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I wood if I could.
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Discussion Starter · #1 · (Edited)
A few times over the past month my Craftsman bandsaw motor wouldn't start. But a love tap to the motor allowed it to kick on normally. Well it finally stopped starting all together last night, just when I needed to cut some parts, forcing me to have to use one of my lighter-duty bandsaws (which really wasn't up to the task). All it would do is hum when the power was applied.

So I removed the motor and rebuilt it today. I can't be without my band saw. So, since I had to make the repair I figured I put together a real basic tutorial for any one who might be in the same boat and not know what to do about it. Fortunately, I've rebuilt plenty of motors over the years.

Here's the motor I'm dealing with in this case. But this works for MANY motors having capacitor start/centrifugal switches.



Technology Auto part Electronic device Machine Pump


Remove the pulley from the shaft by first loosening the set screw with an allen (hex) wrench. Then remove the bracket that the belt guard attaches to.

Next, remove the clips that secure the motor to the mounting frame. You usually do NOT have to completely remove the bolt/nut, like I did. Just loosen it and you'll be able to spread the clips to detach them.

Technology Auto part Electronic device Pump Automotive starter motor


There are four long bolts with nuts that secure the two end caps of the motor. Remove them and pull off the front end cap. Pull the rotor out as well. Make sure to account for the various washers and seals on the shaft that protect the bushings from dust.

Auto part Differential Rotor Clutch Machine


At this point I went ahead and vacuumed the dust out of the motor and end cap while working the dust free with a brush. Anytime you open a motor you want to be sure to take time to clean it well enough to remove all particles and old grease/oil.

Make sure to clean the vents and the fan blades well. Clean the grime and oil off of the shaft with alcohol or (acetone) on a rag. Clean the various washers and seals as well (with a dry rag, use alcohol if needed).

If tapping the motor ever makes it start when all it would do is hum otherwise, the problem is likely bad contacts on the switch operated by the centrifugal mechanism.

The centrifugal switch is mounted to the rear end cap. I circled the offending contacts in red.

Auto part Clutch Bearing Rotor Automotive engine part
 

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I wood if I could.
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Discussion Starter · #2 · (Edited)
Here's a better look at the workings mounted to the rear end cap. The contacts at fault here are circled in red. Here you can see me restoring the contacts with a burnishing tool (a contact burnishing tool, not the kind of burnishing tool one uses to roll the bur on a scraper). Be sure to put pressure on the top contact with a finger (not shown because I have only two hands and one was holding the camera), while the burnisher is between the two contact points (as shown). This is to make sure you don't bent the contact leaf, causing it to not close fully.

Auto part Engine


The points circled in blue should also be addressed as well. They are quick disconnect connectors. They are often slightly loose and/or tarnished/corroded. Ensure that they are making excellent contact by unplugging them and cleaning the male lugs with very fine sandpaper (300-600 grit).

Auto part Electronics Technology Engine Electronic component


Clean the inside of the female connectors with the same fine sandpaper. In this case, the males were a little less than ideal. But, also, the female ends were a little bit loose. Just enough that they may become a problem in the future by allowing a film of oxidation to build up and increase the resistance of the connection.

After sanding the inside of the female connectors (the contact points) I used my limiting pliers to tighten the connectors without crushing them completely closed.

Auto part Coil


Now that all of the contacts are restored and all of the dust and grime is cleaned out of the motor, use cotton swabs to clean any build-up out of the bushings. There is felt inside the perimeter and core of the bushings. That's there to hold the oil that keeps the shaft and bushings lubricated.

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After cleaning with dry cotton swabs, saturate all of the felt with motor bearing oil, such as 3-In-One motor oil (not automotive motor oil).

Finger Drink
 

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I wood if I could.
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Discussion Starter · #3 · (Edited)
A continuity tester or ohm meter can be used to verify that all contacts are working properly.

Make sure all washers and seals are placed back onto the shafts (in the correct sequence). Before reassembly, make sure to rub a coat of oil onto the shafts at BOTH ends of the rotor. Also make sure you've cleaned the oil and grime off of the disc-shaped plate that actuates the switch when the weighted centrifugal arms are at rest.

After reassembly, make sure to locate the two oil fill caps (see the yellow cap in the photo). There is one above each bushing. So there is one on the front cap and the rear cap.

Auto part Technology Rotor Electronic device Machine


Remove the oil fill caps and fill with the same oil. Give it time to soak into the felt. Spin the shaft by hand for at least several seconds to ensure proper dispersion of oil. Add another drop or two if needed then reinstall the fill caps.

Auto part Technology Electronic device Machine Electric motor


Test the motor - first by rotating the shaft by hand to verify that there are no binds - then reattach the belt guard mount and pulley.

Pump Machine Technology Electronic device Electric motor



You should be back in business.

NOTE: If this does not solve your problem then the capacitor (mounted under the metal cover the bulges on the outside of the motor frame) is most likely at fault (barring a shorted or open winding or thermal fuse). Inspect it to see if it's blown apart or has bulged at the end or split. If the capacitor its not visibly damaged you may have to test it with a capacitance meter or replace it to verify. If the capacitor is the problem, however, the motor usually will not start with the help of a thumping. I already knew the centrifugal switch contacts were the problem, so I skipped that step in the tutorial.

If the capacitor is bad, make sure to replace with with the SAME value. In many applications, one can replace a capacitor with a slightly different value if there is no other option. But you really want the same value, type and voltage rating when replacing a motor start "cap" (capacitor). It is critical for the cool, efficient running of the motor.
 

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where's my table saw?
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Nice post!

Useful info and good presentation and photos. thanks :thumbsup:
 
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I wood if I could.
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Discussion Starter · #7 ·
By the way, this motor was reinstalled shortly after posting this thread and it is working perfectly and starting effortlessly every time. It sure is much cheaper to repair than replace.
 

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TheShadeTreeWW
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Thank you Steve!! This is for sure a bookmark!:yes:
Smokey
 
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nice job steve. we should make mention that when contacts are new, they have a specialized coating that resists deterioration caused by the arcing of contact closure/opening, usually containing some amount of silver. this deterioration is happening with every switch operation. the cleaning of the contacts is a good temporary fix. however, the abrasive cleaning removes more coating, as well as the corroded build-up on the surface, likely getting down to bare copper.

the motor will work, however the contact failure will come sooner next time, and next time.... btdt. best solution is to replace the contacts. steve would also be the guy for the best tutorial on that!
 

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Discussion Starter · #12 · (Edited)
nice job steve. we should make mention that when contacts are new, they have a specialized coating that resists deterioration caused by the arcing of contact closure/opening, usually containing some amount of silver. this deterioration is happening with every switch operation. the cleaning of the contacts is a good temporary fix. however, the abrasive cleaning removes more coating, as well as the corroded build-up on the surface, likely getting down to bare copper.

the motor will work, however the contact failure will come sooner next time, and next time.... btdt. best solution is to replace the contacts. steve would also be the guy for the best tutorial on that!
You are absolutely correct. That's why I use a contact burnisher. Yes, it still removes a minute amount of material, but it's not nearly as aggressive as a regular file. But 300-600 grit sandpaper would work as well. (600 is closer to the burnisher)

And I hear you about the fact that replacement is best case option. But, frankly, unless the contacts are burnt to hell, restoration like this is should hold up for years. Yes, it may fail again slightly sooner than brand new contacts would. But we're not talking failure on the scale of months. We're more likely talking years.

Depending on usage, obviously, I wouldn't expect trouble from those contacts again for - dare I say - five years or more. Especially since the contacts have never been treated and they showed little arc burn or pitting. I've owned this saw for a year and a half or so. The previous owner had it for a lot longer than that. I've restored at least 10's of thousands of switch contacts (so far) in my career of electronics repair. Enough to know that calling this a "temporary fix" is really selling short what has been done.

However, if the contacts were badly damaged "temporary fix" would be more a accurate description. Even then, it's not necessarily a short-term fix. Replacement is always "best". But it's not always the practical nor necessary solution.
 

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please don't take offense, as none was intended. when i said btdt, it was because my last bandsaw exhibited this problem after a few years of heavy use. after my contact cleaning, it lasted mabye 6 mos. then less, then less.
 

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Discussion Starter · #14 ·
please don't take offense, as none was intended. when i said btdt, it was because my last bandsaw exhibited this problem after a few years of heavy use. after my contact cleaning, it lasted mabye 6 mos. then less, then less.
No offense taken. Sorry if I came off that way. You did raise a valid point. It really all depends on the current state of contact wear. There is certainly a point where they can be shot beyond what mere servicing is going to solve.
 

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Wood Jedi
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I did electric motor repair for 10 years professionally. Not a bad tutorial there, I was dreading what you were going to put in for oil on them brass bushings. And you did right...a Light Weight, NON-DETERGENT oil..like a SAE 30 or 20 is prefered. Reason is, there's a detergent in regular motor oil and stuff like WD-40, that's the WORST stuff you can put in a motor with sleeve brg's like that. Eat's them right up..literally...

And good info with the Start Cap, make SURE it's the same MFD's and Volts...I'm thinkin' that one was a 120v maybe like a 180 or so MFD? The Capacitor is ONLY in the circuit during the START of the motor, when the switch inside opens, it takes the capacitor out of the circuit. Most of the time when the motor "growls" or "hums", it's because that start cap is bad, or there's an open in the start winding. And as one guy stated, try not to file or clean the points up, they'll work just fine...if they're bad, replace the switch. There's nothing too it, just a couple of screws, and make sure to label your wires and write out a diagram. :)

Make sure you get it cleaned out good...most motors on saws are ODP or Open Drip Proof motors, which means they suck in EVERYTHING...lol a good, parden my french, blowjob works wonders! lol You don't even have to take it apart to do this every couple of months, just grab your air hose, and with the motor NOT RUNNING, blow in the motor to get rid of the dust, this will keep it COOL. If it's packed with saw dust, air can pass through, and you risk overheating, or even burning up your motor..and worst case scenario, catching fire to the saw dust in the motor after the windings blow. It's just one added precaution...I actually blow out ALL my power tools weekly...used or not..:p

Also a good thing to know, when taking off the endcaps/endbells, if the side with the shaft doesn't come off EASY, it's most likely got a burr on it...DON'T FORCE IT, you'll score up your bearing since it's very soft metal, and that's not good...most know to just take some fine sandpaper or a small file, and take off the burr...
 

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Part of the reason some contacts don't last long after burnishing is that they may have previously gotten hot enough to cause partial loss of spring tension, causing poor contact when closing, leading to excessive arcing, which in turn causes further deterioration.
 

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Hey Steve I am also having trouble with a motor I have a thread
http://www.woodworkingtalk.com/f2/rewiring-tablesaw-help-please-49060/ What I was wondering is there another way to test the capacitor other than buying the meter that you mentioned. I'm going to take it all apart and clean it but any advice you could give me would be very helpful
 

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Discussion Starter · #20 ·
You could try taking it to an electrical or HVAC repair service and asking them to test the capacitor. Sometimes the capacitor will show visual signs of physical deformation. Also, replacing a bad capacitor can only be a temporary fix if the centrifugal switch is bad or sticking closed. That situation can burn a new cap right back out. I worked on a bench top Craftsman bandsaw (which I stil have stashed away) that kept burning up new capacitors. It was due to a centrifugal switch that had fused closed so that it never disengaged the start windings.
 
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