[ARC5] [Milsurplus] BC-348 Backlash Again

[Richard Knoppow]

----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: <Arc5 at mailman.qth.net>
Sent: Wednesday, August 22, 2012 10:01 AM
Subject: Re: [ARC5] [Milsurplus] BC-348 Backlash Again


> 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

     I am not familiar with this equipment but by any chance 
does it have an Oldham coupler?  These couplers can cause a 
lot of rotation play which may seem to be backlash. I've 
found on the Collins sets that do have Oldham couplers that 
they must be clamped together before tightening the set 
screws.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com