[ARC5] [Milsurplus] BC-348 Backlash Again

[WA5CAB at cs.com]

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