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Electric motor issue - 1 hp table saw


Mudfly

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Hello,

I have an older craftsmen table saw that I'm having some issues with.  Its a 1 HP 3450 rpm 56Z frame 110/220v motor.  I'm running it on 110.  Anyway, the motor is tired. It will slow down or stall with any load on it at all.   Not sure exactly what to check.  I did put new bearing in the motor a few years ago because the old ones were 'sticky' (I can't remember off hand if it was a combination of a little rust, sawdust, and moisture or what).  It doesn't have many hours since then (maybe like 3 hours of run time).   I haven't pulled it apart again as I wanted to get some ideas of what to watch out for? 

I don't think there is anyone local that rebuilds electric motors otherwise I would bring it in.  I'd like to fix what I have if possible. 

If not does anyone have suggestions for replacement brands?  Grainger has a Dayton for $540 (which seems high).  Then there is a Grizzly that I could order for $280.  That's with minimal google searching.

 

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As always check your connections. This includes plugs, outlets, and the switch. It could be a poor connection causing low voltage to the motor. If you can check voltage with the saw off and then running with a load it would help diagnose the problem. 
If no voltage issues then check to see if it has a run capacitor. They will cause issues if they are bad. You didn’t mention any starting problems but how is it starting?

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45 minutes ago, 12_Guy said:

As always check your connections. This includes plugs, outlets, and the switch. It could be a poor connection causing low voltage to the motor. If you can check voltage with the saw off and then running with a load it would help diagnose the problem. 
If no voltage issues then check to see if it has a run capacitor. They will cause issues if they are bad. You didn’t mention any starting problems but how is it starting?

X2, and check capacitors, both start and run. 

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May not be the issue, but check the pulley on the arbor. I have 4 table saws, one is a Craftsman 3hp. It's a good saw but every couple of years it will have a similar problem. It starts fine, full speed, but when you feed it, the blade will slow, but the motor doesn't pull down. The pulley on the arbor is not keyed, it is simply a set screw on a flat spot on the shaft. Over time, the set screw will vibrate loose and the pulley will spin on the shaft when under load.

 

 

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6 minutes ago, dads706 said:

May not be the issue, but check the pulley on the arbor. I have 4 table saws, one is a Craftsman 3hp. It's a good saw but every couple of years it will have a similar problem. It starts fine, full speed, but when you feed it, the blade will slow, but the motor doesn't pull down. The pulley on the arbor is not keyed, it is simply a set screw on a flat spot on the shaft. Over time, the set screw will vibrate loose and the pulley will spin on the shaft when under load.

 

 

Thanks.  I will check those, but I think the motor is pulling down on mine.  It’s been awhile since I used it, but I thought I stopped the motor last time I did.

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look on flea bay or Amazon! Sometimes you can find odd stuff on there. Some is reasonable some not,--just gotta pick thru the crop! I just got another old Craftsman all cast iron jobber and the motor just trips the breaker when you turn it on,---has the original Craftsman tag on the big old motor. The one I use has a motor with a shaft on both ends and it was a replacement at some point before I got that saw. These saws were built to last, cut great, and are not "tinny" sounding when running.

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1 hour ago, Mudfly said:

So my electrical theory from 20 years ago has failed in my memory.  Best way to test a capacitor?  No continuity is all I remember.

With a capacitor tester of course! LOL 

In all seriousness, many newer digital meters have a cap test function. 
The next best thing is an old analog meter. Set it on a higher resistance scale and put the leads on the cap. After discharging it with a screwdriver first. The needle should start at the left side, swing to the right and return to the left. The speed this happens is dependent upon which setting the meter is on. Hanging out at a particular, usually high, resistance or staying at 0 resistance is bad. 
You can do the same thing with a digital meter but it is a little more difficult to watch the numbers count down and back up. Auto range meters seem to work better when you set it on a particular range first. 
Basically what you need to see is that the cap isn’t shorted - zero resistance nor open -  high resistance. 
You can reverse the test leads to repeat the test over and over until you are satisfied with the results. 

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Capacitors do deteriorate with age. 
I had a three phase generator with four failed electrolytic capacitors. Oddly enough they tested within range on my capacitance tester. As they were old I thought I may as well replace them regardless as they were cheap. Then I could look elsewhere for the fault. Once they were replaced the generator worked fine a gave full output. 

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As said a digital multi meter is misleading. An old style analog is best. Make sure the battery is up to par, you are charging the capacitor with the meter when testing, so you want a good battery to avoid misleading results. If i can find one on the shelf I will try to post a video.

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Tore into the motor tonight.  Nothing obviously wrong to me with the exception of it appears that the thermal over load has been bypassed (first pic).

it was pretty dirty and dusty, but no rust.  Bearings are smooth.

6305019F-A50D-4BCE-A99A-B96CD683B747.thumb.jpeg.d8aef0046496e2f9b36aa8be1c746fcc.jpeg069012A1-0E93-4A55-9C50-8D9A95723F95.thumb.jpeg.7d1c1385017fd438cf5560d2f8efb4fd.jpegC504F8C1-6A93-4749-852B-ED66C8B025B6.thumb.jpeg.8ca4b506331ea68c413c1b7ba8f4b981.jpegC504F8C1-6A93-4749-852B-ED66C8B025B6.thumb.jpeg.8ca4b506331ea68c413c1b7ba8f4b981.jpegF4080D2B-044E-4CD8-B82D-8770D31C112D.thumb.jpeg.5a549c2e1847306211ab12c1feffd978.jpegC867A51C-D505-48C2-8BE9-E3192D8F8E5C.thumb.jpeg.a1d56dbddfda819771b87eee21a1beaa.jpeg

I did put a cheap DMM on the capacitor to check resistance.  It slowly crept up from 0 ohms to outside limit. Took maybe 3-4 seconds.

anyone see anything obviously wrong that I’m missing.

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8 minutes ago, vtfireman85 said:

Looks to me like the contacts on the centrifugal switch are burned, but it is hard to tell in your pics. 

Is this a better pic?  Assuming you meant the copper arm.  Sorry don’t know the correct terms, but that made sense to me at least.

943192CA-DA22-4DAE-8A68-C9505B1E7491.thumb.jpeg.32f21d5d796a920848e275c1dd4ab24d.jpeg

it’s a little gummed up but not ‘burnt’.  At least in my opinion.

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3 minutes ago, vtfireman85 said:

Get the dust off of that and make sure it is making good contact everywhere 

Is it gummed up from dielectric grease and sawdust or just crud? 

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31 minutes ago, vtfireman85 said:

Is it gummed up from dielectric grease and sawdust or just crud? 

Just to confirm, you are talking about the contact that the copper arm touches when it moves towards the camera in the picture I took, correct?  Circled.  If so I don’t know exactly, but could definitely be cleaned.  I’d say sawdust and copper tarnish.0B7CFB62-B680-49D5-872C-ADE9A212F737.thumb.jpeg.f899facce91d9afe9e681d08d709fa6b.jpeg

36 minutes ago, catman13 said:

does it have 2 capacitors, just replace the run and start capacitors they are around 10.00 dollars

Just 1 capacitor.

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I don't have any good answers for you. You don't have a run cap to be bad. I assume that the start switch and start cap are also good based on your test and you have never mentioned any starting issue. The overload is bypassed. I wonder if we are just asking too much from the motor. It would be nice to put an amp meter on it while under load. Not sure if you have one. The dab of grease/dirt on the copper switch arm can just be wiped off. Now as for the contacts, they are going to be difficult to access. They live under the brass cup below the copper arm. They are somewhat enclosed in an effort to prevent dust from causing problems. The little metal arm you have circled is there to limit the switch motion. It keeps the arm from moving closer to the governor and rubbing it when running. To get to the contacts you will have to bend it out of the way so you can flex the copper arm up further. They can break rendering the switch assembly junk as you will need to bend it back to preform its job as mentioned above. Once you have access to the contacts they are still difficult to polish because they are down inside the cups. A normal point file is useless as is emery paper. 

Since it is starting fine, I suggest leaving the switch alone. Perhaps blow it out well with air and electric contact cleaner or brake cleaner. 

It is possible that you have a broken winding somewhere or possibly the motor is not wired correctly. A motor wired for 240v but only receiving 120v may start and run but will not have much power. Double check the wiring. I have seen more than one motor "converted" to run on 120 by changing the cord end. 

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How's the supply voltage? Running on a 15 amp circuit my saw would trip the breaker under load. Since I had 220 nearby I converted it and have zero issues on 220. I could see the lights dim on the 15 amp 110 circuit. Saw would almost stall then breaker would trip.

Since those saws rely on gravity for belt tension check the belt has tension after changing blade height. Mine would sometimes be loose as the motor pivot was sticky. I could hear the motor running in that case.

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