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adatesman
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Nov 22, 2008, 5:05 PM
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Hey Folks, looks like its your lucky day! We've got a 2-for-1 special on cam destruction today, so you're in for a treat. Thanks to Cushman, we have a pair of old-school U-Stem Camalots (Purple #0.5 and Green #0.75) for destruction. They're both ~1998 vintage and were recently retired from his rack. Well, recently as of of when he sent them, which was a while ago. Anyway, they failed in very similar manners so I figured I'd combine it all into one ginormous writeup.....
First up, the Purple. It is (was) in fairly good shape for its age and the action is (was) still good. (BTW, click on the pics for a supersized version)
I don't have any listing of what the U-Stem Camalots were rated to {EDIT- Duh, its on the tag on the sling.... They're both rated 12kN}, so can't really say how well the Purple did. The peak load held was 2391 pounds-force (10.64kN), but if you watch the video (Link) you'll see why I'm not so thrilled with how it did. In a nutshell, the axles bent severely and the lobes tracked right out of the fixture.
Here's the chart of the forces:
Not too confidence inspiring, is it? The small, regular dips are from the leaky seals on my pump, but a good bit of this is from the cam yielding and pulling out of the fixture. Speaking of which, this is what it did to the fixture plates:
Those streaks are aluminum from the cam lobes that is completely embedded into the texture of the plates. No amount of scrubbing with a wire wheel could get it out, so I had to re-texture over it with a hammer and cold chisel. Fortunately this managed to break most of it free, so the plates don't need to be resurfaced and re-textured again.
Anyway, here are the post-test pics. This side doesn't look so bad except for the flat spot on the inner lobe. Also take note of the small peening on the end of the left axle; we'll be revisiting it in a moment.
This side isn't looking so good. Remember the small peen on the axle? The axle on this side had a similarly small peen and it pulled through the end plate. You can hear this happen in the video and immediately after it is when the forces dropped significantly and the cam pulled out. You can also see the flat spot on the inner lobe, marked with the arrow.
Here's an end shot to show how tweaked the axles got:
Remember the streaks on the plates? Here's where they came from.
Oy.
At this point you're probably thinking that the Green surely had to have done better, right?
Sadly, no.
In fact, the Green is the reason its taken me so long to break these two.... Shortly after receiving them I gave it a try and started with the Green one. No dice. It just kept slipping out of the fixture. After a bunch of attempts (Video of Attempt 1 {EDIT- Sorry, looks like the only copy of that video I have is Flash and YouTube can't import it}, Attempt 2 and Attempt 3) I finally gave up and put them away for a while. On an unrelated note, its been a long time since I looked at these and I'm amazed at how much better my videos have gotten. Woo-hoo, as they say.
Anyway, here's a chart of the forces for those three tests. Notice how it catches again after slipping:
And its not just that it would slip.... It would do all sorts of screwy things too, like this:
And this:
Which left nice flat spots on the lobes, similar to what happened with the Purple above:
This then brings us up to the other day when I finally gave it yet another try. Here's how the cam looked then:
This time the cam held well enough to mangle it, but it still didn't do very well and failed at peak of 2058 pounds-force (9.15kN). Just like the purple one, the axles bent and then it slowly pulled out of the fixture. Here's the video: Link
And a chart of the forces:
Just like the Purple one, the Green also had axles that were insufficiently peened to prevent the end plate from popping off. In this pic, not only can we see the flat spot on the inner lobe but there's puckering of the end plate around the small peen as well.
And here the end plate completely popped off and we see some damage from a nut tool long ago when Cushman was trying to get it unstuck from a crack somewhere. 
Here's an end shot to show how much the axles bent:
And a pair of shots on what happened to the lobes. Yup, looks like I'm going to have to re-texture the fixture plates again. Ugh. It might be time for me to build a fly cutter and just do this on the milling machine.
I'm not about to tell anyone where to draw the line on what is and isn't safe gear-wise, but I will say I'm not too thrilled with how these two did in the tests (especially the Green one) and am happy that Cushman decided to retire them.
On an loosely related note, while going through my old files looking for the video of the original tests of the Green Camalot I finally found the video of the destruction of the Blue #3 pre-C4 Camalot that Cushman sent. Looks like I have another write-up to do.... Although it won't be tonight though, so don't wait up for it. I'm a bit burned out from doing two of them today and its long past Beer:30. 
-a.
(This post was edited by adatesman on Nov 24, 2008, 3:41 PM)
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angry
Nov 22, 2008, 5:20 PM
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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 22, 2008, 5:43 PM
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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
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Nov 22, 2008, 6:19 PM
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Hey Angry,
Guess I'm not the only one in on a Saturday night, huh? What's your excuse? 
To be honest, I don't know there's any single thing I can point to as the reason for the funny behavior and lower than expected failure. It seems to me to be a combination of things....
- The axles on both U-stem ones are .163" diameter, which is much smaller than the .217" of a current #0.5 C4 (I don't have a #0.75 handy, so can't measure it for comparison). Assuming they used similar material for the axles, the old ones would be much weaker.
- The axles on the U-stem ones are not supported in the middle as they are in C4s (they're supported between the lobe pairs instead), which means there's more leverage on the center of the axle when the cam is loaded.
- This leverage is compounded by the fact that the axles are longer than on C4s.... they look like they were roughly 2" on the old ones (they're bent now and hard to measure) and 1.675" on a 0.5 C4
- The lobes are thinner on the old ones (0.185" compared to the 0.250" on the 0.5 C4), which means there's less material in contact with the fixture.
In comparison, I had no trouble with the single stem #3 pre-C4 that Cushman also sent pulling out of the fixture, so I don't think its simply a matter of the fixture not being able to handle BD's cam spiral. Plus I had no trouble with breaking a Red Alien, which uses an even larger spiral.
As for your scenario, I assume you mean pro at 100 feet, climb 20 feet above it then fall 40 feet (ignoring rope stretch)? Using an 80kg climber and a 10.2mm rope, Petzl's Fall Simulator says that it works out to a fall factor of 0.333 and puts a force on the gear of 5kN when using a Reverso and 5.96kN using a Gri-Gri. That's well below what the cams failed at the other day, but rather close to the results I got with the Green one the first couple times. So maybe its a crap shoot and highly dependent on the lobes sticking behind features in the rock? My test fixture is close to a worst case scenario, since it makes the cam rely almost entirely on friction to stay in place since the plates are parallel and have only enough texture to get the cam to stick.
Also don't forget that the Green one failed the first round of tests without bending the axles.... And in each of the tests it slipped and re-caught a bit further down. Perhaps the ones you fell on actually did slip a bit and re-catch? Unless you're looking specifically for it you might not notice.
-a.
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adatesman
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Nov 22, 2008, 6:35 PM
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basilisk wrote: 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.
Interesting.... No one's donated a Gen 1 Camalot for testing yet, so I'm curious if it would also have the problem with the end plate popping.... Hint Hint... 
basilisk wrote: 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?
Well, they deformed differently... The inner ones stayed mostly perpendicular to the fixture, so the wear on them was fairly well distributed across the face of the lobes. Because of the bend in the axles the outer lobes wore on the edge of the lobe face and it barely reaches halfway across on either of them. Looking at what was left stuck in the texture on the plates it seems like the lobes all lost roughly the same amount of material.
basilisk wrote: Maybe lend some credence to the idea that Chouinard used softer aluminum on the inside lobes
I dunno. I will say that the guy I sent a bunch of lobes to for hardness testing says this is not the case, but I don't know if he actually tested it. Here's his post on the subject over in the Cam Lobe Hardness thread, so you may want to ask over there (he's quite busy, but following the thread as he finds time). Actually, due to a problem with the post office, I ended up sending him both an inner and outer lobe from a #3 pre-C4 Camalot, so maybe the test results I posted had samples from each of the two lobes.....
Oh, and I neglected to mention above that all the pics are thumbnails linked to large versions of the pictures. The amount of wear on the lobes is easier to see in the supersize version.
-a.
(This post was edited by adatesman on Nov 22, 2008, 6:37 PM)
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USnavy
Nov 22, 2008, 6:45 PM
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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
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Nov 22, 2008, 6:51 PM
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I guess it appears that they both broke under spec! Oh Noez!!!!!
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USnavy
Nov 22, 2008, 7:21 PM
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Ya this thread is making me wonder if I should trash mine as well.
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adatesman
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Nov 22, 2008, 7:28 PM
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Seems to me you recently built a pull tester and could find something more interesting to do with them than throw them in the trash....
I hear ya though.... I found these results rather unsettling.
-a.
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USnavy
Nov 22, 2008, 7:52 PM
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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 22, 2008, 10:13 PM
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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
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Nov 23, 2008, 6:30 AM
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A couple more thoughts while I wait for my coffee.... (MMmmm..... fresh home-roasted French press coffee..... )
- The fixture was set for both cams such that they were at about 50% expansion. The axles bent to the point that both cams were tipped out at the time of failure.
- In the original set of tests the Green one was also set for roughly 50% and the axles somehow didn't get deformed during its multiple failed tests
- I'm an idiot..... Both cams have the rating listed on the tag sewn to the sling.
 They're both rated 12kN.
- Upon closer inspection, it looks like the axles actually aren't identical.... The one that the inner lobes are on is much larger in the section between the inner lobes, measuring 0.246".
- Similarly the axle the outer lobes are on are on are larger at the ends, coming in at 0.244"
- The slots in the cam lobes are somewhere around 0.185", so I'm a bit curious how they managed to assemble them (can't slide a 0.246" axle through a 0.185" slot...). Must be bushings on the ends of the outer lobe axle.
- I'll see about taking one of them apart later today and getting some pics.....
-a.
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adatesman
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Nov 23, 2008, 6:39 AM
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USnavy wrote: 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...
Actually, I was thinking more along the lines of some real-world testing.... My gear is AC only, so dragging it out to the crag to try an actual placement isn't so easy. A lot of the scales I've seen like yours can run off batteries, so if your is like that as well it wouldn't be so hard to find a ground level placement and then hook the pullback ram to a tree with some chain.
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USnavy
Nov 23, 2008, 8:06 AM
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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, 8:07 AM)
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adatesman
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Nov 24, 2008, 10:33 AM
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Well, I took the Green apart last night and found some interesting things....
First off, the axles are far from identical and there are no bushings on them. The large sections of the axles measured 0.2475" diameter and matched the hole the lobes rotated on. The small sections of the axles measured 0.1665" diameter. This would explain the difference in the size of the peening on the end plate, since the diameter being peened was significantly different. (click pics for supersize)
The heads have two .250" diameter holes in them and fit over the large sections of both axles. I gave this one a good brushing with a wire wheel to clean it up for the pics and the brazes look really well done. There's also evidence of a weep hole in the head for the braze, like Trango does with their Ballnutz. The cable is 1x19 construction and 0.131" diameter, which might be 1/8" nominal. The individual strands are 0.025". Oh, and I cut the head off to count the strands.... it didn't fail in the testing.
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.
Also of note is that the slot is actually considerably larger than the small diameter of the axle and measures 0.189" (and I'm not talking about the section with the divot).
I would not go so far as to say this is a design flaw, but it certainly contributed to the bending/failure (more on this in a minute) and is something they improved upon greatly with the single-stem pre-C4 model. For comparison, here are the axles from Cushman's #3 pre-C4 (report coming in the next couple days). Notice how they're the same diameter (0.248") and one is reasonably straight while the other is rather bent, rather than both axles bending like on the U-stem unit. And just FYI, the bent axle is actually straighter than it had been... It took a 24oz hammer to get the axles out of the head (I didn't want to cut it off) and the cam failed in passive mode at a peak of 4298 pounds-force (19.12kN) after having the sling fail during two earlier tests at different amounts of expansion (16.94kN and 15.65kN, and the axles remained undamaged).
On the pre-C4 model, the opposite axle actually rides slightly inside of the arc cut in the cam lobe (sorry, no pic). This allows the opposite axle to bear directly on the cam lobe and share in holding the force. You can clearly see evidence of this on the lobe from the #3.
Due to the gap between the slot and cam lobe on the U-step units, this doesn't appear to happen and there is no evidence of deformation around the slot. Deformation is clearly visible on the edge of the cam lobe though.
So my theory is that the gap in the slot allowed the axles to begin to deform, which in turn caused the lobes to continue to rotate towards tipping out, at which point the lobes rotated to the point the divot came into play, which prevented the lobes from applying their usual amount of outward force and the cam slipping from the fixture. The failure of the cam in the last test was possible due to increased friction in the test fixture due to my having re-textured it several times since the original tests.
Thoughts/comments?
-a.
(This post was edited by adatesman on Jan 12, 2009, 7:34 AM)
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clintcummins
Nov 25, 2008, 10:00 AM
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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, 10:08 AM
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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
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Nov 25, 2008, 10:15 AM
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clintcummins wrote: 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. {snip} Other testing rigs I have seen include real rock (such as granite) on the inside of the plates.
There's a good thread somewhere (I don't recall if its here or on Supertopo) about this. I'll find it and post a link.
In the meantime, if I recall correctly consensus was that lightly textured steel was the preferred material for the fixture. Mal @ Trango chimed in that while rock worked well, it didn't hold up well and was only good for a handful of pulls before it crumbled.
Also, I think the UIAA test fixture for certification is steel as well....
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mach2
Nov 25, 2008, 10:39 AM
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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, 11:44 AM
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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, 12:00 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, 12:46 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
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Nov 25, 2008, 1:18 PM
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I found some of the links I was looking for, but not all....
First, here's a link to the Mal's post on Supertopo where the discussion turns to using rock in the test fixture for cams.
Second, here's a pic of the last page of UIAA Cert 125 (PDF Warning!). I know I read somewhere that the fixture is textured steel, but damned if I can remember where it was. The pic here does make it look like a textured metal surface though.
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adatesman
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Nov 25, 2008, 3:14 PM
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Ok, I give up. I can't find the copy of EN 12276 that I had found online a while ago and finally ponied up the money to buy a copy. Fortunately its $100 less than it was last time I looked (I can justify spending $30 for 12 pages of mostly boilerplate documentation, but not $130....), so I now actually have a copy to reference when needed.
Anyway, here are the pertinent sections to put the discussion regarding slow pull vs drop test to rest. This is simply how cams are tested for certification, and while I/we may not agree with it that's just how it is. When constructing my puller I tried to conform to the certification test as best I could while staying on a limited budget. I think I came fairly close, but am open for discussion about the implementation of it. Discussion regarding slow pull vs drop test will need to go into another thread (not to imply I'm against having the discussion, its just a separate topic).
Sadly the document is copyrighted, licensed and watermarked, so I'm afraid I can't just post it.... 
In reply to: {words, words, words.....} 3. Definitions 3.3 holding force: The force necessary to cause the frictional anchor to break or slip through the test apparatus, as determined in the strength test in accordance with 5.4.2. {more words....} 4.2 Strength When tested in accordance with 5.4.2, the holding force shall be at least 5.0kN. {still more words.....} 5.2 Apparatus for strength test 5.2.1 Layout The apparatus consists of two parallel, rigid steel supporting jaws..... {more words, mostly about the connector for pulling the gear} The static friction between the supporting jaws and the frictional anchor shall be great enough to prevent the frictional anchor from slipping through at the test load, but the maximal surface roughness shall not exceed 500um. {again, more words....} {pics similar to UIAA Cert 125 above....} 5.4.2 Strength 5.4.2.1 Rate of loading - of 20mm to 50mm per minute if the frictional anchor does not contain textile elements - of 50mm to 200mm per minute if the frictional anchor contains a textile element, subjected to stress during the test. {words...} 5.4.2.3 Apply a load to each frictional anchor until it breaks or until it is pulled out of the apparatus.
I think I covered the fabrication of my test jig over in the How to Build a Test Rig thread, but maybe not.... Anyway, mine is a pair of 1" thick 1018 steel plates with holes in the corners for 3/4" threaded rod to pass through for adjustability. I originally went with a sanded finish from a 60 grit sanding disk on grinder, but that proved too fine a finish and I couldn't get cams to stick. So I bit the bullet and proceeded to spend several hours with a sharp cold chisel lightly texturing it by hand. Doing it sucked big time, but it works well now. You can see the results by clicking on the image of the plates above for the large version of the pic.
As for there being enough friction between the cam lobes and the plates, per Viano Kodas' website in order for a cam to hold in a parallel crack the coefficient of friction has to be equal or greater than the ArcTan of the tangent angle. So with a coefficient of friction for aluminum on steel of ~.45, this works out to a maximum cam angle of ~27.7 degree (assuming I did the math right...)
And as for the aluminum smeared on the plates, it was more of a mechanical bond from the aluminum shearing off into the nooks and crannies on the plate than anything else (like when a file gets loaded up when filing aluminum or zinc).
-a.
(This post was edited by adatesman on Nov 25, 2008, 3:22 PM)
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