Why are cam lobes not covered with a high friction coating?

Kyle Tarry wrote: Because the rest of the lobe is anodized (for aesthetic, identification, and corrosion reasons), and it costs more to mask or strip a small section than to just coat the whole thing.

Kyle,
That makes sense.
Been a long time since my materials science class in college, need to refresh my memory on corrosion/anodizing stuff.

john strand wrote:Ray Jardine- "the teeth on cams is purely cosmetic, it doesn't enhance holding power"

He was also wrong about chipping in the Jardine traverae, so...

The no-teeth idea comes from the misconception that the only thing causing camming is normal-force, area-independent friction, so you keep a smooth lobe to ensure a truly constant cam angle through the entire range. Of course, the rock is not smooth either.

Alex R wrote:Darren, it is not about the cams being strong enough. It is about the amount of expansion range you can get while keeping the same strength. Stickier lobes would mean more expansion range without giving up strength.

Well then. Have you considered sport climbing?

Brian Scoggins wrote: He was also wrong about chipping in the Jardine traverae, so... The no-teeth idea comes from the misconception that the only thing causing camming is normal-force, area-independent friction, so you keep a smooth lobe to ensure a truly constant cam angle through the entire range. Of course, the rock is not smooth either.

Nice,,you got it..constant cam angle...thats why Camalots suck,,they try to enhance cam angle..cam angle should be a constant..you can't get more than is there

the caming laws of physics still apply

I'll go with the inventor of the SLCD..there is no misconception here..cams don't need teeth..ever looked at tri cams ?

Teeth actually reduce contanct area..not improve it
Ray's ideas about chipping have zero to do with cams

john strand wrote: Nice,,you got it..constant cam angle...thats why Camalots suck,,they try to enhance cam angle..cam angle should be a constant..you can't get more than is there the caming laws of physics still apply I'll go with the inventor of the SLCD..there is no misconception here..cams don't need teeth..ever looked at tri cams ? Teeth actually reduce contanct area..not improve it Ray's ideas about chipping have zero to do with cams

John,
With all due respect...

I assume the quote ("teeth are cosmetic") you are referring to comes from this article... rayjardine.com/papers/Magaz…

However, notice that even though the article appears on Ray Jardine's website it is not actually written by him, nor is he being quoted in this paragraph...

The metal for the cams was chosen for its properties of frictional adherence and light weight. It's an exotic, aerospace aluminum alloy known as 7075-T6. The teeth in the cams are cosmetic, only. The teeth don't need to grab the rock The holding action is designed to work on pure friction. Regardless of how smooth the granite, limestone, blue ice, or concrete, the cams will hold.

I'm not sure why the author said the "teeth are cosmetic". My guess is he meant to say something like the teeth aren't absolutely necessary, a perfectly smooth cam lobe will work. However, while i am unsure of just how effective the teeth are on a SLCD. I believe the teeth do serve a purpose.

You mention the Tricam as an example of the irrelevance of teeth. However, a Tricam does have a tooth, the fulcrum point. The fulcrum is pointed so that the point can stick into small features of the rock. A Tricam wouldn't work very well if the fulcrum was smooth/rounded. It is actually counter productive to have teeth on the lobes of a Tricam because, unlike a SLCD which rolls against the rock as it cams, a Tricam's lobes slide against the rock. We actually want the lobes to have only a little friction (just enough to prevent it from moving after it has been set), and the fulcrum to have as much friction as possible.

Anything that can be done to improve a SLCD's grip against the rock will improve it's performance. I have a hard time believing that there are no cases in which a toothed cam grips better than a smooth one. Even with my limited experience, I have seen teeth snagging on small features of the rock.

Admittedly, I have very little experience with SLCDs in practice. I only just started leading trad climbs, so I rely mostly on my knowledge of physics in the statements above. I present my opinion only because i find this topic fascinating and i wish to further the discussion. I also realize that you have far more experience than me, and am interested in hearing any contradictory experiences.

cyclestupor wrote: I present my opinion only because i find this topic fascinating and i wish to further the discussion. I also realize that you have far more experience than me, and am interested in hearing any contradictory experiences.

You speak for me also. This is a great thread, and one of the reasons why I find MP so useful. Makes me want all the more to go 'fire in' some cams this weekend...weather permitting!

john strand wrote: Nice,,you got it..constant cam angle...thats why Camalots suck,,they try to enhance cam angle..cam angle should be a constant..you can't get more than is there the caming laws of physics still apply I'll go with the inventor of the SLCD..there is no misconception here..cams don't need teeth..ever looked at tri cams ? Teeth actually reduce contanct area..not improve it Ray's ideas about chipping have zero to do with cams

First, really smart people are still people, and they can be wrong about things. This is why Newton gave up planetary motion (and why it was ultimately solved a century later). My point was that if Jardine said that (and it seems he did not), he was wrong, and he had robust and logical reasons to be wrong elsewhere too.
Second, cam angle is not the only design parameter, otherwise we would've abandoned toothed cams long ago. They add quite a bit in terms of manufacturing and QA/QC complexity. On gritty, sandy rock, though, teeth become pretty important. Without teeth, it takes a lot less sand to cause that ball-bearing cam-slide thing we all dread on dirty climbs.

As was stated above, tricams use the same geometrical realities as cams, but their actual operation is quite different, so their design needs will be quite different. Your statement re:smooth lobes on cam heads is like saying that tricams don't need curved faces, since hexes also cam, and they have flat faces.

john strand wrote: Nice,,you got it..constant cam angle...thats why Camalots suck,,they try to enhance cam angle..cam angle should be a constant..you can't get more than is there the caming laws of physics still apply

Camalots have a logarithmic spiral-shaped cam and so have constant cam angle. They chose a different constant cam angle than Jardine did originally. I don't know what exactly constitutes "the camming laws of physics," but cam angle calculations are based on holding power considerations that are formulated in terms of Amonton's friction laws, which probably don't hold for cams. It is those calculations I suggested implied a certain amount of "doublethink" in the cam design process.

john strand wrote: I'll go with the inventor of the SLCD..there is no misconception here..cams don't need teeth.

Of course cams don't need teeth---that's a straw man. The question is whether teeth improve performance. I can think of arguments on both sides of the question---but what is needed would be testing showing that the teeth help in at least some circumstances and don't generally decrease performance. Ray Jardine's opinion is interesting but not, in this case, authoritative. And by the way, I don't think Jardine invented the SLCD...

DMM say their elaborate grooving and the widening of the cams increases holding power (presumably as compared to their former models). If they can back this up with data, we'd have some evidence that surface treatments help.

john strand wrote:...ever looked at tri cams

Does anyone know if a toothed, grooved, or knurled version of tricam might hold better? And by the way, although I haven't done any computations, I don't think tricams are logarithmic spirals and if so, they don't have a constant cammming angle.

rgold wrote:I don't know what exactly constitutes "the camming laws of physics," but cam angle calculations are based on holding power considerations that are formulated in terms of Amonton's friction laws, which probably don't hold for cams. It is those calculations I suggested implied a certain amount of "doublethink" in the cam design process.

I think the use of the word doublethink is a bit unfair. Even if Amonton's friction laws aren't precisely accurate for this circumstance they still are the dominant description of behaviour.

AKA you are going to get consistent friction for consistent normal force. So sticking a constant camming angle then you are going to get almost identical results about the range. (The only possible other affect would be the difference in lobe stiffness about the range, but I doubt that affects much.)

Teeth really are unlikely to have any affect unless the rock is course to give direct mechanical engagement. Or that the rock is soft and can dig in.