Fw: Re: SB-series friction dial drive

[Sandy and Kees Talen]

I guess I'm missing something here about rubber bands to repair SB
series drives. The only two drives I know about are the dual Jackson
Bros ball verniers as used on the SB-104, HW-101, etc and the pinch
rollers as used on the SB-301, SB-102, etc

The pinch rollers slip if there is not enough friction between the
beryllium
copper pinch roller and the tapered edge drive ring attached to the
plastic
dial. There should only be enough force between the tapered drive ring
and the pinch rollers to prevent slipping. The pinch roller should
definitely
not be visibly "spread apart", and absolutely not "pushed on all the
way".
I believe the gap between the two disks (drive removed from the SB-xxx)
should be between zero and approx .002" to work properly.

One cause of slippage is due to the drive ring being able to move
perpendicular to the shaft and not stay centered. This occurs if the four

mounting tabs are improperly installed or if the plastic dial has split.
One of the "inevitable" age/stress cracks which originate at the hub
may have made it out to the the edge of the dial. The ones that make
it out to the edge will usually be at the weakest points (where the drive

ring attaches) ....at "15", "40", "65", or "90".

Another possibility is that the beryllium disks are spread apart too far
or
cracked. Seems like the spacer between them could be filed down to
bring the disks together (the shaft would have to be filed the same
amount
or a shim installed under the outer washer to allow tightening). Cracked
disks would have to be replaced with something.

73s  Kees K5BCQ


--------- Forwarded message ----------
From: rayfri <rayfri at NETWORLD.COM>
To: HEATH at LISTSERV.TEMPE.GOV
Date: Wed, 2 Jan 2002 11:16:29 -0700
Subject: Re: SB-series friction dial drive
Message-ID: <3C334E7D.62C31D31 at networld.com>
References: <20020102.090923.-145611.5.k6uuz at juno.com>

Leafing through an old QST a while back I came across a nice little fix
for the SB drives if they start slipping.  The author said he took a
small
rubber band and wound it a couple times around the area between the two
discs to increase the diameter in there.  That increased the friction on
the

dial and it worked great.  Probably wore on the rubber band, but with
such
a simple fix, if you had to do that even every year, it would be no
problem.

ray  wa7itz

Ed Richards wrote:

> Hi Murray;
>
> I make my own from parts commonly available from your local hardware
> store. Materials needed are: (A) 2 ea 3/8" sheet metal lock nuts. These
> are beveled around the outside. (B) 1 ea 1/4" ID by 3/8 " OD rubber
> grommet, and (C) a length of 1/4" shaft. I use the excess shaft cut off
> of Radio Shack volume controls.
>
> Place the two lock nuts together with the beveled sides facing out.
This
> forms a "V" around the outside to engage the ring on the dial. Force
the
> grommet into the hole in the center, and one end of the shaft into the
> grommet. I have made several and they work good. Of course, the rubber
> wont last forever, but neither did the original !
>
> 73,
>
> Ed Richards
> On Wed, 2 Jan 2002 11:11:38 -0500 Multi-Volti Devices
> <multi-volti at SOFTHOUSE.COM> writes:
> > Hello and Happy New Year:
> >
> > Some time ago I requested help in the form of measurements for the
> > SB-
> > series dial drive planetary pressure discs (what else do you call
> > them?). I'll guess they're made of beryllium copper and they
> > eventually
> > crack.
> >
> > I am trying to source them, and either measurements, or ideally a
> > dud
> > pair you've given up hope on I could submit for analysis would be
> > even
> > better.
> >
> > I do not have any SB-gear myself.
> >
> > Murray
> >
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