[ARC5] Dynamotor Maintenance

[Mike Hanz]

As both Roy and Ken point out, there are many forms of graphite, John.  
I was specifically referring to carbon dust from the brushes, which is a 
harder material than pure graphite.  Roy's reference to a clay material 
rings a bell with me too.  Perhaps abrasive was a stronger word than 
needed - it has a polishing action that will wear high speed bearings 
out fairly quickly in steady service.

I am frequently reminded how much caveating (or maybe cavitation? :-) ) 
is needed when we talk about stuff on this list.  E-mail isn't the 
greatest medium for covering complex subjects.  Here are some additional 
caveats that came to mind after reading the morning traffic:

1)  The primary subject has been small dynamotors which had no forced 
ventilation, unlike the larger dynamotors (ART-13 and the like, as well 
as most of the rotary inverters by the end of the war.)  In that 
equipment, an open architecture with fans and impellers on the shaft 
blow quite a blast of air past the commutators and reduce the carbon 
dust problem to a degree.  The Navy took it to the logical extreme with 
shipboard equipment, a great deal of which had no end bell covers at 
all.  Just don't stick your fingers in the rotating machinery to test 
it...OSHA wasn't there to fiddle with the situation.

2)  In the late 1950s, bearing seals had vastly improved because of new 
materials, and I have an NOS DY-17A here from Robert Downs whose 
bearings has no capability of being serviced.  Like any machine, it 
needs to be cleaned and check occasionally, but it should have a longer 
time between servicing than the WWII counterparts.

3)  In the last few months, a list member sent me some photos of an 
amazing amount of wear on a commutator - the brushes had carved a deep U 
shaped valley across the commutator, and he said it was still running 
fine.  It's another reason never to say never about something.  There 
are always example of extreme punishment endured without whimpering.

4)  In rereading what I wrote last night, I want to make it absolutely 
crystal clear that I did not mean to reflect any disrespect for Wayne, 
nor suggest that he was wrong in any way.  I was grateful that he took 
the time to post the fascinating differences between the two manual 
revisions, and he obviously knows what he is doing -  his work on a 
dynamotor using "magneto grease" (small bearing grease) is a classic way 
of doing a job the "correct way" (if there is such a thing.  Some folks 
bristle at the thought...)  My closing thoughts were directed toward 
some stuff I've read on the ham radio reflectors, not to any of the 
inhabitants of this list - we collectively seem to have a lot more 
knowledge than the folks on those lists.

I hope that everyone was a wonderful Sunday,
  - Mike  KC4TOS

On 1/19/2013 11:15 PM, J. Forster wrote:
> I am puzzled by your statement that Graphite is abrasive, especially since
> it is widely used as a dry lubricant.
> Messy, for sure, but abrasive?
>
> -John
>
> ==============
>> 3)  Clearly this was a non-sustainable maintenance policy.  While the
>> binder doesn't wear out, and you can renew the viscosity level of the
>> lubricating oil that does the essential work in the bearing, you cannot
>> keep contaminants out, and carbon dust from the brushes is one of the
>> most abrasive contaminants around.