Disc grinder Repairs

[KWESHAZ]

I have just decided to keep myself busy during this lockdown by carrying out some 21" Metabo disc grinder repairs.I had 3 broken grinders and out of the 3 decided to atleast get the best components out of the 3 and assemble or come out with one.So I did tests on the field coils,armature (rotor) & switches and got the best out of the 3 to assemble one.On testing the assembled grinder I realised there is a lot of sparking on the brushes and commutator.I am kindly asking for assistance from those that might have experienced this before and solution to this problem.

 

[D tj]

The armature may be shot, the brushes sticking...not moving freely or badly shaped/worn and not mating well to commutator or worn too short.
Commutator may be badly worn : ought to be parallel to shaft axis. and smooth.....file and or sandpaper smooth and flat. Check no copper dust / particles between segments before refitting !!!!!!!!! ....Vital !!!

Most likely armature shot: examine the wire to each commutator segment look for signs of arcing blueing...discolouration through heat.

 

[KWESHAZ]

Thanks D tj for your contribution.I have checked the condition of the brushholders,brushes, switches , field coils and armature and all seem to be good.I even fitted another brush holder set which appeared to be in a better condition and fitted new brushes but the sparking on the brushes is terrible.I have now done 3 tests on the two armatures and attached are the results.I did a commutator 180 degree test, bar to bar test and insulation resistance tests.From those results well Armature 1 is suspect from the 180 degree test but what about Armature 2.

 

[D tj]

Ill send you a pm w my no , you are welcome to call me.

 

[KWESHAZ]

Thanks that will be great.Will be waiting

 

[D tj]

sent