[R-390] Another geartrain tidbit

[John KA1XC]

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