[ARC5] Dynamotor brushes

[Clare Owens]

I'm in the process of fixing up the DM-28 dynamotors I bought at the
CC-AWA Conference a week ago.  One of them was essentially unused and
the grease softened up nicely with some light oil.  It ran fine for
1/2 hour last night, no trouble at all.  But the other one has seen a
lot of wear, lots of carbon powder in the housing, rough feeling
bearings and one LV brush is stuck tight.. Really tight.  I have
removed the LV end bell and while I was cleaning the bearings I
removed the brush holder and applied motor cleaner then soaked the
holder in Acetone and now have applied a lot of force in both
directions with no results except a little chipping.  I guess I'll
have to destroy it to get it out.

The good news is that I just looked in my box of very old brushes and
I have an envelope of unused spares for all four brushes.  The part
numbers on the envelopes match the parts list numbers for the brushes
for the DM-28 for the BC-348-H anyway.  This one was from an "O" but
should be the same, no?

But before I destroy this brush, does anybody have any other method to try?

Also this brings up the question:  Why are they so specific about the
positive and negative polarities of the brushes?  They have different
part numbers, there are plus and minus signs molded into the housings,
etc.

What difference could polarity make in a graphite brush?

Also, I just have to comment on the high quality of design and
manufacturing of these units.  The dynamotor innards I have seen over
the years all have been remarkable examples of how to build a device
that would work well under harsh conditions and last for many, many
years.  They make the insides of most of my modern electric tools look
like junk.

Thanks,

Clare  N2RJB