[TheForge] Re: Timken Case Hardening was File Making

[Andrew Vida]

That is an old lapidary technique.  It works very well.  Note the pipe 
should be soft material and lapping compound/fluid is introduced at the 
points of contact between them and the sphere.  When you get to a good 
shape, rinse the laps and sphere off and start again using the next 
finer grit.  Repeat until you have the surface you want.

This is not, however, the method used in grinding ball bearings.  As I 
recall, and this may be off in the details... actually I don't really 
have any details about it anymore, old age being what it seems, the raw 
bearings are poured onto a large flat lap (thousands of balls at a time) 
and another flat lap is placed on top with light pressure.  Compound is 
introduced and the top lap is moved over the balls.  IIRC the bottom lap 
is disk shaped with a lip like a cup to contain the rolling balls.  The 
upper lap is the same but without the lip and a bit smaller in diameter. 
  This allows the proper orbital motions to commence.  The balls are 
measured periodically and when the diameter is within tolerance, they 
are done.  I am sure this is all done with CNC control these days. 
Balls used to be tested using statistical samples.  These days, I would 
bet that every ball on the line is directly measured for diameter, 
spherical tolerance, and surface finish via laser examination.  The 
speed at which complete, complex, non-destructive, and 100% hands off 
measurement is carried out on high speed lines is really something to 
behold.  I got to see first hand at a few facilities in Berlin in 06.

Bruce Freeman wrote:
> I'm not sure what tolerance you can achieve, but spheres are routinely
> ground out of rocks using a clever apparatus.  Take two pieces of
> pipe, angle them up, maybe 120 deg. between them.  Leave a space for
> the rough sphere at the vertex.  So rough sphere is held by two pipes.
>  Now rotate the pipes, grinding material at ends of pipes.
> 
> In fact, the pipes point down, but that has to do with grit feed and
> waste, not with the general procedure.
> 
> Real marble marbles used to be made a different way.  Raceways in a
> pair of cast-iron wheels - CUBEs of marble placed in raceways
> (probably wet - not sure).  Rotate one wheel. Result: marble marbles.
> Marble is pretty soft.  Don't try this with agate.
> 
> Bruce
> NJ
> 
> On Thu, Mar 20, 2008 at 9:17 AM, Andrew Vida <osan at netlabs.net> wrote:
>>
>>  Mike Spencer wrote:
>>
>>  > Okayyy, so how do you -- er, they -- make spherical bearing balls?  I
>>  > recently had some enlightenment from the list about making flat things
>>  > using three pieces and a scraper.  So how you you make spherical
>>  > things to close tolerance?
>>
>>         There are high precision grinders that will get you 98% there.  I would
>>  imagine that the rest would  be lapping the pieces into each other.
>>
>>
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> 
> 
> 

-- 

	-Andy V.

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