[R-390] Another geartrain tidbit

[Barry]

I noticed the same thing.  Some of mine wobble just a bit, but not enough to
matter.  There is one (not a split gear) that drives the bandchange to the
crystal deck and the MC section of the VeederRoot counter that wobbles a bit
more than the others.  It doesn't really affect performance so I just
decided to leave it alone.

It's odd that some of the gears were manufactured to very precise standards,
but then some of the quality steps like the brazing of the hubs to the gears
didn't get a lot of QC.

Barry(III) - N4BUQ

----- Original Message -----
From: "John KA1XC" <tetrode at comcast.net>
To: "R-390 reflector" <r-390 at mailman.qth.net>
Sent: Friday, March 11, 2005 12:48 PM
Subject: Re: [R-390] Another geartrain tidbit


> Interesting find, that is one of those arcane problems which are only
> discovered only by those who tear down the gear train.
>
> The 390A currently on the bench has what I eventually started to call the
> "RF deck from hell" as it had so many problems. One of those involved the
> split gears, and *none* of them moved. As you discovered, the two gear
> halves had to be compressed so much for the snap ring to take hold that
the
> whole thing bound tight. Upon inspection each was found to have one of its
> gears out of  "flat" and I proceeded to fix them in a similar fashion to
> what you described.
>
> All seemed OK until the gears went back on the shaft during reassembly and
> then I noticed they were now wobbling when rotated. Took them off and
apart
> again and gave them a closer look and what I discovered made me feel
sick -
> the center hubs had been soldered/brazed into the gear crooked!
>
> These were obviously defective parts, and this deck likely had this
problem
> since day one out of the factory. My fix was to pick up some replacement
> gears from Fair and things went back together smooth after that. The RF
deck
> was a '63 Teledyne BTW.
>
> 73,
> John
>
>
>
> ----- Original Message -----
> From: "Barry" <N4BUQ at aol.com>
> To: <r-390 at mailman.qth.net>
> Sent: Thursday, March 10, 2005 11:57 PM
> Subject: [R-390] Another geartrain tidbit
>
>
> > While cleaning and reassembling one of the split gears tonight, I
> discovered
> > something interesting.  No matter how much I wetsanded the faces of the
> > teeth, when I reassembled the halves the assembly would bind and the two
> > halves would not move freely against each other.  I had this happen (to
a
> > lesser degree) on another gear set and I was determined to figure out
why
> on
> > this one.
> >
> > It turned out that the half of the gear that has the hub brazed onto it
> had
> > a slightly convex shape.  When I pushed the snap ring down into its
> groove,
> > it was applying pressure on the flat gear forcing it against the
non-flat
> > half and only the outer edges near the teeth were pressing together.
> Laying
> > a straight edge against the side of the gear confirmed this.  It was
about
> > 0.015" to 0.020" out of flat.
> >
> > I was able to use a steel disk (with a hole in it just a little smaller
> than
> > the OD of the gear and a neoprene hammer to flatten the outer gear.
Well,
> > actually, the gear material was a lot softer than I anticipated and I
> ended
> > up getting it convex in the other direction; however a few taps with
> another
> > setup and I was able to get it flat again.
> >
> > Now the two halves rotate quite freely against each other with the snap
> ring
> > in place and the antibacklash springs are easily set to a tooth or two
of
> > tension.
> >
> > Just thought I'd pass this along.  It wasn't easy to see the problem
with
> > this one.
> >
> > Barry(III) - N4BUQ
>
>
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