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Cams Ripping At Arapiles - common?

GerryN

12-Oct-2009
10:46:07 AM

Has anyone found that cams sometimes rip out on falls at Arapiles? Not sure if the glassy, hard rock has anything to do with it, or I just placed a bad runner. I had two cams on Trojan above the last good wire about 2m below the peapod. A purple 0.5 camalot was deep in what seemed to be a perfect placement just above the handjam, and a smaller grey camalot in a more marginal placement on the bulge above it (taking a solid downward tug). I fell out of the peapod and both cams ripped, and went for a big whipper. I don't think the crack for the 0.5 purple cam flared inside and it seemd to be bomber so it was a complete surprise to me when it ripped. In a similar crack on Tas dolerite which I'm used to, a placement like this would not rip out. Maybe I just placed a dodgy piece but has anyone else encountered this at Araps? Has rock type got anything to do with holding power of cams?


Robb

12-Oct-2009
10:54:40 AM

ive heard of a few people ripping cams on trojan before. think it might be the glassy nature of some of the rock.

Tlockwood

12-Oct-2009
10:58:15 AM

I've heard likewise, the glassy/slick rock allowing them to pull out.

patto

12-Oct-2009
11:15:10 AM

Did you tug on the piece before you clipped? Tugging is a good start to testing whether the piece will start to slip or not. Piecesripping is hardly common but I have heard of it happening.

BD Camalots have 9% less holding pressure than most other cams such as DMM, WC. 12% less than metolius. Considering the slip/noslip condition is usually very marginal it would be likely that an alternative brand cam might have held just fine.
*The bulk of my racks made of BDs, im not trying to rag on BDs.

One Day Hero

12-Oct-2009
1:26:54 PM

Cams need friction to hold, araps rock is nearly as bad as limestone for friction.....that's why wires should always be the #1 option there. I had a swedish mate rip a good looking cam out of Trojan resulting in him hitting the deck.

If you can find the wires in that bit of the crack, they are super extra good.....just that you need eyeballs on stalks to be able to spot them easily


Richard

12-Oct-2009
2:15:18 PM

On 12/10/2009 GerryN wrote:
>Has rock type got anything to do with
>holding power of cams?

Some interesting quotes from on line searches:

"CAMS were developed in the 1970s for the smooth parallel sided cracks of Yosemite" - see on line page 89 "Guide to Climbing By Tony Lourens" http://books.google.com.au/books

According to http://web.mit.edu/custer/www/rocking/cams/cams.body.html a cam will fail in a parallel crack if tangent of the angle between the cam's contact point with the rock, and the axis if rotation of the cam is less than the the coefficient of friction.

(Essentily the same info / explanation exists at wikipedia - http://en.wikipedia.org/wiki/Spring-loaded_camming_device but they omit the info on the maximum force the cam will hold - a vital part of the consideration.)

What this means is, the smoother the rock, the lower the angle of beta needs to be (a more open placement is required), for the cam to carry its maximum load (eqn 2). But the lower the angle of beta, the lower the maximum force that this cam will hold is. (eqn 5).

So as rock gets smoother and smoother, you want to place the cam with a more and more open angle, so it will carry the maximum force it can, but that maximum force is getting gettting lower and lower.

That's what the theory says...

gfdonc

12-Oct-2009
2:53:32 PM

I think Patto has a point. BD Cams get a wider expansion range but at the expense of security. Friends were originally developed in Yosemite granite but with an adequate safety margin.

My recollection of the BD cams is that the cam angle changes as the cam gets closed down, so placing units with the cams more widely open is likely to give better holding. This somewhat negates the wider expansion range. However I'm unsure of this point, someone will need to confirm.

I'm glad you were well backed up enough to take such a fall without injury.

rightarmbad

12-Oct-2009
3:29:12 PM

Black Diamond cams are constant cam angle.
It is the cam angle that needs to change, not how far open or closed the cam is.

If more bite is required, softer lobes ( Aliens ) or different cams with an angle that places more outward force on the rock are what is required.

Why is it that people have such misconceptions about the workings of a simple cam.......

patto

12-Oct-2009
3:38:31 PM

On 12/10/2009 gfdonc wrote:
>I think Patto has a point. BD Cams get a wider expansion range but at
>the expense of security. Friends were originally developed in Yosemite
>granite but with an adequate safety margin.
>
>My recollection of the BD cams is that the cam angle changes as the cam
>gets closed down, so placing units with the cams more widely open is likely
>to give better holding. This somewhat negates the wider expansion range.
> However I'm unsure of this point, someone will need to confirm.
>
>I'm glad you were well backed up enough to take such a fall without injury.
>

BD C4s still have constant contact angle of 15 degrees. The only cams to my knowledge that have a variable angle are Metolius Supercams. (Of course aliens have been found to have a variable cam angle but that is due to sloppy manufacturing!)

On 12/10/2009 Richard wrote:
>On 12/10/2009 GerryN wrote:
>>Has rock type got anything to do with
>>holding power of cams?
>
>Some interesting quotes from on line searches:
>
>"CAMS were developed in the 1970s for the smooth parallel sided cracks
>of Yosemite" - see on line page 89 "Guide to Climbing By Tony Lourens"
>http://books.google.com.au/books
>
>According to http://web.mit.edu/custer/www/rocking/cams/cams.body.html
>a cam will fail in a parallel crack if tangent of the angle between the
>cam's contact point with the rock, and the axis if rotation of the cam
>is less than the the coefficient of friction.
>
>(Essentily the same info / explanation exists at wikipedia - http://en.wikipedia.org/wiki
>Spring-loaded_camming_device but they omit the info on the maximum force
>the cam will hold - a vital part of the consideration.)
>
>What this means is, the smoother the rock, the lower the angle of beta
>needs to be (a more open placement is required), for the cam to carry its
>maximum load (eqn 2). But the lower the angle of beta, the lower the maximum
>force that this cam will hold is. (eqn 5).
>
>So as rock gets smoother and smoother, you want to place the cam with
>a more and more open angle, so it will carry the maximum force it can,
>but that maximum force is getting gettting lower and lower.
>
>That's what the theory says...
>
>

If by a 'more open angle' you mean a cam that is wider within its expansion range then that is incorrect. The whole design of cams is that they have a constant contact angle.

egosan

12-Oct-2009
3:43:52 PM

It is my understanding that the Metolius cam use a 13.25 degree angle. Giving them
greater holding power but smaller ranges than WC cams at 13.75 degrees and BD cams
at 14 degrees. With the exception of the SuperCam which has the asymmetric lobs to
increase the range.

There is a lot of hearsay about cam angles out there. I am still looking to find definitive
cam angles for the major manufacturers. Patto, I have not seen 15 degrees anywhere for
BD gear. However, I may very well be full of shit.


ajfclark

12-Oct-2009
3:56:14 PM

From the cam angle testing site:

13.25/Metolius
13.75/Wild Country
14/Trango
15/Black Diamond
16/CCH Aliens

From memory the guy that wrote the software (John Field) designed cams and I figure if he can write the software to predict cam angles from photos of the lobes he's probably got the maths down pat.

[Edit: It was the Metolius Super Cam that he designed ]

egosan

12-Oct-2009
4:11:43 PM

Thanks for that, Andrew.

One Day Hero

12-Oct-2009
6:00:08 PM

And the other imporant bit is the frictional properties of the metal in the cam lobes and of the rock. Despite being smooth, yos granite still has greater coefficient of friction with aluminium than limestone does (almost certainly greater than araps quarzite does too, given how cams behave there)

The brand of cams used is less important than which bits of rock you stick them in. At araps, look for enclosed pod placements.......or better yet, ditch the pricey, heavy seppo technology and substitute a good ol' fashioned wire whenever you can.

One Day Hero

12-Oct-2009
6:04:02 PM

On 12/10/2009 Richard wrote:
>According to http://web.mit.edu/custer/www/rocking/cams/cams.body.html
>a cam will fail in a parallel crack if tangent of the angle between the
>cam's contact point with the rock, and the axis if rotation of the cam
>is less than the the coefficient of friction.

Don't make it more complicated than it is. All the above quote is saying is: if the rock is so slippery that you don't trust that your feet will stick, don't trust your cams to stick either!

gfdonc

13-Oct-2009
9:32:01 AM

Hexes are underrated.

another dave

13-Oct-2009
10:36:46 AM

> 13.25/Metolius
> 13.75/Wild Country
> 14/Trango
> 15/Black Diamond
> 16/CCH Aliens

What about HB? Nobody like HB anymore?

Hexes are awesome. Especially plastic ones.
So does anybody know the camming angle on a good old fashioned WC slung Hex :p


nmonteith

13-Oct-2009
10:54:42 AM

On 13/10/2009 another dave wrote:
>What about HB? Nobody like HB anymore?

HB went out of business several years ago.


ajfclark

13-Oct-2009
10:58:18 AM

Send me a profile photo of the lobes on a HB cam and I'll see if John's software can pick the cam angle.

robbio

13-Oct-2009
5:38:12 PM

I also had two cams pull out on me at Arapiles which suprised the hell out of me. See my recent post "Overcammed cams pull out at araps". They both seemed like good placements, even if abit overcammed. I have also heard several stories of cams failing on the same climb, I assume it must be an especially glassy crack which doesn't like cams...


IdratherbeclimbingM9

13-Oct-2009
5:42:08 PM

On 13/10/2009 robbio wrote:
>See my recent post "Overcammed cams pull out at araps".

Link

There are 30 messages in this topic.