Overcamming -vs- Undercamming

[EWolfe]

I have a partner I have climbed with for years who invariably overcams his placements. He also sets them deep, making following a bitch. I tend to place shallow and undercam, making it easier for the follower, but he complains my placements are insecure.

My question: Does overcamming and burying make you feel more secure? Or am I being too loose and shallow with my cam placements (granite/ NW)

[layton]

you have the loosest slots in town

kill your partner for being a sissy

[Peter_Puget]

Wow E I was thinking that yesterday while cleaning a pitch. I think somehwere in the middle is where you should aim for but it's hard to fight the impulse to really stick on in, so I confess to sometimes sticking it in too far. My partner claimed she was placing her cams that way because she didn't have enough slings and wanted to reduce the chance rope drag would mess up the placement. Not sure if I am convinced but in same cases that seems like a good point.

 

PP

[billcoe]

Word to the wise make sure you are using HIS cams. Should reduce friction between you as his will invaritably be getting stuck and left due to his placements.

 

Bill

[Jens]

Depends on the brand. The metolius cams walk tons with very little pressure so I sometimes error on the overcam side when I am using em'.

[EWolfe]

An additional note: I am not talking about the cam being "tipped out" here, just in the halfway to 3/4 range.

I have seen it a lot: people tend to think if the cam is not stuffed into the crack like a wedge it is not secure.

I believe the opposite is true: if a SLCD is overcammed, it has more tendancy to "pop" out because the lobes are not loaded within acceptable range

[layton]

I stuffed it in too far once, and it was immediately pulled out.

[Sphinx]

MisterE said:

An additional note: I am not talking about the cam being "tipped out" here, just in the halfway to 3/4 range.

I have seen it a lot: people tend to think if the cam is not stuffed into the crack like a wedge it is not secure.

I believe the opposite is true: if a SLCD is overcammed, it has more tendancy to "pop" out because the lobes are not loaded within acceptable range

This sentiment is false. The design of a cam means that the low end of its 'acceptable range' is as small as you can retract the thing. There is no physical reason for a cam not to work as a cam when 'overcammed'. I don't know why people keep spouting that cams work like nuts when they are overcammed. They don't. The same physics is at work. How can it 'pop' when all lobes are contacting the rock and acting normally? The only problem with an overcammed piece is that it is difficult to remove. The strength of the placement CANNOT be compromised, according to Newton and the rest of those geeks.

 

Personally, I like a cam that is reasonably deep, but still easily removed, with the lobes retracted between 1/2 and 3/4 of its range.

 

We should get rid of the 'cam as a nut' argument, it is nonsensical.

[texplorer]

Sphinx you are only partially correct. The curvature of the cam lobes provides different holding power at different angles. At the proper camming range the lobes press outward but as you move away from that range the angle of force on the rock will change slightly. When cams are severaly overcammed they have less holding power and a quick jerk can dislodge them before the springs in the cam have time to react.

 

One side not- Metolious this next year is going to start putting dots on their cam lobes so newbies and those of you that have never learned will know when a cam is properly placed.

[catbirdseat]

I have to agree with Sphinx. The lobes are designed so that the "camming angle" is the same thoughout their range (what is it? 13.5 degrees). Thus the force exerted by the lobes is the same. To the extent that the springs obey Hooke's law, the force prior to a fall is greater the more the lobes are retracted.

 

I have noticed that the majority of fixed cams I have seen are Metolius. Whether this is because more people use them or they walk more is up for debate. If popularity was any measure, you would expect to see lots of Camalots as fixed pieces.

[Sphinx]

I might be wrong, but I thought the entire principle behind cams is that the angle between the cam lobe and the rock is constant through the entire expansion range. If what the manufacturers say is true, then the cam angle is constant (it is physically possible), and the cam will have the same holding power no matter how much it's retracted. If I am wrong, then the cam manufacturers could improve their cams by using the correct shape. Wild Country says that they use a constant cam angle of 13.75 degrees, and they mention nothing about it changing depending on the degree of retraction. Do you have verification of your theory Tex? I'd love to see it.

[Sphinx]

Metolius cams are very easy to fix, I'm not sure why. But in my experience, I have struggled with Metolius cams much more than with Camalots.

[texplorer]

Sphinx,

I don't have any hard evidence but I do know that not all cams have the same lobes. I believe this is due to wild country patenting the shape of their cams. I could be wrong on that though.

[Sphinx]

No, the function that determines the shape of the cams is the same for all cams. The only thing that changes between companies is the cam angle. But as far as I know, all cams have a constant cam angle, giving each one ONE strength.

[Paul_detrick]

THIS IS A GOOD TOPIC, MY CLIMBING PARNER DOES THE SAME(OVERCAM) AND I TEND TO TRY AND LET THE CAM OPEN A BIT(I LIKE HALF WAY). I LIKE TO USE LONG SLINGS WHICH SEEMS TO HELP.

[Bug]

I do not know the angles or any other theoretical stuff, but I do know that I have fallen on friends, Camelots and TCU's at all degrees of placement and have not had one pull. Maybe this is luck. I don't know. But, I do know that I have fixed one friend and have seen many fixed cams. I try to place them 1/2 to 3/4 also and I always put at least a short draw on them. It seems like they do like to walk more the less retracted they are. One more note, I have seen friends hold a fall on two cams. Any placement is better than no placement. You might be pleasantly surprised.

[catbirdseat]

I would be interested to see the cam spring force diagram for various cams. That is, how much outward force the cam lobes exert on the walls of the placement versus % cam lobe retraction. It might go a long way towards explaining why some cams walk and others don't.

[Necronomicon]

Got this from John Middendorf's webpage.

 

Logarithmic Spirals

 

The modern camming unit utilizes the logarithmic spiral (also known as an equiangular spiral). The logarithmic spiral is a mathematical curve which has the unique property of maintaining a constant angle between the radius and the tangent to the curve at any point on the curve (figure 1).

 

A logarithmic spiral cam (a "constant angle cam") ensures that the line between the axle and the point of contact (the "line of force") is at a constant angle to the abutting surface, independent of how the cam is oriented. Thus the force diagram for a given camming unit will be identical no matter how it is positioned in a crack, i.e. whether it be compressed or expanded (figure 2).

 

God has spoken. Take note, Tex.

[Greg_W]

Another note, from John Long's book, is that if you stuff a cam way back into a crack, it is more difficult to truly see how the lobes are contacting the rock. Better to place the cam near the edge of the crack so you can see how everything is setting against the rock. As far as over- and under-cammed placements, I go for optimal and get the best I can.

 

Greg_W

[Sphinx]

Necronomicon said:

Got this from John Middendorf's webpage.

 

Logarithmic Spirals

 

The modern camming unit utilizes the logarithmic spiral (also known as an equiangular spiral). The logarithmic spiral is a mathematical curve which has the unique property of maintaining a constant angle between the radius and the tangent to the curve at any point on the curve (figure 1).

 

A logarithmic spiral cam (a "constant angle cam") ensures that the line between the axle and the point of contact (the "line of force") is at a constant angle to the abutting surface, independent of how the cam is oriented. Thus the force diagram for a given camming unit will be identical no matter how it is positioned in a crack, i.e. whether it be compressed or expanded (figure 2).

 

God has spoken. Take note, Tex.

SEE!

[wrench]

slightly different way of looking at it: w.c. explains the angle as being a compromise b/w stability and force. w.c.'s 13.75-deg angle is sort of the benchmark that other manufacturer's use. the smaller the angle, the greater the outward force the lobes apply to the rock. the large the angle, the greater the stability of the lobes in the rock. metolius uses a slightly smaller angle (according to their web-site), which then makes them apply more outward force to the rock (stronger fall-holding potential), but makes them a little less stable, which should explain why they walk more. w.c. uses the analogy of a ladder -- the steeper you lean it against the wall, the less force against the wall but more stability, while the shallower you lean it, the more force against the wall but less stability.

 

re: depth of placement, one other potential pitfall of smaller angles and thus more outward force applied to the rock is that the cams could theoretically pulverise the rock, in which case a shallow placement could track out of the crack. so the quality of the rock should be another consideration in deciding how deep to place your pieces.

 

in any case, it is true (for the 20th time in this thread) that all cams are designed with a 'constant cam angle,' so the force the cams put on the rock is the same within most of the range of the cams expansion.

[wrench]

'scuse me, just double-checked my statments w/ w.c.'s cam book online:

http://www.wildcountry.co.uk/pdfs/cam_book/Wild_Country_Cam_Book_2Mb.pdf

 

looks like i was wrong in that the larger the cam angle, the greater the expansion range, not "the greater the stability." tendency to walk is more of a function of type of spring used and overall head-width of the cam. so size of angle is function for determining amount of outward-force vs. expansion range.

 

see also more interesting info from metolius:

http://www.metoliusclimbing.com/camshome.htm#holding power

 

blah blah blah i'll shut up now.

[Dru]

you never have to worry bout this with hexes and nutz

[atomic]

I heard recently that the latest authority on this subject suggests that the optimal range is 50% to 75% (rather than 50%).

 

Don't have a source to quote, though. I heard it by word of (reliable) mouth. Might be from BD?

[Coopah]

Or just don't fall