How much motor vibration is too much?

[Ty Williams]

Since I finally have space to set it up, I've taken my grandfather's table saw out of storage and I'm working on bringing it back into fighting trim. I noticed excessive vibration and the pulley was blurry the first time I turned the motor on. I removed the pulley and the key stock. With the pulley removed, the motor vibrated less but still shook more than I've ever felt an electric motor do before. The only other electric motors I have (that aren't integrated into the body of a tool) all run nearly perfectly still with just a faint feeling of rushing if you put your hand on it. This one shakes and sort of reminds me of a weed whacker engine.

Does this mean the motor is faulty? If so, is this likely to be something that can be repaired or is it time to look for a new motor?

[Kyle VanMeter]

Any excessive vibration from the motor will cause premature wear on your arbor, motor bearings, and mount. I would definitely try to narrow down where the vibration is coming from. If you don't you are asking for trouble in the long run. Keep in mind that the vibration may be coming from multiple places.

First off, what kind of saw is it and how old? If it was your grandfathers machine, and it has some age, you may need to replace the motor bearings. Bad bearings can cause many undesirable effects, and may possibly be the source of your vibration.

You also will want to check the saw arbor and motor shaft for excessive runout. If you find that there is a lot more than a few thousandths of runout, that could definitely cause vibration. If all checks out with the motor, replace the belt and keep working your way up the drive system to try and pinpoint the cause of your vibration.

Let us know what you come up with.


Kyle VanMeter

[Ty Williams]

The saw is a Craftsman Model "100", part number 113.29992. The motor is a Craftsman 113.12170. My grandmother thinks this is the first saw my grandfather bought a couple of years after he got back from the war in Europe when he built their house. If she's right, that'd put it somewhere in the early 1950s. That agrees with looking at online pictures of early 1950s Craftsman saws that have the same styling on the rip fence and the saw base.

The motor is currently not attached to the saw. I'm going over everything piece by piece. So the vibration I'm talking about is present with the motor just clamped to the workbench. I have the original instruction sheets for both the saw and the motor and neither list a repair part number for the bearing. That might mean the bearings are non-serviceable.

[Erik Manchester]

Ty,

The motor has likely got 30+ years of crud in the bearings that may have corroded while in storage. You are likely only looking at 1 HP motor which should be easy to replace with a used one. The other option is to take the motor down and replace the bearings.

[Julie Moriarty]

The motor should not vibrate noticeably when separated from everything else. You could take it apart and check for wear, missing fan blades or anything broken off the rotor assembly. The fact it vibrates so much makes me think something broke off and upset the balance. Here's an exploded view of a typical motor
http://www.jameselectric.ca/wp-content/uploads/2013/04/Single_Phase_Motor_Exploded.jpg
Some motors can be difficult to disassemble. You just have to work with it until it comes apart. Once apart, you should see why it's vibrating so badly.

[Erik Manchester]

With old motors long in storage the grease in the bearings may have settled and hardened on one side of the arbor which would create a significant imbalance and resulting vibration. If I were going to go through the effort to clean the bearings I would just replace them as they are not expensive.

[Ty Williams]

Well, another issue. Like I said in the first post, I noticed the pulley wobbled badly. The bore of the pulley was a mess, so I bought a new pulley. It wobbles just as badly. The shaft only has 0.001" runout at the tip but the side of the pulley is moving more like .100-.130". Is there anything that can be done short of junking the pulley?

[Ronald Blue]

What is the motor shaft size? The pulley has to be very sloppy to have that much run out. That is about 1/8". Pulleys are often aluminum on such saws but if it is steel then the shaft may have taken the brunt of the wear. I would expect a 1 hp motor to have a 5/8" (.625) diameter shaft. Regardless though if it is more the .001-.002 below a nominal dimension it will be a source of trouble. Of course any slop on the shaft is multiplied at the outer diameter of the pulley. If the shaft has more wear then this you are probably better served tracking down a replacement motor. Bearings would not be to expensive or difficult to find and as previously mentioned sitting for a long period is hard on them.

[Ty Williams]

OK, I got back out there with the intent to do nothing but measure things to try to figure this out.

I confirmed that the runout in the motor shaft is only 0.001".

I mic'd the shaft and it measures 0.6243" to 0.06247". In other words, it's running 3 to 7 ten thousandths of an inch under the 0.625" it should be for a 5/8" shaft. That's good enough, I would think. It doesn't appear to have worn ovoid either but the presence of the keyway makes that a bit hard to check. The 1/4" of shaft right at the tip is tapered considerably.

Both the old pulley and the brand new one are TERRIBLE. The old pulley feels like it might have less than a thousandth of clearance but also feels like it might be just sticking on a high spot. It has 0.024" wobble (measured at the middle of the face where the belt would ride at a 45* angle to the shaft) and 0.013" of runout measured perpendicular to the shaft. The new pulley has 0.014" runout perpendicular to the shaft and 0.013" of wobble (measured the same way) and has at least 7-8 thousandths clearance to the shaft based on how easy it is to move. With the set screw loose, I can rock the pulley back and forth enough to produce 0.030" movement at the edge of the pulley. Pushing the pulley in the same direction the set screw does improved the wobble but it won't go far enough in that direction to true up.

So did I just win the annoying lottery and get 2 crap pulleys in a row or is there possibly something more problematic going on here?

[Dan Hintz]

The shaft only has 0.001" runout at the tip but the side of the pulley is moving more like .100-.130". Is there anything that can be done short of junking the pulley?

How are you measuring all of this? The shaft may only wobble 1 mil, but when you place the pulley on it, the edge of the pulley is going to amplify that movement. If a 10" radius pulley shows a 10 mil wobble, a 20" pulley will show a 20 mil wobble, etc. Get rid of the shaft eccentricity and everything will likely settle down from there.

[Jerome Stanek]

How are you measuring all of this? The shaft may only wobble 1 mil, but when you place the pulley on it, the edge of the pulley is going to amplify that movement. If a 10" radius pulley shows a 10 mil wobble, a 20" pulley will show a 20 mil wobble, etc. Get rid of the shaft eccentricity and everything will likely settle down from there.


Wouldn't a 10 inch pulley be out 5mm not 10mm only half the diameter.

[Richard Coers]

How much did you pay for the pulley and where did you buy it from? Those cheap die cast pulleys you get at the hardware store aren't worth the pot metal the chinese put in them. Go to McMaster Carr or Graingers and get a real pulley. But if that motor vibrates on the bench, a $100 pulley won't make that smooth. Take it to a motor shop.

[Ty Williams]

How are you measuring all of this? The shaft may only wobble 1 mil, but when you place the pulley on it, the edge of the pulley is going to amplify that movement. If a 10" radius pulley shows a 10 mil wobble, a 20" pulley will show a 20 mil wobble, etc. Get rid of the shaft eccentricity and everything will likely settle down from there.
I've got standard metrology tools. The pulley is only 2.5". That's not enough radius to magnify the 1 thou of runout into the large wobble, not to mention the pulley is loose on the shaft.

Paid about $11 for the pulley at the hardware store.

[Richard Coers]

Is the pulley machined? You can get packages for tuning up table saws, with precision machined steel pulleys and link belts. Here is just an example, no idea if they are the cheapest or not. http://www.in-lineindustries.com/performance_pack.html

[Dan Hintz]

The pulley is only 2.5". That's not enough radius to magnify the 1 thou of runout into the large wobble, not to mention the pulley is loose on the shaft.

Fair enough, but the principle still holds... if there is wobble in the shaft, it will be magnified by the pulley. You have to get that shaft running true first, before you try to get anything else running true.

[Dan Hintz]

Wouldn't a 10 inch pulley be out 5mm not 10mm only half the diameter.
Looking at your line of reasoning, note that I did say radius, not diameter.

Even so, the 10 and 20mm measurements were only examples and have no immediate relation to how much wobble would be in the pulley. If the shaft was angled, then yes, the relationship will be linear... if the shaft was simply running non-concentric to its centerline, then the amount of pulley wobble might be zero.

[Ty Williams]

I bought 3 more pulleys today. All of them are not concentric to their own bores. I can't believe this stuff actually gets sold.

[Duane Meadows]

Buying a bunch of junk pulleys in hopes of finding a good one is not likely to get you anywhere. I'd change the motor bearings first and see if it that stops the vibration. If not, then a different motor is in order. The fact the the run out is .001" while not running really doesn't tell you whether the bearings are good/bad! After the motor issue is resolved, buy a quality pulley and that should solve the motor/pulley issues. It should cost less than the 4 junk pulleys you bought.

Before even going to all that expense, it is probably worth checking the arbor runout and and the condition of the rest of the saw before spending money. Also consider changing the arbor bearings as a precaution anyway. Unless you are determined to make this saw work regardless of cost, you may well save yourself some time and money!

[Mike Delyster]

Buying a bunch of junk pulleys in hopes of finding a good one is not likely to get you anywhere. I'd change the motor bearings first and see it that stops the vibration. If not, then a different motor is order. The fact the the run out is .001" while not running really doesn't tell you whether the bearings are good/bad! After the motor issue is resolved, buy a quality pulley and that should solve the motor/pulley issues. It should cost less than the 4 junk pulleys you bought.

Before even going to all that expense, it is probably worth checking the arbor runout and and the condition of the rest of the saw before spending money. Also consider changing the arbor bearings as a precaution anyway. Unless you are determined to make this saw work regardless of cost, you may well save yourself some time and money!

I agree with Duane and the others here.

Start with the motor bearings first, there easy to replace and don't cost much. Bad motor bearing can cause more vibration then one might think.
Arbor runout and the condition of the rest of the saw is the most important thing to consider, arbor bearing should also be easy to replace.

[Tom Henderson2]

Take the motor to a local motor shop and have them check it out if you don't have experience replacing bearings. It won't be too expensive.

buy a set of machined pulleys from inline or other source.

If you are serious about rehabbing the saw, pull the arbor and have it tried up at a machine shop and the bearings replaced. The motor shop can probably do that too.

i have a similar saw, mid-sixties vintage, and after reworking the arbor and motor and buying a quality blade it is smooth as glass and cts 2" thick hardwood easily.

one thing to check before going further is the top flatness and wear in the miter gage grooves. If the saw was heavily used it may have issues in the top/grooves that are not easily fixable.

my $0.02!