Here is my 2c worth on preloading:
If you put a load on the end of a cantilever, it bends down. The top
surface is in tension and the bottom surface is in compression (somewhere
in the middle there is neutral axis with zero stress). Maybe our stubs with
bearings and spacers don't like to be in compression (noting that the
bearings and spacer are rotating, so go from tension into compression on
each revolution). So put some pre-load on the stubs, greater than the
compression load and the net effect is +ve load all round.
So, I know what to do with a cantilever.
Meanwhile I'll try not to think about this when I'm driving down the
highway!
---------------------- Forwarded by Alan Inglis/BC Research/CA on 11/02/98
09:02 AM ---------------------------
"David Ramsey" <dwramsey@worldnet.att.net> on 10/31/98 02:41:26 AM
Please respond to "David Ramsey" <dwramsey@worldnet.att.net>
To: "Matthew P Johnson" <spriteguy@juno.com>
cc: spridgets@Autox.Team.Net(bcc: Alan Inglis/BC
Research/CA)
Subject: Re: A question on wheel bearings
Yep, thats what I said:
> I was told by some racing vetrans that the stub shaft needs to be in
> tension to prevent breaking while cornering hard. I was instructed to
> put 40 to 50 ft-lbs on the castle nut while still maintaining a free
> spinning hub with no play.
> 0.025 to 0.030 inches thick (I was using Timken tapered roller bearings).
There is no proof that placing a axle in Tension will increase its
Shear strength, but I heard it from a guy that knew a guy who said after
breaking several axles he torqued them and never had a problem again.
If we use Poisson's ratio where nu= lateral strain/axial strain when
in tension the cross sectional area is reduced, which would decrease the
resistance to shear strains, so that the shear modulus of elasticity gives
G= E/2(1+v) where E= tension modulus and v = nu with the amounts tensil
load you are placing the axle in, it should not affect the shear strength
of the axle enough to weaken it much.
My brother in law knew a guy that worked for a guy that reduced the
toqure of his axle nut to 0 ft/lb and never broke another axle, so thats
good enough for me! The shear stress that my stock axle encountered when
landing after hitting the pot hole was about as great as I ever intend to
place them in so if they didn't break from that I'm happy.
I use timken roller bearings and no spacer, toqured to 10 ft/lb and
then backed off 1/4 to 1/2 turn to fit the cotter pin. I'm still waiting
for my axles to break.
Crash
|