The discussion below is about 85% correct, but has a major flaw.
If you look only at the section of axle covered by the bearings and spacer,
yes, that portion would be more resistant to bending loads than the axle
alone because of the increase in bending stiffness (moment of inertia) of
that cross section. A thicker beam is generally stiffer than a thinner
one. HOWEVER, the bending loads don't end here. They have to be
transmitted to the base of the axle, where it joins the spindle. This is
the critical area, where the maximum bending stresses are (that's why the
axle cracks here and not out at the tip). The bearings/spacer has no
effect on reducing the bending stresses here. Why? Because the inner
bearing is not physically, rigidly, integrally attached to the spindle
here. It just sits on it (ignoring the oil seal) , no matter how much
compression it is under. At the base of the axle, the bearing/spacer
combination has NO effect on the moment of inertia or stiffness of the
axle, or any capability to transmit or reduce the bending stresses here.
Steve Byers
Havelock, NC USA
'73 Midget GAN5UD126009G "OO NINE"
"It is better to remain silent, and be thought a fool
than to speak, and remove all doubt" -- Mark Twain
----------
> From: Mike Gigante <mikeg@vicnet.net.au>
> To: Lancer7676@aol.com; toobmany@bigpond.com
> Cc: spridgets@autox.team.net
> Subject: Re: Front Wheel Bearings... Explanation.
> Date: Monday, May 10, 1999 10:09 PM
>
> David,
>
> You can buy a crack testing kit from many rural supply places or
> from pegasus racing supplies.
>
> Back to the original question. It is simply a question of engineering
> mechanics. The spindle is a simple tapered solid beam. When the spacer
> is in there and correctly pre-loaded you have a composite beam with a
> much higher "Moment of Inertia". This simply means that for a given
> bending load there will be less deflection.
>
> The composite beam will also ensure that the local stresses on the
> surface of the spindle are much much lower than without the spacer.
> Why? Because the spacer is further out from the centreline axis of
> the assembly it contributes much more to the stiffness and takes the
> greater majority of the bending load (as tension/compression on
> the top/bottom half and vica versa) and thus reducing the maximum
> tension/compression stresses seen by the surface of the spindle.
>
> By reducing the maximum cyclic tensile/compression stresses on the
> spindle, the fatigue life is greatly increased.
>
> Note that it is the delta (max tension - max compression) that is related
> to the fatigue life. The fact that the spindle is pre-stressed in tension
is
> a very minor consideration as far as fatigue life is concerned.
>
> Mike
>
> -----Original Message-----
> From: Lancer7676@aol.com <Lancer7676@aol.com>
> To: toobmany@bigpond.com <toobmany@bigpond.com>
> Cc: spridgets@autox.team.net <spridgets@autox.team.net>
> Date: Monday, 10 May 1999 3:06
> Subject: Re: Front Wheel Bearings...
>
>
> >In a message dated 5/9/99 8:15:29 AM EST, toobmany@bigpond.com writes:
> >
> ><< For peace of mind I crack test the stubs >>
> >
> >Peter:
> >
> >How do you go about doing this? Is it something I can do in my home
garage
> or
> >is it a job for a machinist?
> >
> >--David
> >
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