut, under some circumstances, you can actually get the motor to bouncing rather badly if the only force tensioning the belt is the weight of the motor. Although some of the Atlas motor mounts were hinged for adjustment, once adjusted for the desired belt tension, they were supposed to be locked in place by either a bolt with adjustment and jam nuts (like on my non-Atlas 4X6 band saw ) or by two slotted arms with pinch bolts at each end. Once adjusted and locked, the entire assembly was rigid, at least within the limits of the strength of the parts.
 
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