[ARC5] Re: [Milsurplus] Dynamotor brushes

[J Forster]

AFAIK, there is nothing that will dissolve graphite. Can you remove the
opposite brush and push on the stuck one with a little stick?

Brushes are the asymmetrical, and designed to be put in with the curved end in
a specific orientation. Does the book say to insert them with the - or + facing
up?  If so, the markings might just be an aid for the mechanic, rather than an
electrical necessity, to reduce run-in time.

FWIW,
-John



Clare Owens wrote:

> 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