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1ArmedPullUp
Jan 7, 2008, 9:23 PM
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I've researched this as much as I can and I just have some final questions that I need clarified. I'd really appreciate it if someone wouldn't mind taking the time to practically explain how a cam works to someone with a basic understanding of math and science.
What I basically understand is that a cam takes downward force and converts it into outward force. When you pull on the cable of the cam, it forces the cam lobes out against the surface of the rock, which creates enough friction to hold the downward pull. So here are my specific questions:
What's a log spiral? What's a constant angle? Is the "cam" on a climbing cam the same as a cam in a camshaft (e.g., a device that converts circular movement to reciprocating movement)?
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cracklover
Jan 7, 2008, 9:32 PM
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1ArmedPullUp wrote: What's a log spiral?
The spiral required so that the angle from the point of contact on the outside of the cam to the axle is the same, independent of how expanded the cam is.
In reply to: What's a constant angle?
See above.
Here, read this -> http://web.mit.edu/.../cams/cams.body.html
GO
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1ArmedPullUp
Jan 7, 2008, 9:44 PM
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thanks, great article
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kimgraves
Jan 7, 2008, 10:40 PM
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Another good source for the history and science of how cams work is the Wild Country Cam Book. It's a free PDF or you can order a hard copy.
Best, Kim
(This post was edited by kimgraves on Jan 7, 2008, 10:52 PM)
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1ArmedPullUp
Jan 7, 2008, 11:56 PM
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wow, all these are great, thank you!
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summerprophet
Jan 8, 2008, 12:54 AM
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1ArmedPullUp wrote: What's a log spiral? What's a constant angle? Is the "cam" on a climbing cam the same as a cam in a camshaft (e.g., a device that converts circular movement to reciprocating movement)?
A log spiral is a spiral based on a logarythmic form in which if equally divided, into equal angular parts (ex: dividing a circle into 180 parts of 2degress), will result in the same angle of deflection.
Demonstrated here http://www.uwgb.edu/...ymmetry/log-spir.htm
A camshaft will vary somewhat as the the "camming" part of the camshaft is a small part of the total curve, there are also transitional curves and regular curves invoved. Essentailly, the rollers run along the regular curve while the valve is closed, hit a transitional curve to open the valve, run the spiral to open the valve at a regular rate, and top out on another transition-curve-transition before the valve starts to close.
Complex enough for you?
The mathematics is similar for climbing cams, although the angle of deflection would vary.
An incredibly simplified version of this, and how I explained cams while guiding was this.
"Imagine a wooden wedge being used as a door stop. If the angle of the wedge is too tall, then it will not hold the door in place, but just be pushed along by the door. If the angle is too shallow, then it will stop the door, but become wedged, and will be difficult to remove. If this principle is applied to a curve, then you have the science behind cams."
In climbing there is also a balance between holding power and cam range. The greater the angle, the greater the range, but the weaker the holding power.
(Assuming the same alloy being used for the cams)
(This post was edited by summerprophet on Jan 8, 2008, 12:55 AM)
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onceahardman
Jan 8, 2008, 3:18 AM
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In reply to: "Imagine a wooden wedge being used as a door stop. If the angle of the wedge is too tall, then it will not hold the door in place, but just be pushed along by the door. If the angle is too shallow, then it will stop the door, but become wedged, and will be difficult to remove. If this principle is applied to a curve, then you have the science behind cams."
i like your analogy, but i explained it a little differently...make the ideal doorstop wedge out of rubber. now, wrap the wedge around an axis, and you have a cam.
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curt
Jan 8, 2008, 3:30 AM
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onceahardman wrote: In reply to: "Imagine a wooden wedge being used as a door stop. If the angle of the wedge is too tall, then it will not hold the door in place, but just be pushed along by the door. If the angle is too shallow, then it will stop the door, but become wedged, and will be difficult to remove. If this principle is applied to a curve, then you have the science behind cams." i like your analogy, but i explained it a little differently...make the ideal doorstop wedge out of rubber. now, wrap the wedge around an axis, and you have a cam.
The door stop analogy is a good one. Obviously the same thing applies for stoppers. A nut with a very shallow angle will hold extremely well (and be difficult to remove) in a placement that it fits exactly--whereas a nut with a wider angle will fit a wider range of placements (and be easier to remove) but it will not hold as well.
Curt
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