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tradklime
Apr 30, 2005, 4:37 AM
Post #51 of 54
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Registered: Aug 2, 2002
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In reply to: ...whereas a flexible stem will load the edge with around 40% more than the downward load and so is more likely than a rigid stem cam to compromise the placement.
I'm curious about this statement, would you mind expanding upon it? Are you referring to the expansion force of the cam being near the lip of the crack, and therefor the load is being applied to the edge?
For what it's worth, I like the larger rigid stem units in uniform vertical cracks. I think they handle well in those circumstances. I generally dislike the smaller units because I find the stem too thick in relation to the size of the cams and that it interferes with placement in irregular cracks. But that's a whole other topic...
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rgold
May 1, 2005, 3:11 AM
Post #52 of 54
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Registered: Dec 3, 2002
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In reply to: In reply to: ...whereas a flexible stem will load the edge with around 40% more than the downward load and so is more likely than a rigid stem cam to compromise the placement. I'm curious about this statement, would you mind expanding upon it?
The whole point of a flexible stem is that it conveys the entire load even when bent. This means that, in a horizontal placement with the cable making an angle of about 90 degrees over the lower lip of the crack, a situation analogous to the pulley effect obtains. The load on either side of the contact point is the same and is equal to the applied downward load. The resultant force on the crack edge acts at about 45 degrees inward from the vertical and is about sqrt(2) X tension in the cable, which is about 40% higher than the downward load.
This means that if fracturing the lower edge of the crack is a concern, you're probably better off with a rigid stem.
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tradrenn
May 1, 2005, 11:51 PM
Post #53 of 54
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Registered: Jan 16, 2005
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In reply to: The picture of the broken flexable friend I scaned from an austrailian magazine with the accompanying article. I know that it is copywrited but in the interest of public saftry it is a good thing to discuss. I would post it if I knew how or email it to someone who could post it?
I also don't know how to put it into thread, but could you email it to me anyway please.
I have a set and I'm very interested in it.
Thanks a lot man
Tradrenn
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tradklime
May 2, 2005, 8:47 PM
Post #54 of 54
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Registered: Aug 2, 2002
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In reply to: The whole point of a flexible stem is that it conveys the entire load even when bent. This means that, in a horizontal placement with the cable making an angle of about 90 degrees over the lower lip of the crack, a situation analogous to the pulley effect obtains. The load on either side of the contact point is the same and is equal to the applied downward load. The resultant force on the crack edge acts at about 45 degrees inward from the vertical and is about sqrt(2) X tension in the cable, which is about 40% higher than the downward load.
The friction introduced by the cable over the edge will affect this somewhat. As well as the fact that the vector representing the force exerted on the edge of the crack (rigid with tie-off vs. flexible) will not act in the exact same direction makes it problematic to truely assess. And that a crumbling edge may cause more problems for the rigid stem. As always, it depends, but I now understand the potential advantages you explained.
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