Originally Posted by
Mike Mills
I do think this is true, however, I'm not sure about how valid it is if you have manufacturing defects. After all, there is a fatigue limit. The spindle surface is brittle. As few as one high stress cycle could cause a surface crack to propogate and invalidate the prior fatigue life history.
Yes, I'm wondering whether, had I had a close look at the spindle before it snapped, would I have seen a crack? And if so, how long before it failed would the the crack have appeared? Or would the crack have appeared just a few revolutions of the crack before it broke completely?
Originally Posted by
Mike Mills
Note, in Dawes-Man's bottom-most photo, there is a rather large "feature" which he has not yet polished out. In fact, the polishing has served to highlight it. It is on the right side of the shaft, almost dead center in the photo. Note also, there is a circumferential groove just slightly above that. In a brittle, case-hardened part, either or both of these could be a site at which a crack develops from fatigue.
I do like the idea of polishing the surface to minimize defects. This is the type of manufacturing processing that raises the price of the parts, so it wasn't done.
I like this idea too! It's a way you can easily add quality to components. I also like MikeX's suggestion of periodically dismantling pedals and inspecting the spindle surfaces.
On your observations of the marks on the lowest photo, the mark halfway up the spindle on the right looks to me like something has struck it as you would a tree you were felling, from above leaving an elongated triangle and ending with a slight ledge that you can just feel with a finger nail, about 0.2mm deep I'm wondering whether to polish it out but am worried about reducing the diameter of the spindle.
[IMG]
IMG_5330 by
Dawes-man, on Flickr[/IMG]
Originally Posted by
Mike Mills
Do we know if these spindles were machined or forged (or both)?
Looking closely at the spindle, pig-iron springs to mind. I remember my primary school teacher telling us how it was made with strands of iron bundled together. The spindle has strands running longways, which I first noticed from the slight pulsating feeling in my fingers holding the abrasive paper when I polished it. They are plainly visible in the following photo and they run the length:
[IMG]
IMG_5327 by
Dawes-man, on Flickr[/IMG]
Given what I have learnt in this thread about circumferential surface marks facilitating failure, it seems to me that these longitudinal strands serve to strengthen the spindle. Didn't work
