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Simpson’s Pot - Anchors Rope wear

Chocolate fireguard

Active member
Does wear make sharper edges that could cut or chafe a rope (especially on a pull through) Id imagine this would cause a problem sooner than the metal failing
Aside from whether a 50% loss of strength in an 8mm anchor causes a dangerous situation (answer, no) that’s also a valid question.

The first place to start would be an anchor that has supposedly been eroded from an “O” profile to a “D” profile due to pulldown, with the flat side horizontal, like in the first drawing. I think that’s how many people would initially imagine the situation.

The other anchor is some distance off to the right.

T1 is the tension in the vertical rope and T2 that in the horizontal one.

T is the resultant force applied by the rope to the anchor and so the force on the rope will be in the opposite direction. It will certainly risk damaging the rope.

But on pulldown the rope will tend to blunt that sharp edge.

So the obvious question is “how can that edge have developed due to pulldown in the first place?”.

And I think the obvious answer is “it can’t”.

If that setup continued in use then the hatched area on the left would be removed by successive ropes.

Applying that same argument to the RHS of the “D” and remembering that the downwards force there is minimal because of the other anchor off to the right, then starting with an unworn anchor I think the profile after about 50% of the metal has gone will be as in the second diagram.

There will be minor differences on that RHS if the other anchor is a little below or above, but nothing really on the load side. The rope would not be running over any sharp edges.

Apologies for the poor drawings.
anchor.jpg
 

mikem

Well-known member
The physics is right, but wear isn't really seen on the top surface of the circumference, as the curvature of metal is much smaller than the possible bend in the rope - it occurs mostly on the outside of top "corner" of the circle, and the upper part of bolt may be worn in a different position along the eye, depending on relative position of other anchor. (More like if you rotate the 2nd picture c.30 degrees anticlockwise). The sharpest edges will be along the sides of the groove once it's well cut in, but even these won't be sharp enough to affect the rope - see photos on original post.
 
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Bob Mehew

Well-known member
The first place to start would be an anchor that has supposedly been eroded from an “O” profile to a “D” profile due to pulldown, with the flat side horizontal, like in the first drawing. I think that’s how many people would initially imagine the situation.
I think a better place to start is with a rope on a 'new' anchor. I suggest you need to include the impact of friction in your consideration of forces, which will 'take out' some of the tension in the rope as it curves around the anchor. So I am predicting the wear will be mostly on the outer edge as mikem stated, less so on the 'top' edge and even less on the other anchor's 'top' edge and possibly a bit more on the other anchor's vertical edge. That is due to the weight of the dangling rope causing a lesser degree of friction which will be less than the equivalent force pulling the rope down. You could simulate it with a loop of sanding paper (made from a belt sander) placed around two pulleys, one driven and two rods. That should demonstrate the theory within a minute or two.
 

Chocolate fireguard

Active member
I think a better place to start is with a rope on a 'new' anchor.
You seem not to have realised that the first step was to show that any sharp edge would be removed - so can never have been created in the first place.
I suggest you need to include the impact of friction in your consideration of forces, which will 'take out' some of the tension in the rope as it curves around the anchor.
So perhaps the tension in the horizontal rope T2 should have been represented by a shorter arrow than T1 and the resultant T by an arrow closer to the vertical than to 45 degrees? You might want to look at the top diagram again.
Sometimes it's better just to get things right with no explanation, so that those "in the know" will understand without the need to bore the others with stuff that doesn't matter.
So I am predicting the wear will be mostly on the outer edge as mikem stated, less so on the 'top' edge
A bit like my lower diagram then?
and even less on the other anchor's 'top' edge and possibly a bit more on the other anchor's vertical edge.
If the anchors are at the same level and the pulldown is always at the same side. Otherwise anything can happen - except sharp edges of course.
That is due to the weight of the dangling rope causing a lesser degree of friction which will be less than the equivalent force pulling the rope down. You could simulate it with a loop of sanding paper (made from a belt sander) placed around two pulleys, one driven and two rods. That should demonstrate the theory within a minute or two.
Yes.
 

JAA

Active member
Hi Jaa, you seem to be upset, sorry about that. I do disagree with you and it's fine. I would just like to check, how do you know the chains are going on existing anchors?

Perhaps a query for the other thread as this is about the wear discovered on the anchors rather than the proposal to use a fixed aid
If you read Ian P’s proposal then it actually includes removal of some anchors to rationalise the situation on at least one of the pitch heads. And while I don’t know the pitch head well enough to be certain I suspect it will end up with less anchors not more!
I do have every confidence that Ian proposes to do the work in as sensitive and “eco friendly” way as possible. Our opinions obviously differ on what counts as too many anchors or unnecessary anchoring which is fine, no problem at all with people having opposing views.
 

Mark Wright

Well-known member
Rather than trying to predict how a pull-through anchor will wear with your T's, T1's, T2's and bits of sandpaper, why not just install one on a cliff face somewhere and keep pulling 40m of wet, dirty 8mm, 9mm, 10mm and 11mm rope backwards and forwards through it and see what actually happens?

I would have thought the manufacturers of these pull-through systems would have already tested it but probably only with dry, clean dynamic rope.
 

Chocolate fireguard

Active member
Rather than trying to predict how a pull-through anchor will wear with your T's, T1's, T2's and bits of sandpaper, why not just install one on a cliff face somewhere and keep pulling 40m of wet, dirty 8mm, 9mm, 10mm and 11mm rope backwards and forwards through it and see what actually happens?

I would have thought the manufacturers of these pull-through systems would have already tested it but probably only with dry, clean dynamic rope.
I'm happy that I know how it will wear, assuming the 2 anchors are more or less on the same level.
The rate at which it will wear will depend on so many things that it is unknowable.
 

Bob Mehew

Well-known member
You seem not to have realised that the first step was to show that any sharp edge would be removed - so can never have been created in the first place.
Oh. I accept that the area of wear of the anchor will mostly depend upon the resultant force from the forces in the two ropes and to a lesser extent the degree of friction. I suggest that the location of that area of wear will depend upon the 'angle' of each rope as it is fed into or pulled out of the anchor, each being within a cone whose apex is at the area of wear. For a two anchor system, the rope coming from the second anchor will have a very small cone whilst the cone of the pull from the caver beneath will be somewhat larger though still restricted by the nature of the pitch. I find it difficult to visualise a situation where the cones can be sufficiently large so as to stop the build up of a sharp edge parallel to the side of the rope. That is why Bob Dearman's solution of using a large ring connected by chain or wire strops avoids the localised wear in a fixed anchor by allowing the area of wear to change around the ring.
 

Ian Ball

Well-known member
If you read Ian P’s proposal then it actually includes removal of some anchors to rationalise the situation on at least one of the pitch heads. And while I don’t know the pitch head well enough to be certain I suspect it will end up with less anchors not more!
I do have every confidence that Ian proposes to do the work in as sensitive and “eco friendly” way as possible. Our opinions obviously differ on what counts as too many anchors or unnecessary anchoring which is fine, no problem at all with people having opposing views.

I should say firstly that the discovery of worn anchors that require removal has made a lot of the discussion moot because the IC anchor is a marvellous step forward, I take my hat off Mr Wilson et al.

In respect to the pitches where chains were proposed the problem with Ian Patrick's posts are that they contract each other.
Edit: I see an additional meeting item has been added to the meetings page on the cncc website. A much more in depth document which is good, I must say. I believe it may be the basis of a post on the other thread.

Original Proposal - https://cncc.org.uk/file/98b26f5e-92ab-a42c-9435-f57eef556113
"the infamous Slit Pot and Swinsto Great Aven, the former being notorious for stuck ropes (and some stuck cavers).
Ian has advised that the optimum solution for both pitches would require the anchors to be
linked with chains to a master point, and he has installed anchors in anticipation of this."

[not a direct quote but not incorrect, and author uncredited]

So anchors have been installed at Slit Pot and Swinsto Great Aven

Additional meeting item - https://cncc.org.uk/file/d2bd086b-fefd-c710-6bba-739e0fdfb136
"Linking two of the existing anchors here with a chain would provide a single attachment point and allow a clean up of the surplus anchors."

So new anchors haven't been installed here? and the linking of two existing anchors will allow the removal of surplus anchors too?!! Superb!
(Dare I suggest that the 'surplus' anchors are the ones Ian just installed in anticipation of Slit Pot chain? I do dare! ha)

I am reminded that the discussion at the CNCC meeting is if we want to take on the ownership of fixed aids.
I have just spent a moment looking at the worn anchor document at the start of this thread, very good indeed.

Ok, enough from me.
 

Chocolate fireguard

Active member
Oh. I accept that the area of wear of the anchor will mostly depend upon the resultant force from the forces in the two ropes and to a lesser extent the degree of friction. I suggest that the location of that area of wear will depend upon the 'angle' of each rope as it is fed into or pulled out of the anchor, each being within a cone whose apex is at the area of wear. For a two anchor system, the rope coming from the second anchor will have a very small cone whilst the cone of the pull from the caver beneath will be somewhat larger though still restricted by the nature of the pitch. I find it difficult to visualise a situation where the cones can be sufficiently large so as to stop the build up of a sharp edge parallel to the side of the rope. That is why Bob Dearman's solution of using a large ring connected by chain or wire strops avoids the localised wear in a fixed anchor by allowing the area of wear to change around the ring.
I think I understand what you mean by a sharp edge parallel to the side of the rope.
But a 10mm rope will not cut a 10mm wide parallel-sided slot. The top will be wider as the first few thousand(s?) of ropes chose different paths. Behaviour pretty well described by your use of "cones" except that initially the top of the cone is truncated (conical frustum?). This is seen on the photos in the OP.
The basic idea still is that no edge capable of increasing the pressure on a part of the rope will be allowed to develop.
 

IanWalker

Active member
Would a closer inspection, measurement, and maybe testing of the worn anchors provide sufficient useful information?

A sound understanding of the theory has its uses, but simulating how they might wear in theory seems to be less useful than looking at the ones that have already worn.

Cheers
 

mikem

Well-known member
I posted link to new document on other thread yesterday as we are in danger of discussing the Same things on parallel posts!
 
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