universal motor brush placed oblique
I have a very old vintage Black and Decker very heavy and heavy duty industrial angle grinder. All metal. Likely 1960’s. 9 inch, honest 13 amp. The switch is turned by a large vertical pin.
The brushes seems nearly new (almost full) but one of them is set at a very oblique angle. The brush housing is tightened by a screw that can be turned from the outside, from what I can tell. Apparently one brush housing has been rotated.
The tool still runs strong. Apparently the rotation of the brush housing occurred gradually and the brush at an oblique angle has taken up the shape of the armature (?) (I think what comes into contact with the brushes is the armature)
What should I do? Would the rotated brush gradually wear out the armature or is the brush so soft that the armature won’t be damaged, so I should just let it be.
Should I try to set the angle of the brush housing correctly and sand out the brush? Should I use a sanding drum the same diameter as the armature to create a profile on the brush? I can buy a new brush, but I have no idea if it is still available.
Edited 11/14/2007 12:06 am ET by woodenfish3
Edited 11/14/2007 12:08 am ET by woodenfish3
Replies
Fish, the carbon brush will not wear the armature apart from the normal wear that happens with use-it is relatively soft.
If it runs well with no abnormal arcing you could leave it be. Check to see if both brushes have the same amount of sparking/arc. Check to make sure that the brush housing cannot come out and contact the armature: if that happens the motor will be history.
If you decide to replace the brush hosing correctly the brush will need to be re-faced so that it fits the curve of the armature- so you will lose some length there, and it will be shorter than the other one. The curve is easily shaped- find something the same diameter as armature, wrap some 220 silicon carbide paper round it and shape the brush so that it makes good contact.You could use your sanding drum, carefully. Be sure the brushes are free to be pushed by their springs onto the armature.
Thanks Philip.
I will make sure that the small screw that can be turned from the outside is tight so that the hosuing won't rotate anymore. I will leave it be for now.
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