The concept of using a spring for the pre-load has been around for some
time. The FWD Ford Escort diff carrier springs to mind, with a disc
spring for the pre-load on one side. Sometimes caused problems for
whatever reason when the spring went weak and the diff assembly shifted.
A mate had this and had to rebuild it. The normal thrust loads when
moving forwards were towards the fixed bearing. Use that generated high
thrust loads in the opposite direction, such as fast acceleration in
reverse or hard engine braking might compress the disc spring causing
problems we thought.
Another option used by Ford and others is threaded cups holding the
bearing outers, this is used in a number of Ford final drive units such
as the Sierra final drive for supporting the differential cage.
Surely the use of springs with taper rollers is to make sure that the
bearing is located correctly and stays in position, cars use taper rollers
in the front wheels ( rear wheel drive) but the bearings are not preloaded
if they were they would not last very long. Front wheel drive cars use
preloaded angular contact bearings because they can withstand greater
I have taper rollers on my minilathe, and as far as I can tell they are
primarily good for getting the shaft well centered, then for getting the
end float right. If you don't need both then taper rollers are a waste
of time, though they may also help vibration.
On my minilathe the taper rollers are compressed together by a nut on
the spindle, which I tighten until it isn't too tight.
The centering error and end float are then less than I can measure,
probably in the 0.5 micron range, and I can't see any serious bearing
Ymmv, but that's how I use them. No springs. Angular contacts may need
springs sometimes (depends on ball material) and load pretensioning, -
- but afaict not taper rollers, which just need to be accurately
spaced, rather than have an accurate load on them.
-- Peter F
Depends on the application .
In an automotive axle or steering hub ,such as in a 4wd then the
bearings are preloaded .
I have worked on large slurry pumps (10 / 8 ) 10" inlet 8" outlet used
in the mining industry ,the main shaft that carries the impeller has a
housing with large (4" ID ) opposed taper roller bearings usually set to
a clearance of 0.010" -0.012" .
"I'm not young enough to know everything."
There are many ways to pre-load bearings and a number of reasons for
doing so. Pre load is generally just to 'hold it all together' or in
other cases to ensure that the bearing remains in contact (ie the
bearing-ed part is correctly located) despite an applied axial load.
AC bearings must be pre loaded, TR's may be preloaded depending on the
eg Front wheel beaings on a (real) Beetle are adjusted with clearance
(010" rock at the wheel rim), the taper roller bearings on the front
of a Cortina are pre-loaded (guess those examples rather date me); in
each case the adjustment is made with a nut on the end of the shaft.
eg In a tool post grinder I have there are a pair of angular contact
bearings with a coil spring between them round the shaft.
The use of a spring in many applications is a convenience as it
adjusts the bearing 'reasonably well' without the need for any
adjustment - slap it together and forget it - great for quantity
production. A spring can be a coil spring round the shaft between the
bearings, it might be a 'Bellville washer' in the housing at one end,
it could be a wave spring in the housing (as in the Ford diff). In
some cases the preload can be effected by a use-once collapsible
component which crunches up under a given load thus loading that
particular shaft/bearing set to the correct load, but is not re-usable
since another bearing/shaft set will be a marginally different size.
As you suggest, shims can be used, but it is a tiresome way to do the
job as you need to dismantle the assemdly to make an adjsutment.
In some applications you might use a matched pair of TRs or ACs
located back to back and locked tight with a locking ring. The preload
is set by the manufacturer by sizing the relative positions of the
inner and outer. This is only really for high precision applications.
A brief comparison of the two types:
Taper roller bearings have a (much) larger load capacity, though a
slower maximum speed compared to angular contact bearings of the same
Taper roller bearings are significantly stiffer then angular contacts,
but have noticably higher friction/drag of the same size
Taper rollers are less able to accommodate angular mis-alignment than
angular contact bearings
Taper roller bearings are less accurate than an equivalent spec.
angular contact bearing. - This does not mean that all AC's are more
accurate than any TR
Try going to a bearing distributor or contacting a bearing
manufacturer direct and asking for their technical catalogue. It will
give you the full specs. for bearing types including end loads,
accuracies, clearances speed ratings etc. They used to be available
for free, but it wouldn't surprise me if they now charge as it is a
pretty solid tome, 700~800 pages. The same data is probably on-line,
but with SKF at least you need to register to get access.
An alternative used on motorcycle steering bearings is simply to have
a fine threaded nut & locknut to pre-load the bearings. The pre-load
is usually set by the torque on the adjuster nut, though I did once
see bearing drag being used as an indicator in one workshop manual.
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