[R-390] Geneva Mechanism question

[Barry]

Paul,

Thanks for the advice.  I'll try to remember to watch that the bandswitch
gear makes good, clean transitions.

I placed a 0.003"-0.004" shim washer between the outer gear and the
sandwiched plate.  It seemed that with the outer gear riding directly
against the plate, I could detect a very small of drag.  With the shim
washer, it is very smooth; however, if this causes too much 'slop', then
I'll remove it.  Everything appears to be 'tuned' quite nicely here, though.

Thanks,

Barry(III) - N4BUQ

----- Original Message ----- 
From: "Paul H. Anderson" <paul at pdq.com>
To: "Barry" <n4buq at aol.com>
Cc: <r-390 at mailman.qth.net>
Sent: Tuesday, March 08, 2005 3:03 PM
Subject: Re: [R-390] Geneva Mechanism question


>
> 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
> >
>