[ARC5] lubricating BC-221 or LM freq meter gearing

[Mike Hanz]

On 1/21/2014 3:14 PM, Dennis Monticelli wrote:
> I have the LM version and while the freq knob turns freely I can feel every
> tooth engage and disengage; it's a bit rough.  As far as I know no
> lubrication was used originally (except for the shaft bearing which is not
> the issue) so the good news is nothing as gummed up.  But I wonder if
> judicious application of the right lubricant would make the tuning much
> smoother.  I did check the action of the anti-backlash and it is working
> correctly.  Has anybody tried applying lubricant to smooth the worm gear to
> anti-backlash gear interface?

The roughness, sometimes called "cogging", is frequently caused by two 
things:

1)  The failure of the anti-backlash gear to rotate smoothly in its 
bearing with respect to the primary gear, thus presenting a less than 
optimum tooth profile to the driving gear or worm, or

2)  a changed relationship between the driving gear and driven gear, as 
the result of a hard blow to the chassis or loosening of the mounting 
bolts, causing the mating teeth to either mesh more tightly or more 
loosely than they were designed to do.

The usual cause of #1 is dried lubricant between the anti-backlash gear 
and its nested primary gear, resulting in the two being effectively 
glued together.  That doesn't appear to be the case with Dennis' unit.  
Normally you shouldn't grease those two mating surfaces at all - the 
mating conditions of infinitesimal movement normally generate no wear 
whatsoever unless you're power driving it back and forth 24/7/365.  
Unfortunately, we guys have always been taught to grease everything in 
sight...it's been a right of passage to manhood or something, so you 
will run into the situation from time to time.  Since more is better, 
the problem often comes from putting too much grease on the teeth and 
the passage of a few decades.  So, if it's a sticky mess, you'll have to 
take the assembly apart and clean it in mineral spirits.  The one part 
that does require a lubricant is the worm, but that only requires 2-3 
drops of oil every couple of years, and allow that to transfer to the 
driven gear teeth naturally...Mobil I or other synthetic is excellent 
for that, since its lubricity is more stable over time than petroleum 
based lubricants.

For #2, the easiest solution is by trial and error, loosening the screws 
on either the capacitor or worm assembly and tapping one or the other 
back and forth to change the mesh relationship of the mating gears.  
You'll find a "sweet spot" where there isn't any cogging as you turn the 
tuning dial, and that's where you want it to stay.  There is a certain 
art to the process, since tightening the screws will often change the 
mesh, so you'll have to do a bit of tightening and loosening before it 
finally settles into the right spot with the screws tightened.  Try 
clamping parts in a milling machine for a few years and you will 
appreciate the process even more. :-)   I've run into a couple of 
situations where .001-.002" shimming was required, either because a 
replacement part was installed or the instrument had been dropped and 
the case slightly distorted.

     73,
  - Mike