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  #1  
Old 03-09-2013, 02:08 AM
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Electric motor repair - Rigid table saw

Oh boy - the Home Depot Rigid 10" table saw looked good so I bought it - this about 8 or 9 years ago. I should have checked the brushes sooner. Oops. Started smoking the other night. Not sure what set it off, perhaps the brushes got too short and were no longer making good pressure so it started arcing. There was still brush left - both sides, in the past I've seen the brush go completely, just the holder pressing against the commutator.

At any rate, some of the brush holders melted. I figured I could salvage them but now I'm not sure. Turns out the exact replacement brushes and holder are no longer available. Oh boy. I got some that are wider but a tad thinner . - I'm hoping to make them work. A replacement motor would cost around $500 (!?) about the cost of a new saw. Problem is, it seems some of the burned out plastic also supported the brush somewhat. Without it, not sure it will stay stable enough to run.

Long story short (too late for that) I thought to replace some of the burned holder with some thin brass plate I had, pretty thin, about .015. Turns out a layer of that on each side makes for proper snugness, thickness wise, for my new jury rigged brushes which I sanded down to 1/2 wide, like the old ones. I managed to get it in place and soldered in place (see photo - the one on the right. Now here's the possibly dumb part: I can find no info on how hot brushes and their holder get in normal use. This thing melted part of the plastic on the holder, which is not your normal plastic, but it was arcing. Am I an idiot to think I can get solder this close to the commutator? Some of that melts, it will get on the commutator, and would probably really be history, instead of only halfway to it right now.



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  #2  
Old 03-09-2013, 08:53 AM
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If an electric motor starts smoking a coil has shortend.
Unfortunately that is not repairable, you can only replace the motor or the saw.

The sympoms of a worn brush are:
1- some lighning effects
2- power loss

IF the brush doesn't make good contact it can't conduct enough electicity, so it can't smoke (required a lot of current)

A shortend coil gives sunndenly a lot of (not very healty) smoke, and melts the brushes.

Electic tools for home use are not made for contimuous use, usually 10 minutes use and 50 for cooling down. Professional tools have a much better work cycle.
If you overheat them they will burn out.

Rob
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Old 03-09-2013, 11:09 AM
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I wouldnt be so pessimistic - I've seen motors smoke with low/broken/worn brushes before. Usually you'll see that the commutator/slip ring gets burn marks (if thats where the sparks/smoke were from)

use "crocus cloth" (or >800 grit sandpaper) to polish those surfaces back to a very smooth, bronze finish

Normal solder (eutectic or 60/40 should melt at 360-something degrees
Solder - Wikipedia, the free encyclopedia

Most industrial motors (single speed, 3600 or 1800rpm, any voltage from 480v to 13,000v) have high temperature alarms in the 170F-270F range - above that you are hot enough to deform the windings. I have no idea how much your 120v motor is like this (what kind of glaze/insulation, winding thickness and alloy etc.)


I'm afraid this isnt helping you much - 270F and 360F are kinda close. remember that at 212F water will boil off if you hit the motor with a drop (obviously not a stream of water). IIRC you can hold something at up to 130F or 140F depending on how baller you are

That being said - I'd solder it and make it run. YOLO

-John
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  #4  
Old 03-09-2013, 12:49 PM
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Quote:
Originally Posted by Rob Pruijt View Post
If an electric motor starts smoking a coil has shortend.
Unfortunately that is not repairable, you can only replace the motor or the saw.

The sympoms of a worn brush are:
1- some lighning effects
2- power loss

IF the brush doesn't make good contact it can't conduct enough electicity, so it can't smoke (required a lot of current)

A shortend coil gives sunndenly a lot of (not very healty) smoke, and melts the brushes.

Electic tools for home use are not made for contimuous use, usually 10 minutes use and 50 for cooling down. Professional tools have a much better work cycle.
If you overheat them they will burn out.

Rob
Not sure what the coil is. My only clue on the smoking was the major sparking coming from the commutator area - this I discovered after it started smoking. Also, the burnt and melted plastic in the brush holders. I hadn't been using it that long before it started smoking. Maybe 10-15 minutes.

I have gotten a lot of good use out of this saw. I should have been more astute about checking the brushes sooner. I'm in the process of checking my other major tools.
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Old 03-09-2013, 12:59 PM
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Quote:
Originally Posted by Angel View Post
I wouldnt be so pessimistic - I've seen motors smoke with low/broken/worn brushes before. Usually you'll see that the commutator/slip ring gets burn marks (if thats where the sparks/smoke were from)

use "crocus cloth" (or >800 grit sandpaper) to polish those surfaces back to a very smooth, bronze finish

Normal solder (eutectic or 60/40 should melt at 360-something degrees
Solder - Wikipedia, the free encyclopedia

Most industrial motors (single speed, 3600 or 1800rpm, any voltage from 480v to 13,000v) have high temperature alarms in the 170F-270F range - above that you are hot enough to deform the windings. I have no idea how much your 120v motor is like this (what kind of glaze/insulation, winding thickness and alloy etc.)


I'm afraid this isnt helping you much - 270F and 360F are kinda close. remember that at 212F water will boil off if you hit the motor with a drop (obviously not a stream of water). IIRC you can hold something at up to 130F or 140F depending on how baller you are

That being said - I'd solder it and make it run. YOLO

-John
I'm tempted to solder the other one and give it a go. If it was consistently hot enough to melt solder, I don't think the plastic in the brush holders would last that well that long.

This motor may be history at any rate. The commutator had two of the bands that were raised slightly. Who knows what came first: raised bands causing sparking or shortened brushes causing the sparking/heat that lead to damage of the holders and commutator. I've filed the commutator back to as close to round as I can determine. I've polished it with 600 - I guess you're right, I should get some 800 and 1000 paper and take it to that range.

I'd really like to get some more life out of this. I don't have too many spare $500 bills right now.
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  #6  
Old 03-09-2013, 01:53 PM
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If you find that the DC motor is shot I'd most certainly look about for a second hand replacement. Second hand DC motors are quite cheap here in Holland - not as cheap as a 3 phase motor... but none the less...
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  #7  
Old 03-09-2013, 08:12 PM
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Quote:
Originally Posted by cmac2012 View Post
Not sure what the coil is.
A coil is one of the windings (attached to the copper bars).

Worn brushes give sparks and hard starting/low power.
Nothing to serious, I have never seen a worn brush destroying a motor.

If it really smoked most likely one of the windings has shortened. Unfortunately not repairable.
A option is a replacement motor. Sometimes they are easy to find.

Rob
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Old 03-09-2013, 08:28 PM
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That's what we get for being glutted with cheap Far Eastern crap motors. In the past, you could have brought the motor to a shop to rewind it.
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  #9  
Old 03-09-2013, 08:49 PM
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cmac,

Do you have any documentation from when you actually bought the saw? With warranty information?

I have seen it claimed that, at some point in time, some of the Ridgid power tools came with a lifetime warranty.

Depending on when you purchased, it might instead have been eligible for their "Lifetime Service Agreement" - which requires registration, and only applies to the original owner. See here: Ridgid Power Tool Warranty.
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Old 03-09-2013, 11:17 PM
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Quote:
Originally Posted by spdrun View Post
That's what we get for being glutted with cheap Far Eastern crap motors. In the past, you could have brought the motor to a shop to rewind it.
And it would only cost twice as much as a new one from the far East

Surely new motor is available in an easier way... like a washing machine on the roadside on garbage day
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  #11  
Old 03-10-2013, 01:45 AM
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Quote:
Originally Posted by Eskimo View Post
cmac,

Do you have any documentation from when you actually bought the saw? With warranty information?

I have seen it claimed that, at some point in time, some of the Ridgid power tools came with a lifetime warranty.

Depending on when you purchased, it might instead have been eligible for their "Lifetime Service Agreement" - which requires registration, and only applies to the original owner. See here: Ridgid Power Tool Warranty.
After reading the warranty page, I think I'll be a little more conscientious about product registration. Most of those forms that come with tools have a huge questionaire asking what sort of hobbies you're into, how much you make, etc. I had come to believe that it was all fishing for marketing info.

I looked in my files and miraculously found the receipt. I don't recall registering for any service agreement. They might be hurting if I had as the brushes are not made anymore. A new motor goes for about $480. I was a tad high on the price. Not sure if I can buy a decent 1 horse motor and fit it in. I saw a vintage Rockwell on Craigslist:

Vintage Rockwell table saw

This is the way tools used to be. You bolt on a motor and hook up the belt. I think maybe the bench style Ridgid still do this, but mine is a semi-portable unit, good design all in all, you collapse it down and roll it away. Has a slide out fence bracket, goes out to about 25".

The armature has a sort of hypoid pinion gear on the end of it with a bearing below it. It fits into the carriage and bolts on with the stationary elec. mags, etc. Not sure how I could put another motor into it. One thought that comes to mind is to mount a pulley on the armature (if it proves unsaveable) and mount a motor next to it. Probably couldn't fold it up anymore. It's a long shot.
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Old 03-10-2013, 04:38 AM
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My neighbor at my warehouse/shop space is a metal fabricator and machinist. He thinks I'm OK with the solder and he puts the consensus over the top. I've gone to some lengths to save $500 here. I prepared a little jig to place the armature in and spin it with compressed air. Has bearings attached on both ends so it was easy. I started with 320 wet or dry paper on the commutator and and went up to 1000. Looks and feels pretty smooth. Photos before the buffing - what was I thinking.

The two loose copper bits in the photo are the connectors power hooks up to. I need to pry up the tabs and stick the new brush wire in, this with the new springs in betwixt. Here goes . . .
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Last edited by cmac2012; 08-18-2013 at 02:14 PM.
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  #13  
Old 03-10-2013, 04:41 AM
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The gouges in the armature in this picture look like the bearings have gone too



are you planning on replacing them?
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  #14  
Old 03-10-2013, 10:41 AM
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You are really attached to your saw.

I'm no expert and wasted lots of time tying to fix electectric motors until one of my very technical friends gave me a quick course.

He had some practical tips:
1
Never touch the cummulator, maybo with a copper brush, but not with sandpaper or a file.
The only way to get it smooth again is with a percision (expensive) lathe. The tolerances for roundness are measured in micrometers. If it off the brushes will start to float, produce sparks and wear out very quickly. Also most of the power will be lost.
2
The only thing that can be repaired on these (I think they are called Universal motors in enlgish) are the brushes and bearings.
3
Wear on the cummulator is ok, it doesn't have to be smooth, only round.
4
Smoke is bad, in 99.9% of the cases the motor is toast. Be carefull with the smoke, very unhealthy.

There are a lot of different types of electric motors, each with specific advantages and disadvantages.

If you have a brushless motor like used in a fan, never let it run without the fan attached. It will spin out of control and can even disinterate.

Rob
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  #15  
Old 03-10-2013, 04:24 PM
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Quote:
Originally Posted by Stretch View Post
The gouges in the armature in this picture look like the bearings have gone too



are you planning on replacing them?
No, the gouges on the armature were factory made for balancing. The bearings are in good shape, but the motor is toast.

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