"Wild_Bill" wrote in message
...
I didn't mean to suggest that ball bearings were individually hand selected
from batches of bearings to achieve the correct fit.

A more-common all metric dimension bearing would likely be cheaper than a
metric bearing with an inch I.D. in most cases.
If the manufacturer had size and strength constraints a less common
bearing may be more suitable.

When machine manufacturers are designing their parts that the bearings
will mount/mate to, they will typically machine their shaft and housing
dimensions to match a commonly available bearing.

When GLU (guys like us or maintenance/repair folks) are working
with/repairing existing machines, the bearing mating parts are first
measured, then an appropriate, commonly available (with any luck) bearing
is ordered/selected to fit the application.

As you can see by the other responses, the buffing arbor shaft was
machined for several reasons. Positioning the shaft's length relative to
the arbor's housing primarily, and to fit the bearings' I.D.s, and to use
common mounting hardware.. 1/2" nuts.
The shaft remains stronger in the center (providing shoulders for the
bearings), utilizing a commonly available pulley I.D., held in place
laterally, and commonly available mounting hardware for the mounted
accessories.

If the shaft were just 1/2" diameter, shaft collars or some similar
hardware that wouldn't compromise the shaft strength would be required to
lock or locate the shaft in place (more hardware generally means higher
manufacturing cost), and the bearings would've been more expensive.

The arbor manufacturer had a responsibility to market a fairly safe
product, one that wouldn't fly apart, safe enough for a DIY-type to take
home and use.

There are ball bearings that have integral locking features for securing
the inner races to shafts, but they are more expensive than an ordinary
ball bearing assembly.

The machining that was performed on the arbor shaft wasn't an expensive
operation, performed on automated machines it was probably completed in
probably less than a minute from raw barstock to a finished, threaded
part.

Who knew that such a simple piece of equipment would provide so many lessons
in engineering and associated history and economics? Thanks everybody for
such a detailed explanation. Some of the links provided are useful as
reference. Again, my Google technique has proved deficient as I have been
looking for them or something similar without success for the last two
weeks.

In the final analysis the whole thing cost me $5 and most of the procedures
suggested seem to involve greater costs than I can justify at present. I
shall just keep looking at it 'cos it's pretty and an idea for good use will
come to me in time :-)

--
Michael Koblic,
Campbell River, BC