[R-390] Geneva Mechanism question

[Paul H. Anderson]

Don't forget that these little guys are sensitive to proper spacing on the
shaft.  They may need very thin shims to get them to not rock so much that
the ball bearing slips enough that the band tuning switch doesn't make
definitive transitions from band to band going both forwards and
backwards.

I've run across a few in R-392's (and one R-390A) that had this problem,
and I also introduced this problem myself when I wasn't careful.

Paul

On Mon, 7 Mar 2005, Barry wrote:

> I've started reassembling the geartrain (yes, I work slowly with limited
> time).  Since I disassembled the Geneva mechanism, I started there.  When I
> disassembled it, I didn't pay too much attention to how it worked.  When I
> reassembled it, though, I was pleasantly surprised.  The Geneva mechanism of
> the subassembly is common enough (although the intermittent action of having
> different groups of triggering gears is a bit unique), but the other part is
> quite amazing too.
>
> The little ball bearing's action with the larger part of the Geneva
> mechanism is quite unique.  The ball bearing along with the accompanying
> slots and hole are a marvel to see in action.  It allows the main gear to
> make nearly two complete revolutions before coming to a hard stop.  I don't
> think I've ever seen anything quite like it.
>
> Does this part of the mechanism have a name?  It is perhaps one the
> cleverest part of the entire geartrain.  If you do decide to do a rebuild, I
> would definitely recommend taking this thing apart just to see how it is
> designed.  Mine had a bit of crud in the gears that needed to be cleaned out
> (and besides, it allowed me to polish the brass outer gear) and it really
> works smoothly now.
>
> Regards,
>
> Barry(III) - N4BUQ
>