[ARC5] ARC5 Digest, Vol 103, Issue 52

Wed Aug 22 18:38:32 EDT 2012

Yeah..a common enough problem with the 348..especially when re-fitting a 
removed tuning mechanism or transferring one from one rx to another..never 
quite fits exactly the same..the screws on the front panel that fix the 
panel to the chassis can affect the alignment of the mechanism that connects 
the tuning cap gears to the drive engagement..make sure that the panel 
screws are properly aligned and are tightened without stress..removing the 
variable cap and refitting or transferring to another set is also 
problematic as it is difficult to fit again exactly as it was in the first 
place..there is no play in any of the screws so the slightest stress can 
affect the meshing and alignment..most of them have a little backlash anyway 
and in my experience does not detract from enjoying their use..everytime you 
re-fit it it will be slightly different than before but keep doing it until 
you get the best you can..the different makers mechanisms are not 100% 
compatible but work ok

-----Original Message----- 
From: arc5-request at mailman.qth.net
Sent: Wednesday, August 22, 2012 6:01 PM
To: arc5 at mailman.qth.net
Subject: ARC5 Digest, Vol 103, Issue 52

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Today's Topics:

   1. Re: [Milsurplus] BC-348 Backlash Again (WA5CAB at cs.com)
   2. bc459 (Alan Morriss)
   3. Re: [Milsurplus] BC-348 Backlash Again (Kenneth G. Gordon)

----------------------------------------------------------------------

Message: 1
Date: Wed, 22 Aug 2012 12:35:49 -0400 (EDT)
From: WA5CAB at cs.com
Subject: Re: [ARC5] [Milsurplus] BC-348 Backlash Again
To: milsurplus at mailman.qth.net, boatanchors at theporch.com,
boatanchors at mailman.qth.net, arc5 at mailman.qth.net
Message-ID: <4ed74.1c8ca07e.3d666465 at cs.com>
Content-Type: text/plain; charset="US-ASCII"

Dave,

Any anti-backlash gear and worm pair that I ever saw has several times the
amount of rotation (throw) needed to remove any amount of backlash between
it and its driving worm gear (pinion).  If, when preloaded, there is still
backlash between gear and tuning knob, I can think of five possible reasons:

(1) loose set screws in shaft couplings or knobs.
(2) end float in the pinion shaft bearings (if that's your problem, then
the plastic tape must have side-loaded the pinion enough to force the balls 
to
the zero clearance point of one or two of them, which will pretty soon quit
working as the tape wears).
(3) weak spring.
(4) excessive torque required to rotate the capacitor shaft.
(5) excessive force required to rotate the movable gear.

Robert D.

In a message dated 08/22/2012 09:43:28 AM Central Daylight Time,
arc5 at ix.netcom.com writes:
> Working on getting a very nice BC-348 going for a friend.
> Backlash is a common problem with these sets.
> In this one, the backlash cause was between the gear
> on the end of the tuning capacitor and the pinion gear
> that drives it.  No amount of removing, cleaning,
> re-lubing and spring-retensioning corrected it.
> Couldn't see a non-destructive way to mesh the
> two gears tighter.
> The anti-backlish gear on the end of the tuning cap
> just does not have the "throw" needed
> to take-up the slop between it and the pinion.
>
> I cleaned-way all the oil and grease from the pinion.
> Cranked the tuning cap all the way closed.
> Then cut a strip of plastic electrical tape and fed it
> into the gear mesh point, cranking until I could grasp
> the end and bring it around, pressing the ends together,
> and then ran the gear back and forth to seat it.
> Used a soldering iron to remove the excess tape,
> leaving a little tab.
> This filled the slop and completely eliminated the backlash.
> Yes, the plastic tape will wear-out eventually.
> Does anyone know of a better and non-destructive
> product for taking the slop out of this mesh point without
> "poisoning" the lube in the tuning cap anti-backlash gear?
>
> 73 DE Dave AB5S
>

Robert & Susan Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

------------------------------

Message: 2
Date: Wed, 22 Aug 2012 18:00:15 +0100
From: "Alan Morriss" <mohawk at clara.co.uk>
Subject: [ARC5] bc459
To: <arc5 at mailman.qth.net>
Message-ID: <E10270D6CF9F4480B46F9007D89F8ADD at alan>
Content-Type: text/plain; charset="Windows-1252"

hello guys , i was fortunate to obtain what looks like a nice BC459 on ebay 
. it wasot too expensive at ?45.45 ($73.39) . this means that my search for 
a PA cover plate and bottom cover is scaled down . however i would still 
like to fit them to the tx to restore it .hopefully it will be around longer 
than i will ! alan

------------------------------

Message: 3
Date: Wed, 22 Aug 2012 10:01:19 -0700
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
Subject: Re: [ARC5] [Milsurplus] BC-348 Backlash Again
To: Arc5 at mailman.qth.net
Message-ID: <5035105F.29171.46CF2F9 at kgordon2006.frontier.com>
Content-Type: text/plain; charset=US-ASCII

On 22 Aug 2012 at 12:35, WA5CAB at cs.com wrote:

> Dave,
>
> Any anti-backlash gear and worm pair that I ever saw has several times
> the amount of rotation (throw) needed to remove any amount of backlash
> between it and its driving worm gear (pinion).  If, when preloaded,
> there is still backlash between gear and tuning knob, I can think of
> five possible reasons:
>
> (1) loose set screws in shaft couplings or knobs.
> (2) end float in the pinion shaft bearings (if that's your problem,
> then the plastic tape must have side-loaded the pinion enough to force
> the balls to the zero clearance point of one or two of them, which
> will pretty soon quit working as the tape wears). (3) weak spring. (4)
> excessive torque required to rotate the capacitor shaft. (5) excessive
> force required to rotate the movable gear.

Dave:

Adding somewhat to what Robert has listed above, it has been my
experience that if the tuning capacitor has a lot of drag, for any of a 
number
of reasons, backlash, even with the split-gear anti-backlash units, and
everything else (shaft couplings, end bearings) are correct, backlash will
never be acceptable. The main reason is excessive drag in the capacitor
itself, usually due to deterioriated lube, a misaligned main-shaft, or other
such things.

In your case, I would, if possible, remove the main-tuning cap and check to
see how hard it is to rotate. It should be rotatable with one finger.

Ken W7EKB

------------------------------

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End of ARC5 Digest, Vol 103, Issue 52
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