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

[Dennis Monticelli]

Mike,

Excellent info and helpful hints, Mike.  Thank you.  There is no evidence
of lubrication whatsoever on gears or worm, nor marks from hard knocks,
though with regard to the latter it could have happened and left no case
evidence. The anti-backlash gear set is free to operate as it should. I can
put a small screwdriver blade into the teeth and twist slightly to observe
the action. I will investigate which screws I could loosen to change the
mesh relationship per your recommendation.  Once I get that optimized, I
will put a drop of synthetic oil on either side of the worm near the mesh
point.

Dennis AE6C


On Tue, Jan 21, 2014 at 2:23 PM, Mike Hanz <aaf-radio-1 at aafradio.org> wrote:

> 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
>
>
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