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braaaaaaaadley
Oct 24, 2003, 7:06 PM
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I hear that while placing cams as a rule of thumb, you should place them b/t 75% open and 25% closed. Its obveous that unless your cam has cam stops you should not place them above 75% generally b/c your placement will ether fall out or become a 50+ dollar nut; but the other day I was forced into placing a 1.5 friend definetly smaller than the 25%. Are there any other disadvantages to this type of placement other than the cam getting stuck?
Thanks!
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dingus
Oct 24, 2003, 7:10 PM
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In reply to: I hear that while placing cams as a rule of thumb, you should place them b/t 75% open and 25% closed. Its obveous that unless your cam has cam stops you should not place them above 75% generally b/c your placement will ether fall out or become a 50+ dollar nut; but the other day I was forced into placing a 1.5 friend definetly smaller than the 25%. Are there any other disadvantages to this type of placement other than the cam getting stuck? Thanks!
The dirtier the inside of the crack, or the more slippery the surface for whatever reason, the more I tend to over cam.
Did a mild FA recently and seeminly every cam I placed was in the 25% or under range. Commented on this to my partner and he said the last two recent FA's he did it was the same.
In clean, antiseptic cracks like in Yosemite Valley, optimum placements abound. Scraping dirt, liches and loose flakes from the bowels of a virgin crack I want something that has a chance for a 2nd life when it starts to slide out.
Severe OVERcamming can result in not enough force being applied to the cam angle in the event of a fall, or just hopelessly stuck cams for the 2nd. But over camming isn't evil and there are times when I believe it to be a good thing.
Made MY sack feel better I know that
DMT
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squish
Oct 24, 2003, 7:14 PM
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75% open or 25% closed? You'd better make sure you have a lot of different sized cams if they only work in one size!
Sorry, couldn't resist...
The range is flexible. Basically, you should "try" to get a fit that is within the middle of the range. Too tight, and you can get hooked up on the smallest constriction and not be able to clean it. Too loose, and it gets walky, or just looks like it's going to fall out.
You should know for yourself when it's a good placement. The 25-75 is more of a rule-of-thumb, I guess.
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buckyllama
Oct 24, 2003, 7:14 PM
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No.
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braaaaaaaadley
Oct 24, 2003, 7:21 PM
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In reply to: 75% open or 25% closed? You'd better make sure you have a lot of different sized cams if they only work in one size!
I own seven cams. I had already used the other sizes around the one I placed that was below 25%. It was that cam or no cam, so i picked that cam!
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on_sight_man
Oct 24, 2003, 7:29 PM
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In reply to: I hear that while placing cams as a rule of thumb, you should place them b/t 75% open and 25% closed. Its obveous that unless your cam has cam stops you should not place them above 75% generally b/c your placement will ether fall out or become a 50+ dollar nut; but the other day I was forced into placing a 1.5 friend definetly smaller than the 25%. Are there any other disadvantages to this type of placement other than the cam getting stuck? Thanks!
Yes there is. There is not as much cam lobe touching the rock on a cam that is fully retracted. It's a math thing that I could explain if I really had to, but suffice it to say that at 50% open, the lobes of the cam are flatter against the wall then at 10% open. There's a tighter curve to the cam at 10% so less metal touches rock. This makes their holding power less. So even in soft rock, around 50% is best (though I'll grant you, bit tighter may be better, just not a lot)
Remember, mathematically, there may only be one "point" of contact between a perfectly flat, perfectly hard wall and the cam lobe. And mathematically, cams shouldn't work at all in parallell cracks because no amount of force laterally would keep you up vertically. But in reality, cams work on friction and the truth that more than one "point" touches the walls...
So all in all, use a smaller cam.
Edited to add---
For what it's worth, that's why Camalots have a larger range than other Cams. Because each side of the CAM has it's own axle, the angle made with the wall can be flatter across a wider range.
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geezergecko
Oct 24, 2003, 7:49 PM
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From the Black Diamond Camalot manual :
http://www.bdel.com/...15%20_b_camalots.pdf
"Ideally, each of the cams should contact the rock at lower to mid expansion range (50% to 90% retracted)"
"when given the choice, well-retracted cams make a better, more reliable placement than cams which are almost completely extended"
"A completely retracted Camalot can be very difficult to remove. Leave room for the cams to retract a little further, so your device can be retrieved" (duh!)
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imaclima
Oct 24, 2003, 7:57 PM
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In reply to: In reply to: 75% open or 25% closed? You'd better make sure you have a lot of different sized cams if they only work in one size! I own seven cams. I had already used the other sizes around the one I placed that was below 25%. It was that cam or no cam, so i picked that cam!
what he meant was 75% open=25% closed
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alpnclmbr1
Oct 24, 2003, 7:57 PM
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Camalots ideal range according to BD is 50% to 90% contracted
I seem to recall the figure for aliens being 80% retracted.
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on_sight_man
Oct 24, 2003, 8:06 PM
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In reply to: From the Black Diamond Camalot manual : Ideally, each of the cams should contact the rock at lower to mid expansion range (50% to 90% retracted)"
Wow, I didn't realized Camalots were designed for up to 90% retracted. Regardless though, my point holds. If you have to choose between a cam that is 90% retracted, or one that's 50% retracted, I'd go with the 50% all other things being equal. Problem is, all other things are never equal (lobe width for example)
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trad_mike
Oct 24, 2003, 8:31 PM
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Sorry, if you're placing cams that are only 25% retracted, those placements are sketch. Rule of thumb is 40% to 90% retraction. Most placements with a noticable amount less than 40% retraction are unsafe. The usable range of a cam is much much less than the min and max range that you see in the specs.
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helmut
Oct 24, 2003, 9:51 PM
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All very good points, the ideal placement is textbook and when it happens is like a thing of beauty that you want to photograph and show to everyone that it does exist!!
Some additional points in favor of squeezing the cam in there...All cams are built off of the spiral of archimedes and a constant camming angle, usually around 14 degrees, that determines the radius of the spiral. The unique property of the spiral of archimedes is that regardless of the expansion of the cam the angle of the force remains constant. So long as the coefficient of friction of the rock is greater than the tangent of the camming angle the cam will hold, that is why manufactures will always recommend to squeeze it in tight because it is just as safe and has less chance of walking out of the crack completely. The most common failure of a cam is from the outward force of the cam on the rock actually destroying the surrounding rock!
Interesting to note that the tangent of 14 degrees is 0.249. The coefficient of aluminum on rock is approximately 0.3. So lets see, hmmm 0.3 is greater than 0.249 so you're all set (but not by much!!)
I think I need to work on my chockstone girth hitching techniques.
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afiveonbelay
Oct 27, 2003, 6:51 AM
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In reply to: The most common failure of a cam is from the outward force of the cam on the rock actually destroying the surrounding rock!
well said
inspect the adjacent rock. cams can exert outward forces that can leverage out broken blocks or crush the matrix at the lobe face/rock point of contact
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on_sight_man
Oct 28, 2003, 1:08 AM
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In reply to: So long as the coefficient of friction of the rock is greater than the tangent of the camming angle the cam will hold, that is why manufactures will always recommend to squeeze it in tight because it is just as safe and has less chance of walking out of the crack completely.
The coefficient of friction may be the same, but the amount of lobe resting on the rock is different at %50 than at %90. Have you ever taken an overcammed Cam out of rock in Indian Creek? You can almost slide them out without retracting them because the wals are so flat and the spirals so tight that there's no friction.
I'm not saying to go outside manufacturer recomendations. I wonder whether the truth is that there is one sweet spot (probably halfway between the two extremes) and it just drops from there either direction?
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ep
Oct 28, 2003, 2:55 AM
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Intuitively I feel that the best placements are close to fully retracted while leaving enough range in order to clean the piece. But that's just my intuition based on years of climbing. I could be wrong. What really works best?
on_sight_man claims that there is less cam on the rock as the cam is retracted. Since the radius is less, one might expect this. But how much difference is it really and how important is this for holding power? Another factor to be considered is that the springs holding the cam against the rock will be tensioned more as the cam is retracted. Again, I don't know how much this matters.
For what it's worth, here is a snippet from Black Diamond.
(http://www.bdel.com/custserv/faq.html)
"Q. How far should I retract my cams for the most solid placement?
A. In almost all situations, provided the placement is sound (good rock, not too slick or flared), a Micro Camalot of size .3 and above, will likely be reliable when fully retracted (only problem here is that the unit may be hard to remove) to 25% retracted. With the .1 and .2 Camalots being so small, they start to lose the ability to hold a fall at about 40% retraction."
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helmut
Oct 30, 2003, 5:08 PM
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That's a good point OSMan, all other things being equal there will be less rock contact with the cams squeezed in there. But I still have to say better squeezed in there at 90% than trying to find the 50% placement, because if the 50% placement goes to 30% you could be looking at trouble where as the margin of error at 90% seems greater, even if it goes to 100% and gets stuck, I'd rather have to replace a cam than an ankle or worse!
I have never climbed a splitter crack like the ones in Indian Creek, I climb mostly in Eldo, so I don't even really know what crack climbing is like.
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tt
Oct 31, 2003, 2:33 AM
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For the most part, I use the 50-90% closed rule. I definitely try to do this with the smaller cams, especially aliens, where I like to go 75% closed or more with the smallest sizes. There's just not that much difference in crack width between 50% closed and 100% open, so I like to err on the side of caution.
If people make a habit of making bad cam placements and using the excuse that it's better than nothing, then they may end up like the poor Australian girl with the zippered cams (or worse--let's learn from that!). I would say learn to place more passive to save the cams for those must use occasions, or beg/borrow/buy to fill in the rack for a particular climbing area.
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curt
Oct 31, 2003, 2:56 AM
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In reply to: For what it's worth, that's why Camalots have a larger range than other Cams. Because each side of the CAM has it's own axle, the angle made with the wall can be flatter across a wider range.
Curt
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ronamick
Oct 31, 2003, 3:09 AM
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It's nice to have the option of optimizing your placements like that, but if you have the time to sit there and worry about your cams being within specified range, methinks you should try leading harder climbs. I am extremely pleased when I get pro that's going to hold a fall. Once the cam is in, my thoughts tend to9 turn to the next move and the next pro.
If a cam goes in, it will come out. You try not to bury them, but your priority is protection, not ease of removal. They make handy cam retrieval devices to remove cams that are buried. Wired stopper cables on the trigger stems can be used too.
A bigger concern is undercamming, where the cams are barely retracted.
Cams have little strength as a nut, and can "umbrella" if pulled all the way open under pressure. I'd rather have mine crammed in tight or even fixed, because then they will still do the job. Another dangerous placement is a shallow cam in a horizontal crack, which can lever hard on the stem. Cable stem cams eliminate this problem, however. Tying off the stem is a good idea for rigid stems. But % of camming is a new one on me.
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on_sight_man
Nov 1, 2003, 12:24 AM
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[quote="curt"]In reply to: Because each cam follows a section of a logarithmic spiral, the expansion rate is completely independent of whether there is one axle or two axles. The Camalots have a greater range because BD trades off holding power (smaller angle) for range (larger angle). This can also be accomplished with single axle units, or for that matter with straight sided stoppers. Curt
I don't think this is the main thing. If you're looking at the cam sideways, the right hand lobe has the axis on the left hand side of the cam. Given the mathematical construction of a cam and the constant angle, it's easy to see that there is more cam lobe (a looser spiral) than if the axle was moved to the center of the cam. This gives more lobe on the rock at more retracted position and so the range increases. They may also play with the angle of the spirals tangent, but that's not the main thing.
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on_sight_man
Nov 1, 2003, 12:27 AM
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In reply to: even if it goes to 100% and gets stuck, I'd rather have to replace a cam than an ankle or worse!
As long as the result is the cam just getting stuck. Like I said, in sandstone, the result can be the cam sliding right out of the rock because there's not enough lobe on the rock.
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brutusofwyde
Nov 1, 2003, 4:55 PM
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In reply to: Like I said, in sandstone, the result can be the cam sliding right out of the rock because there's not enough lobe on the rock.
Depends on the sandstone. The mode of failure I have seen most often in sandstone is the cam ripping through the stone for a foot or more, leaving parallel gouges in each side of the rock.
A perfect tangent touches a perfect circle at only one point, regardless of the diameter of the circle.
To paraphrase Helen Keller:
Perfect generalizations regarding cam placement do not exist in Nature. Life is either a daring adventure, or nothing.
Brutus, who crams the cams when on unclimbed rock.
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micronut
Nov 1, 2003, 5:38 PM
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It all depneds on how gripped I am. I'll shove in a tight cam, knowing it's gonna be hard to clean when I'm stressed. I don't wanna pick through the rack if the placement is a little tight, just clip and go and let the second worry about it. My experience is that camalots are a little more forgiving of over-camming than friends or metolius.
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braaaaaaaadley
Nov 1, 2003, 10:12 PM
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Thanks for all of the responses. It seems to me that there are many diffrent opinions on this subject out there. The cam manufacturers should be more specific about what will happen if you dont place it at its optimal range. They should say what will happen like if you over place a cam it will result in the cam falling out and your death so then people will know not to do this. Just my opinion...
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gyngve
Nov 3, 2003, 6:11 AM
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In reply to: Thanks for all of the responses. It seems to me that there are many diffrent opinions on this subject out there. The cam manufacturers should be more specific about what will happen if you dont place it at its optimal range. They should say what will happen like if you over place a cam it will result in the cam falling out and your death so then people will know not to do this. Just my opinion...
Many manufacturers do recommend that you err on the over-cammed side for microcams.
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