Dan Burkhart said:Quoted message said:Quoted message said:Would this also qualify as old wives tales?
Quoted message said:Quoted message said:Yes, but the Barnett's assessment of the spindle transmitting its
load by friction is glaringly wrong as is their belief that with
lubricant the crank will go too far up the spindle. As is
explained in the FAQ cited, cranks continually move on the spindle
as pedal spindles do in the crank. The oxide layer in the square
bore of the crank is not a lubricant. Aluminum oxide is an
abrasive, but in this case (typically a shiny bore), the oxide has
no effect on the press fit.
Quoted message said:Quoted message said:So now let me ask you what you believe on this subject and why?
I've given you my perspective, with reasoning why this is so, and
means by which you can verify the matter while the ones you cite do
nothing of the kind.
Quoted message said:I came to this subject with preconceived notions to be sure, but not
a firm belief. I am open to being convinced of the error of those
notions. It occurs to me however, that there are two issues at play
here, one being crank retention, the other being transmission of
power. You seem to be focusing mostly on the latter.
I think the FAQ explains my position clearly. Crank retention is by
the retention bolt or nut. Without it, any (square taper) crank will
come off in use. I focused on power transmission in this round
because Barnett's make the glaring claim that friction transmits crank
force. If that were true we would have conical (round tapers) on the
crank spindle, these being stronger with lower concentrated stress for
an even greater press fit. As I said, fretting is apparent on steel
spindles from erosion by aluminum oxide of the crank bore.
Quoted message said:I base my acceptance of what I have been previously taught on the
fact that the purpose of lubrication, by it's very definition is the
reduction of friction between moving parts. Since the interface of
crank on spindle do not move in relation to each other, or at least
if they do, such motion should not be aided and encouraged by means
of lubrication, I find it reasonable that this mounting should by
dry, or treated with a locking compound such as Loctite.
That is a large part of the misunderstanding of this joint. It moves
and is a fretting interface. That is why it will separate without a
retaining bolt and why that bolt is looser after use than when
installed. Loctite in such an interface will have no effect, first
because it will be squeezed out of a useful film thickness on
installation, and secondly because the joint frets with stresses far
beyond what Loctite can withstand.
Quoted message said:Some here, however, with much more experience than I will have time
to accumulate over what remains of my life, seem to be lined up on
your side of this issue, so I will only say that for now, I continue
to mount em dry, but I will bear in mind what has been said here,
and try to make my own objective observations.
I don't find the difference significant although I an sure lubrication
reduces crank bore wear during installation while assuring repeatable
press. The main point of the discussion is the elasticity of
materials. A way to more easily look at this is to visualize all the
parts as being various stiffnesses of (hard) rubber. That way one can
visualize the distortions and motions that occur.
Jobst Brandt
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