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angry
Nov 23, 2008, 1:20 AM
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What would you attribute the failure to?
It seems that camalots do not cause as much outward force as other units thus allowing them to slip right out of the crack in your tests.
I don't know. I know I've taken whippers on identical cams of the same age and they've not budged.
For practical purposes, what sort of force would get put on a cam with a 40 ft fall 100 ft up? That's about the most severe situation I've used mine in.
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basilisk
Nov 23, 2008, 1:43 AM
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Hmm. I just looked at my own gen 2 camalot, and it looks like it has the same peening issue. Makes me wonder if that's intentional. Note the gen 1 camalot doesn't have that issue.
I will say I'm happy they deformed that much. That would only help in real rock. I can't quite tell from the pictures, but would you say the inside lobes deformed more/lost more metal? Maybe lend some credence to the idea that Chouinard used softer aluminum on the inside lobes
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adatesman
Nov 23, 2008, 2:35 AM
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USnavy
Nov 23, 2008, 2:45 AM
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I have two of those .5 and .75 u-stem cams on my rack. If I remember right the .5 is rated for 12 kN and the .75 is 14 kN. That’s what the current ratings are on those sized on the current generation cams are as well.
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adatesman
Nov 23, 2008, 2:51 AM
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USnavy
Nov 23, 2008, 3:21 AM
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Ya this thread is making me wonder if I should trash mine as well.
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adatesman
Nov 23, 2008, 3:28 AM
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USnavy
Nov 23, 2008, 3:52 AM
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Ya well steel here is insanely priced. Those two plates that you have would cost me $1,000 here. Funny for I could get them for $100 back in North Dakota...
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cushman
Nov 23, 2008, 6:13 AM
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Thanks for writing this up! I am glad I retired them, although I hope to never put that much strain on a piece of gear! I am happy that the damage to the lobe of the green Camalot didn't affect it too much, I climbed on it for quite some time after I pried it out of a crack with my nut tool and made that indentation.
Just thinking out loud, when force is applied to the cam and the axle bends, the lobes are not contacting the faux-rock surface with as much surface area - the corners of the lobes are in contact making for less surface area. I wonder if that is the reason why they tracked out. I don't know what that would mean in real rock, though.
Again, thanks for the writeup and the videos!
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adatesman
Nov 23, 2008, 2:39 PM
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USnavy
Nov 23, 2008, 4:06 PM
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Mine comes with an internal batt that lasts 40 hours with the scale on. :) Eh and the approach to the climbing area is the most difficult approach I have ever had to climb so towing up 100 lbs of chain is not an option. lol Maybe 1/4" steel cable though.
(This post was edited by USnavy on Nov 23, 2008, 4:07 PM)
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adatesman
Nov 24, 2008, 6:33 PM
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clintcummins
Nov 25, 2008, 6:00 PM
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What is the coefficient of friction in your test plates?
The camming angle of Friends and other devices like Camalots is chosen based on the friction of likely rock types, including granite and limestone.
If they are used in more slippery rock, such as polished cement, or say polished steel or glass, those are not the specifications in which they were rated by the manufacturer.
I recall an accident where a person thought they would demonstrate the holding power of a Friend in a polished concrete crack on an indoor climbing wall. They jumped off, and the Friend pulled right out.
Other testing rigs I have seen include real rock (such as granite) on the inside of the plates.
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basilisk
Nov 25, 2008, 6:08 PM
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adatesman wrote: Assembly is possible because of a divot in the cam lobe slots that allow the larger diameter on the axle to pass through the lobes.
FINALLY. I always wanted to know what that divot was. Thanks!
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adatesman
Nov 25, 2008, 6:15 PM
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mach2
Nov 25, 2008, 6:39 PM
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Has a surface knurl been considered for the plate surface to help increase the friction between it, and the cam?
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ryanb
Nov 25, 2008, 7:44 PM
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I would need to be convinced that a light cold chiseling offers sufficient texture/changes to the coefficient of friction. It appears that the cam loads are slipping a bit before they hold...this would imply they are catching a on relatively macroscopic texture and not being held by static friction.
You should be able to measure the coefficient of friction experimentally by putting a bit of aluminum on the plate and seeing what angle it starts to slide at (I think the cf is the tangent of this angle?)...like the spadout shoe test but I suggest doing this at least 10-20 times to get an idea of how consistent the cf is across the plate and how it compares to aluminum on rock/aluminum on smooth steal.
Perhaps sanding or chemical etching could offer a better surface.
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dynosore
Nov 25, 2008, 8:00 PM
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Is a slowly increasing load really a fair test for a unit made to catch a sudden, very short duration peak force? I worked in testing labs for years; you always test products and materials under the conditions that they will see in the real world. How long does your test take? Are the cams slipping? It sure appears so.
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MKerr
Nov 25, 2008, 8:46 PM
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I agree with dynosore regarding the test conditions ... quite different results could be obtained with a rapid loading (it would be possible to instrument a drop test for this). Particularly as cam sliding is likely a function of load rate, and this seems to have an effect on the peak force observed.
Regarding the friction, you noted that the aluminum adhered quite strongly to the surface of the steel. I suspect the reason for this is the metals have locally melted (Iron Oxide and Aluminum react exothermically with each other, look up thermite reaction for more detail). This effect also occurs in the rolling of Al sheet with steel rollers (Al has the appearance of sticking to the steel). Not sure how this would effect the coefficient of friction, but certainly adds another wrinkle to the problem.
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adatesman
Nov 25, 2008, 9:18 PM
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adatesman
Nov 25, 2008, 11:14 PM
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hafilax
Nov 25, 2008, 11:34 PM
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The coefficient of friction isn't an issue IMO. The aluminum is deforming and shearing. As the axle bends the edges of the lobes are loaded instead of the flat surface. The pressure increases and the aluminum deforms to have flat spots. The cam can no longer rotate to compensate for the bending and compression and the cam tracks out of the holder.
50% is pretty close to the minimum recommended useful range. I think these tests should be done at more like 75% compressed since that is where I target my placements.
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adatesman
Nov 25, 2008, 11:51 PM
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clintcummins
Nov 26, 2008, 12:06 AM
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Aric,
Thanks for the helpful links to Mal's post on the thread on supertopo, and your additional explanations.
halifax,
Thank you for the explanation of why the aluminum starts shearing. I have to agree that the coefficient of friction is high enough for ultimate load testing.
It would be nice to have an idea of how the rock crumbling affects pullout strength, say with Wingate sandstone vs. some generic granite. I imagine this data has been generated several times in the past, but I don't know if it is easy to find. If it can be found, a summary would be nice. There is the old saying that if you are at Indian Creek and climb with your feet above a TCU, you are "soloing". With a 4-cam unit the load is distributed more, but I'm not sure how much more? (Well enough to hold falls, it seems from videos).
(This post was edited by clintcummins on Nov 26, 2008, 12:09 AM)
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