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Does water in a crack effect a cam's holding power

Andy Novak · · Bailey, CO · Joined Aug 2007 · Points: 370

I cant believe I just read every post in this thread. Excuse me while I go shoot myself in the face.

Josh Olson · · Durango, CO · Joined Mar 2010 · Points: 255

Doesn't a cam rely on friction for the initial force, but only the initial force? I thought the cam's whole design was to create a lot of force outward, which wouldn't be friction, it would be the force pulling down translated from the y direction to the x direction. I know I should be able to phrase this a whole lot better, but I think if the cam held for the initial jerk, it would be safe. I know this doesn't have much to do with the op, but it got me thinking...

Cota · · Bend OR · Joined Dec 2008 · Points: 0
Josh Olson wrote:Doesn't a cam rely on friction for the initial force, but only the initial force? I thought the cam's whole design was to create a lot of force outward, which wouldn't be friction, it would be the force pulling down translated from the y direction to the x direction. I know I should be able to phrase this a whole lot better, but I think if the cam held for the initial jerk, it would be safe. I know this doesn't have much to do with the op, but it got me thinking...

Actually it relies on friction the whole time just because it has an outward force does not negate the friction. Just think if the spring was much stronger or weaker, friction would still be what keeps it in place.
Cota · · Bend OR · Joined Dec 2008 · Points: 0
Josh Olson wrote:Doesn't a cam rely on friction for the initial force, but only the initial force? I thought the cam's whole design was to create a lot of force outward, which wouldn't be friction, it would be the force pulling down translated from the y direction to the x direction. I know I should be able to phrase this a whole lot better, but I think if the cam held for the initial jerk, it would be safe. I know this doesn't have much to do with the op, but it got me thinking...

Actually it relies on friction the whole time just because it has an outward force does not negate the friction. Just think if the spring was much stronger or weaker, friction would still be what keeps it in place.
Josh Olson · · Durango, CO · Joined Mar 2010 · Points: 255

But if a spring breaks, the cam will still hold, won't it?

Josh Olson · · Durango, CO · Joined Mar 2010 · Points: 255

I know what I'm getting at! The spring in a cam creates the initial friction, then the downward force creates the friction to catch the fall. The spring alone isn't strong enough. Sorry for the sidetrack!

redlude97 · · Unknown Hometown · Joined Jun 2010 · Points: 5

Friction is the result of the normal force and the coefficient of friction between the cam and the rock. Water decreases the coefficient of friction and thus the resulting friction for the same normal force(outward camming action)

Eric Krantz · · Black Hills · Joined Feb 2004 · Points: 420
Josh Olson wrote:Doesn't a cam rely on friction for the initial force, but only the initial force? I thought the cam's whole design was to create a lot of force outward, which wouldn't be friction, it would be the force pulling down translated from the y direction to the x direction. I know I should be able to phrase this a whole lot better, but I think if the cam held for the initial jerk, it would be safe. I know this doesn't have much to do with the op, but it got me thinking...
If there's a force pulling down there's got to be a force pulling up otherwise the whole system accelerates. The force pulling up is friction. The large outward force produces a large frictional force preventing the cam from slipping - the larger the outward force the larger the frictional force. Water is a lubricant that reduces what physicists and engineers call the "coefficient of friction", thus reducing the frictional force that keeps it from slipping. If the force of the downward pull becomes greater than that of friction, it will slip. Sometimes dry is good.
yak · · Unknown Hometown · Joined May 2010 · Points: 0
Josh Olson wrote:But if a spring breaks, the cam will still hold, won't it?
Gosh, you people... always coming up with the craziest scenarios...

If a spring broke I suspect it would definitely affect the placement. It might even effect slippage. So, don't go plugging cams into those cracks with running water behind them, mmkay?
coppolillo · · Unknown Hometown · Joined Sep 2009 · Points: 70

Andy Novak receives the sanity award for this thread.

Geir www.ToofastTopos.com · · Tucson/DMR · Joined Jun 2006 · Points: 2,751
Mike Anderson wrote:For those randomly seeking life and death advice on the internet, please take note that we have received two completely contradictory answers delivered with equal authority and confidence.
right on mike!
Greg D · · Here · Joined Apr 2006 · Points: 883
Phil Lauffen wrote:wow? an ME in the house? I guess engineers are still notoriously bad at grammar/spelling. You all realize there are two definitions to effect: 1)something that is produced by an agency or cause; result; consequence: Exposure to the sun had the effect of toughening his skin. 2)power to produce results; efficacy; force; validity; influence: His protest had no effect.
Wow. Someone that can cut an paste definitions. And you must be an... or is it a...

Take it easy Phil. He was just trying to help.
Greg D · · Here · Joined Apr 2006 · Points: 883

Some weird replies here. Some jokes, some sincere.

Cams 101.

1 the cam's spring is there to hold the cam in place and has negligible effect (or is it affect) on the cams holding power.

2 cams critically rely on friction. a downward force is converted to an outward force increasing the friction between rock and cam lobe.

3 any lube, such as water, baby oil, sun screen and ky jelly, decreasing friction between rock and lobe will decrease a cam's holding power.

4 ky jelly is very slippery but water soluble. so if you have ky jelly on your lobes, adding water (or rain) may improve your friction and your love life.

Buff Johnson · · Unknown Hometown · Joined Dec 2005 · Points: 1,145

yeah, not quite so sure improving the friction helps.

Wiled Horse · · Unknown Hometown · Joined Dec 2002 · Points: 3,669
Josh Olson wrote:But if a spring breaks, the cam will still hold, won't it?
unless there is no one around to hear it.

or they might be in Camcun.
Ray Lovestead · · Boulder, CO · Joined Jan 2008 · Points: 108

I've been thinking of reducing weight on my rack by removing the springs on the cams. Is this a good idea? How will this effect the performance. Will Yak please respond?

Tim Pegg · · Unknown Hometown · Joined Dec 2009 · Points: 5
kennoyce wrote: In your reply you stated, "No, water does not effect a cam's holding power." Now I'm assuming that you meant to say water does not affect a cam's holding power. If this is the case than you would be wrong...
Tee-hee.
Phil Lauffen · · Innsbruck, AT · Joined Jun 2008 · Points: 3,098
Greg D wrote: Wow. Someone that can cut an paste definitions. And you must be an... or is it a... Take it easy Phil. He was just trying to help.
I don't 'take it easy' when someone says:

kennoyce wrote: By reading his statement, even a second grader would be able to tell that he has absolutly no clue what he is talking about and doesn't even understand the OP's question, so really there is only one coherent answer given in this thread.
I see that as just being a jackass. And for the record I'm an engineer also so I don't do grammar that good.

I'm sorry Kennoyce if I offended you.
Guideline #1: Don't be a jerk.

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