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Chockstone Forum - General Discussion

General Climbing Discussion

Author

Would you climb above this?

Penny

8/06/2012
11:43:47 AM

On 8/06/2012 kieranl wrote:

>I think you're quite wrong. Any load on the hex will tend to compress
>the cam, which has no resistance to compression, fatally weakening the
>placement. Just because the hex has a cord on it doesn't mean it should
>be used.
>I'll see if I can try it out this afternoon and let you know (day off
>:) )

If you're a fatty like me I bet you'll fatally weaken the system with any load on the cam too! Do be careful :)

Olbert

8/06/2012
11:52:53 AM

As for an actual physical analysis (assuming you weight the cam, weighting the hex would be suicidal)

First: Friction

Cams rely on friction to work, if the coefficient of friction is not high enough between the aluminium cam and aluminium hex then the cam will slide right out (the concave hex *might* stop this). Despite my initial gut feeling the coefficient of friction between aluminium and aluminium is roughly four times that of aluminium and rock. That means cams would work four times better if placed in an aluminium crack than a rock crack!

So there are no worries about sliding.

Second: Stability

Before weighting anything the hex is held in place by being pushed against the rock by the cam (and vica versa). The force of this push is dependant mainly on the strength of the springs inside the cam. If the springs are strong enough the rig will stay in place in a static situation. If the hex is too heavy it will fall apart before you can set it properly. It's pretty apparent that in this case the cams springs are strong enough.

Third: Weighting

What happens when you weight it? Well as any quick googling of cams will tell you, all the downwards force is opposed by the upwards holding force. The upwards holding force is made up mostly of two equal and opposite forces pushing outwards with only a little bit in the downwards direction.

Side note: Pulling 1kn down on a cam in a parallel crack will result in a the cam pushing outwards at 1000/(sin(alpha)) where alpha is the caming angle, normally approximately 14 degrees. So the outwards force is ~4.1kN.

If the direction of that outwards force which originates from the point of contact between the cam and the hex runs through the point at which the hex is flush with the rock, then everything is stable. If it runs below the section of hex/rock contact then the whole thing is going to want to roll downwards in an exploding manner when weighted. (This would be much simpler with a drawing but that's way to much effort.)

On the face of it, a strong tug would show you whether or not it's stable because nothing is going to slide (coefficients of friction are too high).

All that said, I would imagine the whole set up to get super untrustworthy with any movement. I would be putting at least a standard sling on the cam so that it doesnt move and be super careful not to knock it whilst climbing past. I would also be crying.


cruze

8/06/2012
11:57:32 AM

If I had to think that much before placing gear I'd be crying too!


Big G

8/06/2012
12:01:52 PM

I reckon the whole thing would look a lot more bomber (if at all!) if the hex was placed upside down. the cam would sit a bit better against the hex and might seat it a little bit better with the wider part of the hex at the bottom.

maadness

8/06/2012
8:48:27 PM

Could this be the start of a 'how many pieces of gear can you jigsaw together' competition?

kieranl

11/06/2012
5:08:46 PM

Did a little light testing this evening. I used one of the old-style 11 hexes with straight sides. The placement was OK but not ideal, the hex didn't sit neatly for it's full length.
I first tried it with the hex in its normal orientation when used as a nut (as shown in the first photo in the thread). I then put the hex "upside down" (see crappy photo here, sorry my phone is very old and camera poor).
1. Any weight on the hex caused the placement to fail.
2. With hex In "normal" orientation the placement held some weight and survived a gentle bounce test. It then failed a more slightly robust bounce test.
3. With hex in the "upside down" position the placement held a more vigorous bounce test than the "normal" one failed at. The hex tries to rotate on the bottom edge which looks quite spooky. Also note that the cam has the 2 inner cams against the hex rather than the outer ones. It may not make a difference but it seemed to me that this orientation might have a little more tolerance.

My testing was fairly limited as the location didn't lend itself to full-on bounce testing but it would definitely be an OK aid placement, probably about M3 if it was in the middle of a string of solid placements. You would definitely worry about security.
Would I free-climb above it? I'd prefer not to as it doesn't appear very stable. I would be terrified if I had to lower from it. If you're actually carrying hexes, stacking 2 hexes together would be a better proposition then this as they can be very secure.


Miguel75

11/06/2012
7:09:08 PM

Thanks for taking the time to test it out Kieran, I was out playing at WG today but forgot to give it another crack...

And I like to idea of a 'pro stacking' contest. I want to see a pic of stacked RP's;)


shortman

11/06/2012
7:14:20 PM

Thanks Kieran x2.

Mike- we gotta communicate more. I self belayed today, did u?


Miguel75

11/06/2012
7:15:11 PM

Nah buddy, climbing with Bigchris and some other friends... Where were you playing?


shortman

11/06/2012
7:45:09 PM

On 11/06/2012 Miguel75 wrote:
>Nah buddy, climbing with Bigchris and some other friends... Where were
>you playing?

Merri Creek - dodging blocks....don't ask...


Ben_E

11/06/2012
8:23:13 PM

On 11/06/2012 shortman wrote:
>
>Merri Creek - dodging blocks....don't ask.

Not just downstream from the High street bridge next to the wooden footbridge and palm tree, by any chance?

That pile of choss is about to become my local "crag" when I move in 2 weeks - I was looking at it the other day trying to decide whether bouldering on it would be merely silly or outright suicide...


shortman

11/06/2012
8:31:41 PM

Na. But that spot has one hell scary overhang. Pulled huge chunks off in the past.

Further down, on the other side there is an old quarried wall. 15m of crap and 2m of okness. Not worth the faff around.


shortman

11/06/2012
8:33:10 PM

Great spot to live BTW. Don't worry too much about the commission flat folk....just keep ya bike hidden and locked up.


Ben_E

11/06/2012
8:58:12 PM

On 11/06/2012 shortman wrote:
>Na. But that spot has one hell scary overhang. Pulled huge chunks off in
>the past.

Ah. So more or less suicidal, then. Excellent!


shortman

11/06/2012
9:01:53 PM

On 11/06/2012 Ben_E wrote:
>On 11/06/2012 shortman wrote:
>>Na. But that spot has one hell scary overhang. Pulled huge chunks off
>in
>>the past.
>
>Ah. So more or less suicidal, then. Excellent!

Pretty much....enjoy!


Ben_E

11/06/2012
9:02:05 PM

On 11/06/2012 shortman wrote:
> Don't worry too much about the commission flat folk....

You're assuming I'm not moving into them (I guess the advice would be the same either way)! Hadn't even occurred to me to worry about that, clearly I'm naive...

Will have an undercover garage under the house with plenty of room for the bikes and boats, so probably not much of a concern anyway.

dalai

11/06/2012
9:20:40 PM

On 11/06/2012 Ben_E wrote:
>That pile of choss is about to become my local "crag" when I move in 2
>weeks - I was looking at it the other day trying to decide whether bouldering
>on it would be merely silly or outright suicide...

Suicide and silly...

There are one or two (can't recall the number) very small and very limited blocks below Oldis park that was dubbed the Junkie's Lair due to the used syringes around! And no it wasn't me - syringes, name or having climbed there...

There is better basalt in the area. Both quarried and natural.

Curious as always where you were pulling blocks shortman. ;-)


shortman

11/06/2012
9:28:23 PM

Just pass Heidleberg RD Bridge goin downstream towards the yarra on the eastern side is a small quarried section about 30m from the creek. Almost 20 meters high, it used to have rap chains at the top.

Cam McKenzie

12/06/2012
7:46:07 AM

On 11/06/2012 shortman wrote:
>Just pass Heidleberg RD Bridge goin downstream towards the yarra on the
>eastern side is a small quarried section about 30m from the creek. Almost
>20 meters high, it used to have rap chains at the top.

Next to the maze thing made out of blue stone blocks? Covered in blackberries? I've run past there many times thinking there may be one or two lines up there that weren't complete choss but have never been psyched enough to actually bother looking.


shortman

12/06/2012
9:28:56 PM

On 12/06/2012 Cam McKenzie wrote:
>On 11/06/2012 shortman wrote:
>>Just pass Heidleberg RD Bridge goin downstream towards the yarra on the
>>eastern side is a small quarried section about 30m from the creek. Almost
>>20 meters high, it used to have rap chains at the top.
>
>Next to the maze thing made out of blue stone blocks? Covered in blackberries?
>I've run past there many times thinking there may be one or two lines up
>there that weren't complete choss but have never been psyched enough to
>actually bother looking.

Na, further upstream heading away from the yarra on the other side. But I know the bit you mean with berries and blocks.

There are 40 messages in this topic.