Announcement

Collapse
No announcement yet.

For one of you motor gurus.

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • For one of you motor gurus.

    The other day I noticed that my Milwalkie 4.5 inch angle grinder was not spinning up to speed and was making an odd noise. Today I took it apart and checked the commutator. Most of the communtator was a light chocolate brown. One palce looked burent. I cleaned the communtator put it back togeather. Still had the noise. Opened the motor back and run it with the cover off. There was a lot of sparking under one of the brushes. Any ideas as to what else to check for and or a fix? My guess is that one of the windings has gone bad and I now have a piece of junk.
    Charlie.
    Don\'t ask me to do a dam thing, I\'m retired.
    http://home.earthlink.net/~kcprecision/

  • #2
    Maybe you need new brushes? One of the springs that hold the brushes against the commuator is bad?

    Comment


    • #3
      Either the brush is sticking in its holder or the brush is shot and needs to be replaced. Work the brush in and out to ensure free movement, check them for length, etc

      Comment


      • #4
        If you have sparking under one brush, my guess would be to change the bushes.

        Comment


        • #5
          Check for continuity between the commutaor bars and the armature shaft,if any of the bars show continuity then the bar or its winding is shorted to ground(new grinder time)
          I just need one more tool,just one!

          Comment


          • #6
            Charlie:

            IF the brushes are servicable? try taking a common pencil eraser and running unit while holding eraser against the dirty commutator as it turns. If possible. I have cleaned large Dc motors this way. The chlorine atmospheres I used to have to endure would corrode a dc motor in just a bit. A new drill was shot at two months old. The pretty shiny commutators fared about the same. The gargling sound is probably not a good sign, probably a dead bearing or gear train. It might be a dead spot on there tho. If it is a model still available www.grainger.com has parts you can mail order. It is worth fixing. I personally like the milwaukee brand tools. Price all the parts before you order them if possible. They can be pricy.

            Watch your fingers, And don't get shocked. The tool is not worth that.

            Shaper still running?

            David

            Comment


            • #7
              I checked the brushes they are down in the holders about 1/4 inch. They also seem to be free, (move up and down). One brush seem to be doing all the sparking. I had forget about checking the the commutator bars to ground which seems so basic.

              The eraser is a good point. We use to clean the collector rings and commutators with a pumice stone.

              Now days it is just about as cheep to buy new as to try and repair the tool but will check and see befor doing anything drastic.

              Thanks for the help guys.
              Charlie.
              Don\'t ask me to do a dam thing, I\'m retired.
              http://home.earthlink.net/~kcprecision/

              Comment


              • #8
                Brushes have a lead wire pressed into them, and sometimes when the brush is short, that wire can begin touching the commutator. There could be some brush left, but if this is happening, replace the brushes right away. Maybe the damage to the commutator is slight at this point, but it will get far worse in short order.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                Comment


                • #9
                  Rotate the motor by hand and try to determine if the armature may be binding anywhere on the permanent magnets. It's a pretty close tolerance here and if it's touching it can explain what you've described - even the excessive sparking at the brushes. Tool might have been dropped and the bearings are somehow misaligned. A magnet could also be broken or loose and rubbing against the armature.

                  Comment


                  • #10
                    I have checked the brush wires and they are loose but one looked like it could have been pinched and not let the brush down as it wore.

                    The motor turns free so that is not the problem.
                    Charlie
                    Don\'t ask me to do a dam thing, I\'m retired.
                    http://home.earthlink.net/~kcprecision/

                    Comment


                    • #11
                      Did you mean that only a quarter inch of brush is still existing?

                      When the brush gets to where the amount in the holder is the same as the width of the brush, it starts to bind and not sit straight. In that case, replacing brushes is in order.

                      Milwaukee has turned into a junk brand in many cases (IMO) , but is still pricey enough to warrant brush replacement. That's if nothing else is bad. When a shaft in our drill motor sheared, we found it was cheaper to toss it and get a Makita.
                      1601

                      Keep eye on ball.
                      Hashim Khan

                      Comment


                      • #12
                        Just a chance you've overheated the brush springs. They lose temper, so higher resistance, so more heat, more de-tempering.....
                        Should be cheap enough to replace brushes.
                        Lin

                        Comment


                        • #13
                          J; no the brush is only down from the top of the holder about 1/4 inch.
                          Swarf the brush spring still had tension on it but I do need to check to see if the brush is seating solid aginst the commutator.
                          Charlie
                          Don\'t ask me to do a dam thing, I\'m retired.
                          http://home.earthlink.net/~kcprecision/

                          Comment


                          • #14
                            If the arcing seems to be at a particular spot on the commutator, you very likely have an open armature winding. Look very carefully where the wires attach to the commutator at the burned spot and you may be able to resolder or splice it.
                            Don Young

                            Comment


                            • #15
                              <font face="Verdana, Arial" size="2">Originally posted by Don Young:
                              If the arcing seems to be at a particular spot on the commutator, you very likely have an open armature winding. Look very carefully where the wires attach to the commutator at the burned spot and you may be able to resolder or splice it.</font>

                              If it runs unevenly, and you see that sparks seem to streak around the commutator when its running that's another point in favor of the above.

                              If there are positions of the armature in which it will not start, that almost nails it.
                              1601

                              Keep eye on ball.
                              Hashim Khan

                              Comment

                              Working...
                              X