Working range of SCLDs

I own a full set of DMM 4CU and a set of BD Camalots (up to #3). While trying to figure out how to place my cams better I found different recommendations from different manufacturers:

Black Diamond: "Ideally, each of the cams should contact the rock at lower to mid expansion range (50% to 90% retracted)".
This totally makes sense because the more a cam is retracted, the more the spring will push it against the rock, increasing the friction that holds it in place, thus it's stability.

Wild Country:"Always ensure that all the cams make contact with the sides of the crack, preferably in the middle 1/2 of their expansion range (i.e. the cams should be between 1/4 to 3/4 open)".

This makes sense only from the UIAA point of view (UIAA125-EN12276 Frictional Anchors): "Position 1: s = bmin+[(bmax – bmin)/4]; Position 2: s = bmin+[(bmax – bmin) 3/4 ], where bmin is the minimum adjustable width, bmax is the maximum adjustable width". This only refers to the positions in which SLCDs will be tested and has nothing to do with the "ideal real life placement".

DMM: "Always ensure that all the cams make contact with the sides of the crack preferably in the middle 1/3rd. of their expansion range (i.e. the cams should be 1/3rd. to 2/3rd. open).

This seems to be just a more conservative approach based on the Wild Country recommendations, althought the Technical Friends and the DMM 4CU have exactly the same cams and the similar sized units have the same expansion range.

And here are my questions:
1. Of course, a SLCD shouldn't be placed fully retracted (or it becomes a bootie) but what do you think it's the reason for the difference between 90% retracted (Black Diamond) and 66.7% (DMM)?
I mean why should I loose 23.3% of the 4CU's working range ?

2. A cam's a cam and a spring acts the same when compressed. Why would a 4CU 66.7% opened still be stable - or a Technical Friend 75% opened - when a BD Camalot at more than 50 % is not ? Is it really safe to place a 2/3rd. open 4CU ?

3. I try not to get my cams stucked or to open them too much, so I usually place them 40% to 90% retracted, but this is based on intuition.
So, what is the REAL working expansion range on your opinion ?

In my opinion, the real working range when, say I am fifteen feet above my last piece on runout Southeastern face, gripped, with my left arm locked of on a slopey edge that my fingers are slowly peeling off of, flagging my right foot with nothing that could be confused with a foothold, with my left big toe crammed into a vertical constriction, and trying to fiddle the first cam that I grabbed into the only horizontal for the next few feet is...over constricted, under constricted, that perfect first placement, four lobes with contact, three, two nothing else will work...if it will hold and eases the tension...whatever.

Now if I am standing on a cooler sized rest, eating a GU, with a fatty handcrack in my face, I'd throw that number 2 Camalot in in favor of say a number one to realize more cam retraction. More is better IMO.

Ben Lyon wrote: More is better IMO.

I agree with this, to a point. I always shoot for 50% cammed if possible.

Ben Lyon wrote:In my opinion, the real working range when, say I am fifteen feet above my last piece on runout Southeastern face, gripped, with my left arm locked of on a slopey edge that my fingers are slowly peeling off of, flagging my right foot with nothing that could be confused with a foothold, with my left big toe crammed into a vertical constriction, and trying to fiddle the first cam that I grabbed into the only horizontal for the next few feet is...over constricted, under constricted, that perfect first placement, four lobes with contact, three, two nothing else will work...if it will hold and eases the tension...whatever.

This is why I carry a #1 and #2 Omega Pacific Link Cam

The basic answer to your first two questions is: it has to do with the camming angle of the lobes. Each manufacturer chooses the camming angle they feel balances range and strength. A #3 Camalot is about ~15 degrees, Friends/DMM use 13.75 degrees, and I couldn't find what Metolius or Trango uses.

As to your third question, I'd say that if I have a choice, I place the cam that is in the upper part of its range (but not "I'm gonna lose this one" range). But there's been a few times where I had no choice but to be in the "I hope this doesn't fall out" range or "my second is gonna hate me" range.

Finally, as for the discrepancy between DMM and Wild Country ranges, even though they have the same lobes, I have no damn clue.

Damn Robert, you guys keep it gansta in the UT! Sick piece.

tooTALLtim wrote:Damn Robert, you guys keep it gansta in the UT! Sick piece.

I love 1911's I have 18 of them :)

verticon wrote:"Ideally, each of the cams should contact the rock at lower to mid expansion range (50% to 90% retracted)". This totally makes sense because the more a cam is retracted, the more the spring will push it against the rock, increasing the friction that holds it in place, thus it's stability.

just to clear something up in case it was not already made clear. The holding force of a cam based on the position of the cam lobes has nothing to do with the spring force, but rather the cam angle. A general concept for cam angle is that with X amount of downward force the cam exerts Y amount of outward force on the crack. The force the cam generates is dependant on its cam angle (angular position of the lobes) which is where the manuf recommendations come from. if a cam is nearly open, the outward force Y per downward force X is much less and therefore the piece is more likely to come out (less friction). The springs are there merely to keep the cam in position. once the cam is weighted the springs can come off with no effect.

There is an optimal range for this angle and is different for each cam, follow manuf recommendations and you will live to buy more cams! aim to get your cams at 50% if possible (I never go more than 75% open). If you have one of each size this should be no problem. unless you've already used the piece that you need! Then place the next best (more retracted is safer). Often times if you make one more small move you can find a placement for a different cam size (unless you are at IC). Seriously though, 66% vs 75% is not worth debating. When you're in the moment there is no way you will be able to tell the difference!

Tyler, you are incorrect.

I don't want to get all wonky engineer style here because frankly I ain't got the time for it. But cam lobes are designed on a logarithmic curve/sprial which yields a constant cam angle regardless of where the cam is in its range.

You are correct that spring tension has nothing to do with holding power, but the guy above talking about spring tension was speaking to tendency to walk, not holding power. and he would be correct that that a cam at the tight end of it's range would have more spring tension. But, it would be so miniscule that in reality it wouldn't make any difference in whether the thing walked or not (unless you had something with absurd spring tension...maybe C3s or something, they seem to have too much spring tension for many people's liking).

If you want the basics of the math involved, including critical angles for cams in outward/downward flares, check out Vaino's page:

vainokodas.com/climbing/cam…

How much of the range of a cam may be safely used depends a lot on the placement. In perfectly parallel cracks, with hard rock, one could safely use a large fraction of the expansion range. In irregular cracks, a cam may be sitting in a nice pod that prevents it from moving around. Conversely, it may be placed so that it can walk to where the crack widens or narrows. In those cases, it's better to be conservative, lest the cam should fall off or get stuck. All this to say that there is no way to specify once and for all what fraction of the expansion range one should use. SLCD manufacturers give guidelines that are to some extent subjective. In any case, it's up to each climber to interpret them according to the situation.

Thanks for your answers.

I wasn't looking for advice on placing cams or for the basics on cams, but for some meaningful opinions on the "useful range" of SLCDs.

I made a graph with the working ranges of my rack and according to different manufacturers' specs, it changes shape from "best rack in the universe" to "drop everything and get a real rack"

The useful ranges in the most plausible graph are varying from 10-25 % to 60-75 % opened, based mainly on intuition and experience with each type of SLCD, but this is way different from the manufacturers' specs and this intrigued me.

Will S wrote:But cam lobes are designed on a logarithmic curve/sprial which yields a constant cam angle regardless of where the cam is in its range.

Ah, interesting. I stand corrected. Guess I should have done a little more research on climbing cam profiles instead of assuming... Now that I think about it that makes a lot of sense. Why would they do it any other way? Thanks for the clarification...

verticon wrote:I wasn't looking for advice on placing cams or for the basics on cams, but for some meaningful opinions on the "useful range" of SLCDs.

These need updating with some of the latest but most of the data still applies:

clydesoles.com/Front/Camsbr…
clydesoles.com/Front/Camssi…
clydesoles.com/Front/Camgra…

Thank you Clyde, the idea of making a "Camgraph" of my rack came to me after I visited your pages and the trouble begun when I started to look for the manufacturers's specs for their cams.

Today I received an answer to my questions from a DMM engineer and I think it might be of some interest to you too:

"Firstly I do find it slightly odd that we talk about 1/3 and 2/3 optimum range. We would, as you suggest be better to align ourselves with Wild Country on this, not only because we use the same cam angle but also the EN Standard requires we test our cams at 1/4 open and 3/4 open, the strength rating we give is based on the test in these two positions. We will look at changing this when we reprint the instructions.

The real expansion range of the cams is from fully retracted to fully open. However there are practical problems that the less experienced user may not have appreciated. As you know if a cam is fully retracted in a crack then it is well nigh impossible to remove. This is because you need to retract the cams from the contact surface to remove them. Also cams have a tendency to walk into cracks. Obviously the experienced user can place a cam in a narrower crack and still get it out.

Similarly as you get towards the fully open position there is a judgment call to make with the rock type that the cam is placed in. If it is very soft rock then as the cam engages the rock it can open significantly further, ultimately to a point where the cam would fail. Again experience is probably the best teacher to the user.

This explains why we are fairly conservative when we talk about 'preferable expansion ranges'. Other manufacturers such as Metolius go a stage further by colour dot marking the sides of the cams to indicate the preferred/optimum expansion ranges.

Other issues that are relevant are the aspect ratios of cams. The aspect ratio is the relationship between axle length and the cam 'height'. On a small camming unit the axle length is far greater than the cam height which makes the cam very stable. On a large camming unit the reverse is true and the cam is less stable. Ideally the optimum scenario is when the axle length is equal to the cam height. Also the aspect ratio changes within the expansion range of a camming unit. It the retracted position its aspect ratio is more stable than when the cam is fully open. When the cam is less stable then there is more of an issue of the cam moving or walking in the crack. This could in certain situations affect the holding power of the cam.

Finally, to add to equation is the cam angle. The greater this is then again you tend to lose stability. DMM use 13.75 degree cam angle. BD use a slightly larger one which helps, along with the twin axle design to increase their expansion range. This instability is more noticeable on larger cams. For the cam angle to work well the spring pressure should be even throughout the opening range as this will give the best fit for cam angle and rock. As I mentioned before rock type is very important. Rough rock engages the cams well, where as smooth rock may not even engage the cams on parallel or marginal placements and the cam may just pull straight out. This is especially problematical on polished limestone and slate.

As you know cams are complex bits of kit and their operation is a skill that is acquired through experience. In our instructions we have to educate the user into the correct operation of the devices in a clear and concise manner and if we err on the side of caution you can perhaps see why. Our instructions are guidelines for use. As it says in the instructions, there is no substitute for instruction by a trained and competent person."

The letter has also a footer:"Any views or opinions are solely those of the author and do not necessarily represent those of DMM Engineering / International Ltd."