On Sat, 3 Dec 2005 22:44:51 -0500, "Terry Keeley" tkee(no
spam)@(or mail)rogers.com wrote:

Ive not removed bearings from your particular mill..but based on most
angular contact bearings...they should be mounted like this " "

With a hand snug preload.


Are you sure that's right? That symbology is for "face to face" mounting
and everyone I've talked to have said "back to back" is the way to go.


Lots of recommendations on which way to mount the bearings but no
input on why!

As I see it, if the angular contact bearings are the only
bearings on the shaft they should fit because that gives
radial location, end thrust location and maximum resistance to
angular misalignment of the shaft. By angular misalignment I mean
the axis of the shaft shifting so that the shaft centre line
traces out a double cone with the vertices located between the
two bearings. An appropriate case for this pairing arrangement
would be automobile front wheel bearings.

If,as is common, on a Mill or a Lathe a third bearing is fitted
well separated from the angular contact pair it is THIS bearing
that provides the primary resistance to shaft angular movement.
Any residual difference between this and the shaft angle defined
by the angular contact pair results in the shaft being over
constrained and generates large interbearing forces. This means
that the angular contact bearings shoud be mounted to minimise
the angular constraint - one way of visualising this is to
realise that this is half way to the geometry of a self aligning
bearing.

I am not a bearing expert but I think this is a reasonable way of
looking at it.

Jim