How do Horizontally placed Cams Work?

Christian Fracchia wrote:...your free-body diagram is missing the normal force on the stem (from the rock edge) which requires considering the moment-arm. There is additional non-negligible friction at that point.

I wondered about this, but I don't think that you can consider a flexible cable as providing a moment arm. But even if the stem is rigid, the fact that it is resting on the bottom edge of the crack means there is no net torque around that point. I think the situation is more like a pulley with friction. (PS: one of the things that makes the account hard to interpret is that it isn't a free-body diagram.)

Christian Fracchia wrote:...regarding the experimental set-up the steel simulator is going to flex substantially more than rock. This affects the normal force while engaging friction.

This is and important observation, and was the source of an error about the performance of Metolius cams in horizontal placements a while back.

Christian Fracchia wrote:...as you admitted in your video the coefficient of friction of aluminum-rock and aluminum-steel are not the same.

True, but the point was that the cam held when pulled directly out but not when loaded perpendicular to the crack, so it is the difference in behavior at different loadings that is of interest, not the actual pull-out numbers. The trouble is that the results could just be the result of the "crack walls" flexing. (We might also ask whether the downward and outward jerks were really of the same magnitude...)

I'm still going to try to work out the math to my own satisfaction, since I agree with Chris24Graham that their seem to be problems with the analysis in the video. Meanwhile, Chris F. is right about the anecdotal evidence for cams in horizontals, which at this point is extremely strong. Still, there are times when such cams seem to fail inexplicably---for example the relatively recent accident on CCK direct in which a really critical and absolutely perfect (but smooth) cam placement failed. We can always chalk such things up to the mysterious vagaries of nature, but it would be much better to have an intelligent framework for thinking about them, and the asymmetric loading of the cam lobes in horizontal placements is, in my opinion, at least worth thinking about.

Trigger wires would get pulled toward the cam lobes, not in the direction that's required for retracting.

christian-fracchia:

Thank You! Thank you for trying this out. Especially for braving the January weather. My only critique is judging from the video, the yanks seem pretty pretty weak. I realize that's hard to judge from a video but I feel comfortable saying I pulled a lot harder in my tests. Still, it's a great contribution to the conversation.

Other factor worth noting, and you as well as others mentioned, the grain/texture of the surace of the rock and lobes makes a difference. Otherwise, there would be no tread pattern on the lobes even though the model suggests it wouldn't make a difference. The slot I try in on Carbs seems more smooth them the one you tried.

Still, Thank you for the insight.

youtu.be/FDr4mYc0gr4

It does bro. I did my own test and none of the cams failed. I would expect a disclaimer from the manufacturers if cams sucked at horizontals.

Randomdiscourse wrote: The slot I try in on Carbs seems more smooth them the one you tried. Still, Thank you for the insight.

Unless I missed something, you didn't actually try the slot on Carbs. You didn't fall on it in the field video. You recreated it at home with two plates of steel. Suggesting that two plates of steel is a better representation of the slot on Carbs, instead of an actual smooth horizontal composed of the same stone, is ludicrous.

Fehim Hasecic wrote:It does bro. I did my own test and none of the cams failed. I would expect a disclaimer from the manufacturers if cams sucked at horizontals.

Err...did you ever actually read the manuals?

demandware.edgesuite.net/aa…

Ted Pinson wrote: Err...did you ever actually read the manuals? demandware.edgesuite.net/aa…

The only thing I see there is a disclaimer to inspect if loaded over an edge (check for kinking). Nothing about the actual placement being bad.

I interpreted that as "use caution with horizontals...for example, kinking."

Rob Subry wrote:The fact is; Cams are not the best option for horizontal placements.

Why do you say that?

Rob Subry wrote:That being said, Aliens would be the preferred cam for such a placement

Again what basis for this is there? The characteristics of aliens, (soft lobes and wider camming angle) don't give them an advantage in horizontal cracks.

I place horizontal cams all the time. I rest and fall on them many times. I've never had a reason to worry. I've even taken falls on blindly place horizontal pieces.

Personally I often find horizontal pieces MORE trustworthy as there is often less possibility of the cam walking.

Err...did you ever actually read the manuals?

I did actually. Nothing about not placing cams in horizontals, just to inspect the steam if you fall on it because it "might" get damaged.

rgold wrote:I still suspect that the jerk test will turn out to be as good a field test as you can manage.

rgold wrote:However, the theoretical considerations about holding being independent of load indicate that the solidity of the cam ought to be checkable by a vigorous jerk.

And from what I conclude this theoretical test is pretty damn reliable with just several caveats. (weak rock, flared placements etc...)

It seems this basic field test simply isn't done as often as I would expect. I pretty much do a token pull for all my placements and a vigorous one for the ones I'm less trustful about.

Once my token pull caught me by surprise though. When a seemingly good placement was actually part of a weak flake that didn't look like a flake. The flake moved and the cam popped. I was pretty glad of that as that was going to be my next foothold.

patto wrote: Why do you say that? Again what basis for this is there? The characteristics of aliens, (soft lobes and wider camming angle) don't give them an advantage in horizontal cracks. I place horizontal cams all the time. I rest and fall on them many times. I've never had a reason to worry. I've even taken falls on blindly place horizontal pieces. Personally I often find horizontal pieces MORE trustworthy as there is often less possibility of the cam walking.

1 In many ways, tri-cams are better suited for horizontal cracks than SLCDs. Whether you using them or not, they often perform better in horizontals and the equivalent sized SLCD.

2 I'm gonna guess he was referring to the flexible cable stem on aliens which many say is less prone to damage if loaded over and edge. I'm not quite sure I buy this as I've heard that the old forged friends with a gunks tie-off can perform better in horizontals than other cams.

patto wrote: Why do you say that? Again what basis for this is there? The characteristics of aliens, (soft lobes and wider camming angle) don't give them an advantage in horizontal cracks. I place horizontal cams all the time. I rest and fall on them many times. I've never had a reason to worry. I've even taken falls on blindly place horizontal pieces. Personally I often find horizontal pieces MORE trustworthy as there is often less possibility of the cam walking.

Flexible stems.

Eli: what the heck is a "Gunks tie off"?

Ted Pinson wrote: Flexible stems. Eli: what the heck is a "Gunks tie off"?

Ted Pinson wrote: Flexible stems. Eli: what the heck is a "Gunks tie off"?

Last time I checked most cams have flexible stems. Additional floppiness of the stem doesn't offer an advantage in the holding power as discussed here.

eli poss wrote:Whether you using them or not, they often perform better in horizontals and the equivalent sized SLCD.

Define perform better. In my experience an SLCD is holds securely in a horizontal and is easier to place and remove.

eli poss wrote:I'm gonna guess he was referring to the flexible cable stem on aliens which many say is less prone to damage if loaded over and edge.

I haven't had issues with damage from horizontals. But I hardly see that as a concern. Damage isn't failure.

rgold wrote:As I said in a short post after the long one, I have to redo (actually do, since I was just looking at a quick sketch) the moment balance calculations taking into account the crack wall reaction forces I ignored, so I'd take everything I said with a grain of salt, especially the parts about the cam angle and stem angles, which are wrong.

Getting back to this I did a more few quick calculations... And based on mine your gut was right with your geometry but measured from the wrong plane...

rgold wrote:Very simple geometry shows that the critical angle of "stem perpendicular to upper cam angle line" occurs when the angle the stem makes with with the bottom plane of the horizontal crack is equal to the cam angle. That's about 14 degrees, which isn't that much of an angle. Once your stem is at 14 degrees or more to the bottom of the crack, your cam, in theory, will not hold.

From my quick calcs you are right about the critical angle but it is measure from the VERTICAL plane. AKA the plane perpendicular to the horizontal crack. This leaves you with 76 degrees of stem angle. This is impossible to achieve with a regular crack. Which concurs much more sensibly with basic hands on experience with horizontal placements.

*When I say I did 'quick calcs' I took the lazy way out and used a computer. I used a statics computer program and observed the force reversal at the cam angle. (As would be expected from basic geometry.) I also observed consistent normalforce-friction ratio across the range so the coefficient of friction doesn't affect the calcs. (Of course the regular friction coefficient threshold still apply.)

That was my back of the envelope calculations. I believe they are valid. Feel free to correct if you have a bigger envelope for more rigorous calculations. :-)

eli poss wrote:

Ha, wow! That's wild. Wouldn't work with modern cams though, unfortunately. I can't help but feel like the perpendicular loading is problematic, though I suppose Rich et. al will run the numbers.

patto wrote: Define perform better. In my experience an SLCD is holds securely in a horizontal and is easier to place and remove. I haven't had issues with damage from horizontals. But I hardly see that as a concern. Damage isn't failure.

With cams you run the risk of damaging the cable if it runs over an edge and is whipped on. Damage isn't failure, but it costs money repair/replace. A webbing sling on a tri-cam doesn't really have that risk. Cams can walk and become undercammed or overcammed, which doesn't really happen to tri-cams.

Also, when you're dealing with less-than-perfect placements such as pockets, flares, funky pods, etc tri-cams tend to fit better than cams. They are also less likely to slip out of a placement in slick, greasy rock than SLCDs. And they're lighter and cheaper.

Randomdiscourse wrote:christian-fracchia: Thank You! Thank you for trying this out. Especially for braving the January weather. My only critique is judging from the video, the yanks seem pretty pretty weak. I realize that's hard to judge from a video but I feel comfortable saying I pulled a lot harder in my tests.

Ok, we were out again today and at the end of the day we decided to do some more yanking. This time we used body weight of a short 2-3ft fall on 2-3ft of rope and we found a mildly flared horizontal and placed the cams at the edge of where they would sit without falling out on their own.

I must say that doing this made me wonder how anyone pulls cams out of horizontals when the rock quality is good because we did a terrible job placing them...and they still held!

I would like to add that the climbs Tiers of Fear, Ozone, and Collect Calls all require extremely shallow cam placements. The placements are so shallow only one size can be used. Ozone and Tiers have seen repeated falls and I haven't heard of either of them ripping.

In the original question the horizontal on Carbs is indeed shallow, but there are no other options, so isn't it best to put the largest cam possible and try not to fall? In addition I don't think many people whip on that piece because the climbing above it is 5.9 but the runout is relatively long.

Without further ado...take two!

youtube.com/watch?v=fAvbzGv…