[TowerTalk] Bearings in Rotators

[Jim Lux]

At 08:19 AM 10/24/2005, AA6DX - Mark wrote:
>Hello TTers ... just musing ... all the CDE / Hy-Gain rotators I have taken
>apart for the first time had room for a lot more ball bearings than came
>with "stock".  Years back, I went to the Bearings store locally and stocked
>up, and every time I put a rotator back together, I filled the race, within
>the plastic holder.
>What is the consensus on this practice .. why would you NOT do that .. and,
>of course, why does NOT the manufacturer ... it seems like such a
>no-brainer, but there must be a reason, other than $$$   ????    73, Mark
>AA6DX

I suspect it makes NO difference for a low duty cycle application like a 
rotator.

For things that continuously rotate, there are some peculiarities in how 
the balls roll along the race that make certain numbers of balls better 
than others.  For instance, they tend to stack-up next to each other, then 
spread apart.  This behavior results in different vibration patterns, some 
of which are "worse" than others for wear and life.  I think that the 
number of balls and/or the filling ratio affects this. But this was for a 
space application with very precise tolerances and life requirements (not 
to mention running in a vacuum) with people who obsess about every little 
funny noise or wiggle in the torque curve.

Some bearings have a spacer that holds all the balls (or rollers) at 
particular distances. Bearings that that have a consistent radial load 
might also perform better with certain numbers of balls in the race.

Neither is probably the case for a rotator.

You might try calling Fafnir or King Bearing and asking one of their 
applications engineers.

I'm just guessing here.. It would be interesting to know the "real story".

Jim, W6RMK