|
ridgeclimber
Apr 3, 2006, 11:46 PM
Post #1 of 36
(1971 views)
Shortcut
Registered: Sep 16, 2005
Posts: 163
|
Alright, this is intended to be a branch-off of my previous discussion on the breaking strength of cams. Here we will discuss at what strength a cam could be expected to rip (not break, rip) under normal circumstances.
Here's the situation: good sized cam, could crack, good general placement. Very hard fall. At what strength (in kN) could the cam be expected to rip? It would depend, is the first answer, but I bet we could come up with a number.
Could this cam be expected to fail at all under normal circumstances? There's always the bad luck factor, but excluding that, how far can we trust this cam?
I've placed enough crappy gear to know that most placements aren't ideal. But we're speaking hypothetically.
Can a normal (but hard) fall rip this cam?
|
|
|
|
|
styndall
Apr 4, 2006, 12:03 AM
Post #2 of 36
(1971 views)
Shortcut
Registered: May 29, 2002
Posts: 2741
|
I am under the (possibly incorrect) impression that a cam well-placed in good rock would break before pulling. I've not experienced it personally, but I've read here of people falling on black aliens, which, though deforming terribly, held the falls.
|
|
|
|
|
billcoe_
Apr 4, 2006, 12:15 AM
Post #3 of 36
(1971 views)
Shortcut
Registered: Jun 30, 2002
Posts: 4694
|
I was surprised to see Malcom Daly say that they had tested a bunch of #1 Maxcams AND SOME OTHER BRANDS OF CAMS and was surprised to see failures as low as 6KN, even of other brands wherin the breaking strength was a rated 14Kn.
He didn't break that down, but it sure is a curious thing. Anyone else have any independent test data.
|
|
|
|
|
ridgeclimber
Apr 4, 2006, 12:32 AM
Post #4 of 36
(1971 views)
Shortcut
Registered: Sep 16, 2005
Posts: 163
|
Scary. 6 kN is not very high. Anyone have any more data?
|
|
|
|
|
patto
Apr 4, 2006, 12:46 AM
Post #5 of 36
(1971 views)
Shortcut
Registered: Nov 15, 2005
Posts: 1453
|
In reply to: I am under the (possibly incorrect) impression that a cam well-placed in good rock would break before pulling. I've not experienced it personally, but I've read here of people falling on black aliens, which, though deforming terribly, held the falls.
That is true. The harder the cam is pulled then the even harder it grips. A well place cam should either break or break the rock around it before it fails.
|
|
|
|
|
ridgeclimber
Apr 4, 2006, 11:19 PM
Post #6 of 36
(1971 views)
Shortcut
Registered: Sep 16, 2005
Posts: 163
|
billcoe, when you say "failure," do you mean breaking or merely blowing the placement? If it's breaking strength, that is consistent with what patto has said. On the other hand, if we have cams actually BREAKING at 6KN that's a major f-ing problem.
I think that under normal circumstances, it would be very difficult to achieve the 14 or 15 kN necessary to break a cam even with a FF2. But if they break much lower than that.... :shock:
|
|
|
|
|
phunkdified
Apr 4, 2006, 11:42 PM
Post #7 of 36
(1971 views)
Shortcut
Registered: Feb 22, 2005
Posts: 14
|
(pushes his glasses up onto his nose)
actually the myth that the harder a cam is pulled the harder it grips is incorrect.
the whole concept of the cam is based on an optimum friction angle which is why the cam has that nice organic flared shape, it is based on natural shapes like shells that grow at a constant angle.
the guy that created the first camming device (Jardine?? i think) was a smart dude he figured that the optimum angle for maximum friction was somewhere between 11 and 14 degrees so he set the constant angle of the camming device to a range of these "friends" and then tested them to find out what the best angle is this is why smooth cams hold better or at least as well as grooved cams, smooth ones have more surface area in contact with the rock, therefore more friction......
anyway if there is a discrepancy between the empirical test strength and the actual breaking strength of cams in the real world, i would bet that the variables that are inherent within climbing would be the main culprit. the tested strength of the units are based on specifically set up parameters.
since gear placement is based on the perceived direction of pull in the event of a fall there are bound to be some disparity between the two numbers, also the amount of fatigue in the material or small imperfections due to wear and tear........i dunno but for my own piece of mind I'm going to rationalize the hell out of this.....either that or throw out all my gear and take up golf........ :lol:
|
|
|
|
|
ridgeclimber
Apr 4, 2006, 11:46 PM
Post #8 of 36
(1971 views)
Shortcut
Registered: Sep 16, 2005
Posts: 163
|
That's the spirit! :lol:
However I found your point a little confusing. You first said that the idea of breaking always preceding ripping was wrong, but you seemed to support that view. Can you elaborate?
|
|
|
|
|
phunkdified
Apr 5, 2006, 12:31 AM
Post #9 of 36
(1971 views)
Shortcut
Registered: Feb 22, 2005
Posts: 14
|
perhaps it was a bit confusing, what i was saying i disagreed with.........
was that the harder a cam is pulled on the harder it grips......this statement is incorrect since the "holding" capacity of a cam is based on the amount of friction it generates, a bit unnerving to be sure, if you can get a hold of the wild country "CAM book" it goes through a good explanation.
i would expect that cams would fail(break) everytime (if you generated enough force to exceed the upper limits which they rate them with)......IF (and this is a big'un) we could place a cam PERFECTLY everytime, with no possibility of pull-out due to rope drag walking the cam around and changing the direction of the protection or if there were no imperfections or weaknesses associated with the crystal structure of the rock......again variables abound......
its what makes climbing exciting, the variability
hmmmmmmmm......upon reading this post over, i think i need to take a break from writing about technical stuff on here and reread my degree project paper, if it is as unclear as this post i'm in trouble....... :shock:
|
|
|
|
|
tradrenn
Apr 5, 2006, 2:01 AM
Post #10 of 36
(1971 views)
Shortcut
Registered: Jan 16, 2005
Posts: 2990
|
There is one thing that gets my head spinning in climbing.
Fall Factor vs. Kilo Newtons (KN)
Let me explain
The fall on gear is rated in FF ( fall factor )
The strength of gear is rated in KN ( Kilo Newtons )
What is up with that, I'm I missing something ?
How many KN's is FF 1 ?
How many KN's is FF 2 ?
|
|
|
|
|
ridgeclimber
Apr 5, 2006, 2:08 AM
Post #11 of 36
(1971 views)
Shortcut
Registered: Sep 16, 2005
Posts: 163
|
Thanks for the clarification phunk.
Tradrenn: depends on the rop. Max fall force that can be generated on the climber by dynamic ropes tested by the UIAA is 2642 lbs or something like that. Fall factor means the length of the fall divided by the amount of rope out. It's a measure of how hard a fall is, taking into account force absorption by the rope. Thus in theory, falling four feet with two feet of rope payed out will yield the same force as falling 400ft with 200ft payed out. Notice the "in theory;" very important phrase. :wink:
|
|
|
|
|
styndall
Apr 5, 2006, 2:26 AM
Post #12 of 36
(1971 views)
Shortcut
Registered: May 29, 2002
Posts: 2741
|
In reply to: There is one thing that gets my head spinning in climbing. Fall Factor vs. Kilo Newtons (KN) Let me explain The fall on gear is rated in FF ( fall factor ) The strength of gear is rated in KN ( Kilo Newtons ) What is up with that, I'm I missing something ? How many KN's is FF 1 ? How many KN's is FF 2 ?
You can't take the fall factor, run it through some algebraic process, and end up with the kNs felt by the top piece or the belayer. The fall factor is simply the ratio of the distance fallen to the amount of rope that absorbs the fall. The force is related to the fall factor, the elasticity of the rope, the weight of the climber, the weight of the belayer, the amount and rate of slippage of rope through the belay device, and other things. It's prohibitively complicated to calculate, so the only way to get a number is to attach dynamometers or scales at key points in a system and fall on it.
This doesn't happen in the real world.
The thing you're missing is that the fall on gear is not measured in terms of fall factor, but in terms of kilonewtons, like other forces. Fall factor just gives a rough idea of how much force the rope will absorb in the process of stretching.
|
|
|
|
|
curt
Apr 5, 2006, 2:29 AM
Post #13 of 36
(1971 views)
Shortcut
Registered: Aug 27, 2002
Posts: 18275
|
In reply to: There is one thing that gets my head spinning in climbing. Fall Factor vs. Kilo Newtons (KN) Let me explain The fall on gear is rated in FF ( fall factor ) The strength of gear is rated in KN ( Kilo Newtons ) What is up with that, I'm I missing something ? How many KN's is FF 1 ? How many KN's is FF 2 ?
OMFG :lol: :lol: :lol: :lol: :lol:
Curt
|
|
|
|
|
curt
Apr 5, 2006, 2:43 AM
Post #14 of 36
(1971 views)
Shortcut
Registered: Aug 27, 2002
Posts: 18275
|
In reply to: The fall factor merely allows you to remove the length of the fall from the peak impact force equation.
Curt
copied from a post I made in a similar thread in March, 2005.
|
|
|
|
|
brent_e
Apr 5, 2006, 3:02 AM
Post #15 of 36
(1971 views)
Shortcut
Registered: Dec 15, 2004
Posts: 5111
|
In reply to: I was surprised to see Malcom Daly say that they had tested a bunch of #1 Maxcams AND SOME OTHER BRANDS OF CAMS and was surprised to see failures as low as 6KN, even of other brands wherin the breaking strength was a rated 14Kn. He didn't break that down, but it sure is a curious thing. Anyone else have any independent test data.
If I remember correctly, the other cams failed when pulled off axis. They are rated for a certain strength when the cam is pulled with the stem perfectly perpendicular to a line connecting the points of contact of the lobes on the rock, and they were failing when the former parameter was not met.
kinda spooky! how many placements of yours are perfect like that?! :D
good thread!
Brent
|
|
|
|
|
curt
Apr 5, 2006, 3:24 AM
Post #16 of 36
(1971 views)
Shortcut
Registered: Aug 27, 2002
Posts: 18275
|
In reply to: In reply to: I was surprised to see Malcom Daly say that they had tested a bunch of #1 Maxcams AND SOME OTHER BRANDS OF CAMS and was surprised to see failures as low as 6KN, even of other brands wherin the breaking strength was a rated 14Kn. He didn't break that down, but it sure is a curious thing. Anyone else have any independent test data. If I remember correctly, the other cams failed when pulled off axis. They are rated for a certain strength when the cam is pulled with the stem perfectly perpendicular to a line connecting the points of contact of the lobes on the rock, and they were failing when the former parameter was not met. kinda spooky! how many placements of yours are perfect like that?! :D good thread! Brent
Further more, as you know, there is a trade-off between a cam's holding power and its range, that is determined by the cam angle. And, if you place any given cam in a flared crack, you effectively decrease its cam angle and increase the forces applied to the lobes and axle(s) of the cam. Just one other thing to keep in mind.
Curt
|
|
|
|
|
patto
Apr 5, 2006, 3:36 AM
Post #17 of 36
(1971 views)
Shortcut
Registered: Nov 15, 2005
Posts: 1453
|
In reply to: (pushes his glasses up onto his nose) actually the myth that the harder a cam is pulled the harder it grips is incorrect.
the harder a cam is pulled on the harder it grips......this statement is incorrect since the "holding" capacity of a cam is based on the amount of friction it generates,
It is not a myth it is basic physics.
Even without calculating it, common sense would tell you that a cam increases its grip with load. If i didn't it would come out!! By the way, the word grip refers to the forces applied to the surface NOT the friction. But since friction increases linearly with grip the 'holding' strength likewise increase. But lets forget the semantics and look at the numbers.
Based on the WC cam angle of 13.75 we can work out the grip strength. (ignoring the spring tension which is negligable once proper load is applied)
Load Expansion pressure on rock (spread over all cams)
0kN 0kN
0.1kN 0.409kN
1kN 4.09kN
10kN 40.9kN
Hmmm, seems to be increasing the grip to me.
In reply to: smooth ones have more surface area in contact with the rock, therefore more friction......
Not really true.
More surface area does not always mean more friction as a larger surface area spreads the presure out. The standard model of friction increases linearly with presure and area and so friction is NOT dependent on surface area. Rock/metal contact very closely follows the standard friction model. In reality, larger surface area cams can cause lower friction due to the presence of sand. (I would be more careful with FAT cams around sand) For a similar reason, fat slick tires can be terrible in the wet.
|
|
|
|
|
tradrenn
Apr 5, 2006, 4:18 AM
Post #18 of 36
(1971 views)
Shortcut
Registered: Jan 16, 2005
Posts: 2990
|
Ridgeclimber, Styndall, Curt
I just want to explain that when I think of FF I also think of Newton Law ( #3 , if I'm not mistaken )
The falling body doubles its waight for every meter of a fall, up to 173 times ( not exactly about that number ) so at the end of the fall a climber's body will waight ??? of kg. ( or pounds ), yet we still use a FF.
|
|
|
|
|
styndall
Apr 5, 2006, 4:52 AM
Post #19 of 36
(1971 views)
Shortcut
Registered: May 29, 2002
Posts: 2741
|
In reply to: Ridgeclimber, Styndall, Curt I just want to explain that when I think of FF I also think of Newton Law ( #3 , if I'm not mistaken ) The falling body doubles its waight for every meter of a fall, up to 173 times ( not exactly about that number ) so at the end of the fall a climber's body will waight ??? of kg. ( or pounds ), yet we still use a FF.
That's not exactly accurate, and the term 'weight' in this instance is kinda off.
Fall factor is not a measure of the force of a fall. That's what you're not getting. The fall factor provides information about the length of rope available to stretch and reduce the force involved with a fall as compared to the total length of the fall.
Fall factor is only a small component of the set of forces that goes into the total force of the fall, and therefor fall factor alone is not a useful piece of information by which to understand the breaking strength of a piece of gear.
Let me be clear here. Any force (like that on a piece of gear when a climber falls on it) will be measured in kilonewtons. Fall factor is not a measure of force, but rather a ratio that indicates the ability of the rope to absorb the force of the fall. The higher the fall factor, the smaller the amount of force the rope will absorb.
Fall factor alone tells you nothing about the forces experienced by the system.
|
|
|
|
|
brent_e
Apr 5, 2006, 5:38 AM
Post #20 of 36
(1971 views)
Shortcut
Registered: Dec 15, 2004
Posts: 5111
|
In reply to: Fall factor alone tells you nothing about the forces experienced by the system.
Hi Styndall,
not sure I agree with you here. If you have a fall factor of 0.1, for example, you know that the piece that caught that fall did not experience as much force as a piece of pro that cought a factor 1.6. The more rope you have in the system and the shorter the fall the less force will be exerted on the piece that caught the fall and the rope.
I think that is correct.
maybe not. flame me if not! 8^)
Brent
|
|
|
|
|
styndall
Apr 5, 2006, 5:53 AM
Post #21 of 36
(1971 views)
Shortcut
Registered: May 29, 2002
Posts: 2741
|
Pretend you have two fall situations.
Situation 1 has fall factor .1.
Situation 2 has fall factor 1.5.
Which system experienced the greatest force? You have no idea.
Fall factor alone provides no information as to the forces in a system.
If I hold a 24 inch sling by one end, clip a carabiner to the other end, then raise and drop the biner, my arm has just held a factor 2 fall. If I rig some industrial cable to thirty foot steel shafts driven into the side of a mountain, then attach my car so that when I drive off a cliff, the car falls 10 feet onto a hundred feet of cable, the fall factor is .1. However, in spite of the first situation having a factor 2 fall and the second having a factor .1 fall, the anchors in the second situation experience forces orders of magnitude greater than my arm does in the first situation.
If you know that two situations were identical except for the fall factor, then you can make some claims about the various forces. Even in climbing situations, where the setup will generally be fairly similar, fall factor might be misleading. A screamer and a very dynamic belay might well mean the force felt by the top piece in a fall with a high fall factor would turn out less than in a fall with a lower fall factor but a static belay and no screamer.
This is the point I'm trying to make.
|
|
|
|
|
patto
Apr 5, 2006, 8:03 AM
Post #22 of 36
(1971 views)
Shortcut
Registered: Nov 15, 2005
Posts: 1453
|
By those who don't know better, it is often thought that the fall length is an important factor in the force in the system. Most climbers know that this is not the case. That is why we talk about fall factors. It is the fall factor that is important and not the fall distance.
Of course the overall force also depends on the weight of the falling mass. In climbing the falling mass is usually roughly known ie between 50-100kg. Thus fall factor is the most important metric that determines the forces in the system.
|
|
|
|
|
heiko
Apr 5, 2006, 9:07 AM
Post #23 of 36
(1971 views)
Shortcut
Registered: Mar 3, 2005
Posts: 1505
|
In reply to: Based on the WC cam angle of 13.75 we can work out the grip strength. (ignoring the spring tension which is negligable once proper load is applied) Load Expansion pressure on rock (spread over all cams) 0kN 0kN 0.1kN 0.409kN 1kN 4.09kN 10kN 40.9kN
Would you mind posting the formula you're using to calculate this?
|
|
|
|
|
chossmonkey
Apr 5, 2006, 10:27 AM
Post #24 of 36
(1971 views)
Shortcut
Registered: Feb 1, 2003
Posts: 28414
|
In reply to: Pretend you have two fall situations. Situation 1 has fall factor .1. Situation 2 has fall factor 1.5. Which system experienced the greatest force? You have no idea.
Correct me if I am wrong.
In a typical climbing situation with a dynamic rope, and using the same climber taking the whip, the FF 1.5 is ALWAYS going to create more force than a FF 1.
How much force a given FF creates largely depends on the rope and its ability to absorb energy.
There is a long list of other variables that make calculating actual real life fall forces more of an estimation than anything else. Trying to do anything other than an estimation seems rather pointless.
|
|
|
|
|
reg
Apr 5, 2006, 12:58 PM
Post #25 of 36
(1971 views)
Shortcut
Registered: Nov 10, 2004
Posts: 1560
|
In reply to: (pushes his glasses up onto his nose) actually the myth that the harder a cam is pulled the harder it grips is incorrect. :
the lobes absolutely push against the rock harder as you pull on the cam.
In reply to: the whole concept of the cam is based on an optimum friction angle which is why the cam has that nice organic flared shape, it is based on natural shapes like shells that grow at a constant angle. the guy that created the first camming device (Jardine?? i think) was a smart dude he figured that the optimum angle for maximum friction was somewhere between 11 and 14 degrees so he set the constant angle of the camming device to a range of these "friends" and then tested them to find out what the best angle is this is why smooth cams hold better or at least as well as grooved cams, smooth ones have more surface area in contact with the rock, therefore more friction......:
more friction cause they push harder as there pulled
........In reply to: i dunno but for my own piece of mind I'm going to rationalize the hell out of this.....either that or throw out all my gear and take up golf........ :lol:
you got that right brother
|
|
|
|
|
|
|
|
|
1
