MarkS
Moderator
I think you are comparing radii of two different things there (ie not equivalent measurements).
Simpson’s Pot - Anchors Rope wear
- Thread starter Ian P
- Start date
If a DMM anchor is manufactured from 8mm diameter wire it’s got a 4mm radius.
JasonC
Well-known member
All the discussion has been about wear, but how much wear is deemed too much? Based on complete ignorance, I guess a 13% reduction in radius means about a 25% reduction in diameter, and hence strength. This is certainly significant, but is it remotely dangerous?
What hasn't been mentioned, and isn't clear from the photos, is whether the wear patterns have left sharp edges, which would be much more concerning, I'd have thought.
What hasn't been mentioned, and isn't clear from the photos, is whether the wear patterns have left sharp edges, which would be much more concerning, I'd have thought.
JoshW
Well-known member
If the wear is equal across both ‘halves’ of the diameter then the reduction would still be 13%, if it’s less worn over the opposite ‘half’ then the reduction of the diameter would be lower than 13% (not double)
I think only Jason's terminology is wrong rather than his logic, if diameter / radius has reduced then cross sectional area will be worse as will strength.
98A looks like it has been fairly consistently threaded in the same direction by most users, whilst A92 has had ropes pulled through from both sides - presuming amount of use is about equal and pitches similar length, then it would seem that groove eventually cuts to approximate diameter of rope and damage by subsequent use may be minimised (A92 has average 6.8% each side compared to 7.3% on 98A). If A92 was on a slightly longer pitch (or where you can't see the bottom when setting up) then wear would be consistent with more rope being pulled through.
A single point may wear evenly both sides, depending on where you stand relative to the bolt when pulling down (so greater loss of cross sectional area), but a level pair of bolts will wear as shown by 98A (plus both a bit on the top), so varying reductions in diameter at each point, for same in radius. One of a pair, usually that furthest from the rigger, will likely also be worn by pulling the rope through whilst setting up (unless two are tied together to reach).
The metal around the bend of a bent to form bolt is going to be reduced anyway during production, unless it is initially thicker at that point, so you need to measure an unworn bolt to see what sort of percentage you actually started with (this is made more difficult as the bend may affect the reading, if the caliper jaws aren't sufficiently narrow). Would be worth measuring the two shown in appendix to see what difference the puller makes, as that will also deform diameter.
DMM eco anchors were apparently discontinued in 2005, after which the ICs were designed, as others available then weren't deemed to meet criteria. From CNCC "designing the IC resin anchor" document:
"There is an allowance for wear on the dimensions of the eye. It could be worn to half it's thickness and still be much stronger than an average karabiner. Before any wear the eye is immensely strong. Loaded in any direction it is about four times the strength of the average karabiner. The radius on each of the inside edges of the eye is 3mm which is much bigger than the minimum 0.2mm required by EN959 but this radius provides a smooth run for rope passed through the eye."
cncc.org.uk
My highlight. Note that this radius is the curvature of those edges in contact with the rope, not the total radius of the metal.
If both types measure as 8mm, then cross section of DMM is c.50 (π×r×r) and IC c.60mm2 (d×d), so 20% more metal.
98A looks like it has been fairly consistently threaded in the same direction by most users, whilst A92 has had ropes pulled through from both sides - presuming amount of use is about equal and pitches similar length, then it would seem that groove eventually cuts to approximate diameter of rope and damage by subsequent use may be minimised (A92 has average 6.8% each side compared to 7.3% on 98A). If A92 was on a slightly longer pitch (or where you can't see the bottom when setting up) then wear would be consistent with more rope being pulled through.
A single point may wear evenly both sides, depending on where you stand relative to the bolt when pulling down (so greater loss of cross sectional area), but a level pair of bolts will wear as shown by 98A (plus both a bit on the top), so varying reductions in diameter at each point, for same in radius. One of a pair, usually that furthest from the rigger, will likely also be worn by pulling the rope through whilst setting up (unless two are tied together to reach).
The metal around the bend of a bent to form bolt is going to be reduced anyway during production, unless it is initially thicker at that point, so you need to measure an unworn bolt to see what sort of percentage you actually started with (this is made more difficult as the bend may affect the reading, if the caliper jaws aren't sufficiently narrow). Would be worth measuring the two shown in appendix to see what difference the puller makes, as that will also deform diameter.
DMM eco anchors were apparently discontinued in 2005, after which the ICs were designed, as others available then weren't deemed to meet criteria. From CNCC "designing the IC resin anchor" document:
"There is an allowance for wear on the dimensions of the eye. It could be worn to half it's thickness and still be much stronger than an average karabiner. Before any wear the eye is immensely strong. Loaded in any direction it is about four times the strength of the average karabiner. The radius on each of the inside edges of the eye is 3mm which is much bigger than the minimum 0.2mm required by EN959 but this radius provides a smooth run for rope passed through the eye."
IC Resin Bonded Anchor
The IC Resin Anchor was conceived and designed by Simon Wilson BSc. with assistance from several friends exclusivly for CNCC and is now the only type of resin b
cncc.org.uk
If both types measure as 8mm, then cross section of DMM is c.50 (π×r×r) and IC c.60mm2 (d×d), so 20% more metal.
Taking 6.8mm diameter as worst affected part, area will be 36mm2 or 72% of original 50 (close to Jason's suggested 25% loss), although the actual area is more like an oval (π×r1×r2), so 42.7/50=85% metal remaining is probably a better representation [these are all approximations]
The good news is that the integrity of the bolts seems to be unaffected by 32 years in the rock and the wear is minimal over that period, so lack of gritty mud is a major advantage in most of Yorkshire.
A92 is presumably easier to thread from one side, but easier to pull down from other ...
The good news is that the integrity of the bolts seems to be unaffected by 32 years in the rock and the wear is minimal over that period, so lack of gritty mud is a major advantage in most of Yorkshire.
A92 is presumably easier to thread from one side, but easier to pull down from other ...
Last edited:
JasonC
Well-known member
Sorry, yes - I meant to type 'area' not 'diameter'
Did you find any of the worn edges were sharp?
This was the concern I had when reluctantly discarding an old Caving Supplies rack - not that the bars were 50% worn through, but that the scalloped sides of the worn area were developing a distinct edge.
Last edited:
Nothing was “sharp” as such more a “flattening”. Nothing noted concerned me about it cutting the rope.
It seems remarkable that we've got to a 10% loss of diameter without it raising an eyebrow. Good thing someone is keeping an eye out.
Interesting idea on the move to 9mm rope as an accelerant of wear, I think you could be right as although there is minimal mass the ratio of mass to contact surface is possibly more impactful? Difficult to get my maths around that, distortion under load greater with a 9mm but lower mass than an 11mm.
I wonder if you could use an inked up anchor and pull a rope through it to see the size of contact patch, treat as a bell curve and compare the contact patch to mass of ropes. That would give some garage science falsehood no doubt but sounds fun.
Interesting idea on the move to 9mm rope as an accelerant of wear, I think you could be right as although there is minimal mass the ratio of mass to contact surface is possibly more impactful? Difficult to get my maths around that, distortion under load greater with a 9mm but lower mass than an 11mm.
I wonder if you could use an inked up anchor and pull a rope through it to see the size of contact patch, treat as a bell curve and compare the contact patch to mass of ropes. That would give some garage science falsehood no doubt but sounds fun.
I expect that lots of people have noted the wear as nothing to worry about (the loss is only in one dimension, not both, so actually less than original figures suggest). As long as sharp edges don't form then you will get a point where the abrasion switches to the upper surface as the minimum bend on rope will no longer put as much pressure on the sides.
Unfortunately I think the movement inherent in dragging a 9mm rope over the inky metal will obscure the difference to an 11mm
Unfortunately I think the movement inherent in dragging a 9mm rope over the inky metal will obscure the difference to an 11mm
Last edited:
zzzzzzed
Active member
I know plenty of people who have been using 9mm ropes in there since the 1980s. Usually discarded 9mm climbing ropes.
I remember two climbers who used to drive up to the Dales every Wednesday evening to do Simpsons pull through as part of their training for the Walker Spur. I don't think they did the Walker but it got them fitter.
JAA
Active member
Off topic but I was suprised how much wear I hadn’t particularly noticed on a traverse line mallion which isn’t subject to the same style of rope rub as an anchor used for pull through trips, more a “jiggling” motion so to speak I expect! Although that’s likely had 30 years to wear away.
Maillons are usually subject to electrolysis rather than wear.
And on a previous question, yes they do come twisted:
And on a previous question, yes they do come twisted:
@Ian P and @s_allshorn - thank you for doing this
it is great to see some information about the wear. i was wrong before to assume that wear can be neglected as a factor.
it would be interesting to find out
many people will have have passed the anchors as they approached this condition. presumably most did a pre-use inspection and were happy to continue, judging that the anchors are still amply good enough, and that anyway there are two or more. maybe they didn't like what they say but were committed to a through trip and had no choice. how many people have reported excessive anchor wear to the CNCC? (in other words, is anchor wear an issue that concerns the community)
last thought - are people checking P-hangers according to the instructions. (i see riggers not doing this) is this a good basis to add more links in the chain for people to inspect? and single-point-of-failure links where one was not before?
it is great to see some information about the wear. i was wrong before to assume that wear can be neglected as a factor.
it would be interesting to find out
- what the slit pot anchors are like (and the other routes)
- how strong the worn eyes are (e.g. have some DMM anchors tested after removal?)
- an estimate of the sectional loss of metal, and an analysis of what proportion that loss would be on a IC anchor
- how long we anticipate it would take to wear an IC anchor
- what proportion of bolts installed are as a result of wear (i.e. as a fraction of the 1000s installed in dales caves)
- whether the new/alternative bolt orientation improves the wear pattern
many people will have have passed the anchors as they approached this condition. presumably most did a pre-use inspection and were happy to continue, judging that the anchors are still amply good enough, and that anyway there are two or more. maybe they didn't like what they say but were committed to a through trip and had no choice. how many people have reported excessive anchor wear to the CNCC? (in other words, is anchor wear an issue that concerns the community)
last thought - are people checking P-hangers according to the instructions. (i see riggers not doing this) is this a good basis to add more links in the chain for people to inspect? and single-point-of-failure links where one was not before?
Chocolate fireguard
Active member
Anyone who has hacksawed through a hefty round bar knows it's easy to cut the first few mm but thereafter towards the middle every mm takes longer.
The same thing must be happening here.
If these anchors are ok until half the metal has gone, as has been suggested (sensibly in my opinion) they are probably good for another 50 years.
The same thing must be happening here.
If these anchors are ok until half the metal has gone, as has been suggested (sensibly in my opinion) they are probably good for another 50 years.
JoshW
Well-known member
‘Industry’ standard is 10% or 1mm whichever happens first for wear on metal. I cannot see how anyone would justify setting precedent of waiting for 50% - that would be crazy!
And before anyone jumps at me - I know we are not professional/commercial/industry, and are caving recreationally, but, 50%.. come on
Mark Wright
Well-known member
I think our insurers might have something to say about officially deviating from the industry best practice of 10% or 1mm maximum allowable wear.
A club trip leader may be treated as if they were acting in a professional capacity if there was a serious accident. Unfortunately, this would probably only be decided in a court room, and it's always best to avoid those.
Cavematt
Well-known member
As lovely as it would be to know all of these things before making any decisions regarding the chains, I'm not sure this is realistic.
The CNCC is currently lacking interest for one of it's most important roles to function at the moment (Treasurer), and so far, only verbal interest in two of our other roles (Chair and Access Officer), all of which are becoming vacant in March. To gather the information and perform the analysis you are suggesting here is a substantial research project likely to involve months or years of effort.
I'm not going to suggest there is nobody willing to take this on... but I'm not convinced.
Even if we did have a volunteer, gathering this data before installing chains in Simpson Pot (and then the numerous ensuing discussions) is going to take lots of time. The volunteer offering to install these chains may have simply lost interest by then!
This discussion reminds me of my brief time as BCA Secretary... I was so infuriated that the organisation was never doing anything because everything got filibustered by excessive discussion, committees and sub-committees... decisions would get spread out over so many meetings, and so much nice-to-know additional information would get requested by so many people, that volunteers just lost interest and it was easier just to do nothing.
There is a balance to be struck between due diligence to make the correct decisions, and actually delivering for northern cavers in a way that reflects the volunteer nature of the organisation and that it is meant to be fun.
Generally I feel CNCC strikes the right balance here, but I'm hardly able to give an unbiased opinion on that
I can confirm that in all my time of monitoring the CNCC's report submissions, I have not seen any reports of anchor wear as a result of pull-through. Presumably this has always gone unnoticed by the hundreds of cavers who must pass through these pots each year.
Taking actions to mitigate future anchor damage on the most vulnerable sites (i.e. by installing the chains/ring, or similar on our longest and most popular pull-through pitches) seems like a much more practical here-and-now solution than waiting to ascertain how much wear is too much, and then having to continuously monitor this over several years, before taking any action.
That's not to say we shouldn't then gather more data on anchor wear from the remaining shorter pull-through pitches (and also wear on the pull-through rings if they are installed), if a volunteer is willing to take that job on as a longer term project.
Ps; I am speaking from my own personal opinion, and not in any CNCC capacity.
