[R-390] Tooth Error

[ka9egw at britewerkz.com]

In my R390A required complete disassembly and cleaning of the RF geartrain.
Per accepted practice, I put it back together with the cams indexed for 7
+000.

Aligning the Geneva mechanism [which was cleaned in-place and hence not
removed from the RF deck] per the illustration in the Y2K manual, page 6-8,
shows the Geneva Drive intermittent gear and it's associated pinion set with
one tooth of the pinion at exactly 9 o'clock [and other pinion teeth at 7:30
and 6:00], with the clockwise of two teeth on the intermittent gear
immediately below the 9:00 tooth on the pinion.  When assembled according to
this drawing, the majority of bandswitch indexing took place on the 7-8
uppshift but there was also a significant amount on the 6-7 upshift with
corresponding issues with slug rack cam timing.

After numerous disassemblies and reassemblies, I was able to ascertain that
for my rf deck [YMMV], the proper indexing of the geneva drive intermittent
gear is as follows:

[1]  Meshed with the respective teeth exactly as shown on page 6-8 of the
Y2K manual.  What I'm trying to say here is page 6-8 does NOT show these
gears improperly meshed **to each other**.

[2]  The Geneva Drive intermittent gear, however, needs to be  <1/4 tooth
counterclockwise of the position shown, and the pinion needs to be <1/4
tooth clockwise.

How this was accomplished, was multiple removals and replacements of the
differential and the large brass double gear [installed in Step 10 of Scott
Seickel's excellent photo tutorial] to facilitate indexing clockwise by one
tooth the idler shaft large gear [installed in step 2 of Seickel's] that is
driven by the aforementioned "Step 10 double gear".  This will set the
Geneva Drive's interrupted gear very slightly [we're talking something
probably best measured in minutes of arc here] CCW of the position shown on
page 6-8.

I really hope I explained that right.  When finished, the tooth of the
Geneva drive pinion shown at 9:00 on page 6-8 of the Y2K manual, ends up at
a couple minutes after [clockwise of] 9:00 at 7 +000 Mc.

This is nowhere near a full tooth on the Geneva Drive.

With this minor correction, 90+% of all movement of the rf bandswitch takes
place on the 7-8Mc upshift and the remainder on the 8-9Mc upshift.

-----Original Message-----
From: Perry Sandeen [mailto:sandeenpa at yahoo.com]
Sent: Monday, August 30, 2010 11:49 AM
To: ka9egw at britewerkz.com
Subject: Tooth Error


Hi Brian,

You Wrote: I come to the inescapable conclusion that the drawing of the
geneva mechanism at 7+000 in the Y2K manual is in error by something less
than 1/3 tooth.

If you could please write up the problem and solution along with a reference
to the drawing I'll try to post a supplement or give to to W. Li to add to
his "Pearls" info.

Regards,

Perrier



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