View Single Post
Old 03-29-18, 08:51 PM
  #7  
AnkleWork
Senior Member
 
Join Date: Jan 2013
Location: Llano Estacado
Posts: 3,328

Bikes: old clunker

Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 540 Post(s)
Likes: 0
Liked 25 Times in 15 Posts
Originally Posted by sweeks View Post
I'll agree that caged bearings are easier to work with; that's one reason they are used in bicycle manufacture, where "time is money".

What is the source of your first statement? According to SMB Bearings (A Guide to Bearing Retainers or Bearing Cages) "A full complement (or full ball) bearing contains extra balls and has no retainer. It is used for its greater radial load capacity although axial load capacity is very small due to the risk of the balls fouling the filling slot during rotation. These bearings can only be used at low speeds and bearing torque is increased due to ball to ball friction."

These are different than the cup-and-cone bearings used in bicycles. Of course, they are operating at low speeds, but bike bearings don't have "filling slots". In bicycle bearings with the sort of cages that are commonly used, it is possible to add at least one or two additional balls and *still* have enough space between the balls that there is minimal contact force. If this were a problem, then higher-end components would always use cages. This is not usually the case.

For example, my mountain bike (low-end Shimano hub) had 8 caged balls per side in the front wheel. My road bike (Ultegra hub) has 10 uncaged balls per side in its front hub. I replaced the caged balls in the mountain bike wheel with 10 balls per side. There is plenty of space, and when the balls contact each other they do so at a single point rather than all the places a cage touches each ball.

My old 10-speed had 7 (!) caged balls on each side of the bottom bracket. I replaced them with 11 balls per side, which represents a significant improvement in load-bearing capacity.

Finally, here's what Jobst Brandt had to say about cages (Source: Ball bearings (Jobst Brandt)):

"The bearings of which we speak in bicycles are primarily cup and cone
bearings in which the cage serves merely as a convenience for
assembly. It has no function other than that
. Cheap bearings, that
we needn't consider, often use cages to reduce the number of balls,
cages being cheaper than balls.

"The contact of one ball on another is not the reason for cages
although this is a problem with needle or roller bearings that have a
long contact line.
"

Steve
NASA would be one source I've read, among many others all of which indicate that ball retainers serve substantially greater purposes than convenience. What was Jobst's source (apart from his own rather expansive sense of authority)?

" . . . bearing torque is increased due to ball to ball friction." Loose ball friction is higher than in caged bearings due to skin friction between the balls. Skin friction is proportional to the square of the surface speed. Ball-to-ball surface speed is double ball-to-cage surface speed and thus skin friction is four times as high.

Last edited by AnkleWork; 03-29-18 at 09:05 PM.
AnkleWork is offline