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C4 with kinked stem: still safe?

Aric Datesman · · Unknown Hometown · Joined Sep 2008 · Points: 145

@Abram- Don't want to drift the thread too much, but in a nutshell there is enough clearance between the axles and the arc cut into the opposing lobes that when loaded the axles begin to bend and the outward force is reduced. This problem is compounded if the lobes are expanded enough to reach the divot cut into the axle clearance arc, which allows the axles to bend significantly and pull out well under rating. The one in the pics below took 4 attempts to get it to stick in the test fixture on account of the bending allowing individual lobes to slip and twist the cam into all sorts of uneven placements, and when I finally got it to stay in properly all it did was 9.15kN as the lobes pushed the axles U-shaped as they rotated to their full expansion and tipped out (at which point it slipped out of the fixture. Mind you, the cam was rated at 12kN. I did a couple more of them as well, and all of them did the same thing. I have video of it squirreled away somewhere that clearly shows the problem, so I'll post a link if I can find where I archived it.

BTW, this issue was corrected in the single stem Pre-C4 Camalots that replaced the U-stem ones, as the axles in the single stem ones are constant diameter and bear directly on the opposing lobe to give more support and are therefore more resistant to bending like the U-stem axles.

Pic of a Green U-stem Camalot after slipping from the fixture:

Green U-stem Camalot after slipping from the test fixture

Pic of the deformed axles:
Deformed axles from Green U-stem Camalot that slipped from the test fixture

Pic showing the space between the lobe and opposing axle:
Pic showing the clearance between the axle and lobe in a Green U-stem Camalot

Pic showing just how large the divot is (keep in mind that it's the _small_ diameter of the opposing axle that would bear on theedge of the slot, not the _large_ diameter):
Pic showing the size of the assembly divot on a Green U-stem Camalot

Aric Datesman · · Unknown Hometown · Joined Sep 2008 · Points: 145

@Abram- Found the video and tossed it up on YouTube for you. It's painfully obvious what's happening as the test progresses, and is why I think BD should recall them.

youtube.com/watch?v=AsExl8t…

Steve86 · · Unknown Hometown · Joined Jul 2011 · Points: 10

@Aric

Yikes, that's pretty scary. Thanks for posting the video, makes the failure mode a lot more obvious.

Aric Datesman · · Unknown Hometown · Joined Sep 2008 · Points: 145
Steve86 wrote:Yikes, that's pretty scary. Thanks for posting the video, makes the failure mode a lot more obvious.
That it does. Sadly the only response I got from BD was a rather heated discussion with Russ Clune at the NRR a few years back, who was none too happy about me having the remains of the cams and an explanation of how and why they failed on display. He was of the opinion the tests were invalid because the cams being tested were used and had an unknown history, while I see them as good sample of what's currently out in the field (especially when the failure stems from a rather obvious design flaw). We ultimately agreed to disagree and I was asked a short while later to remove all of the BD gear from the display. BTW, when I first posted this on RC ages ago I stopped short of calling it a design flaw mostly due to not wanting to make trouble for the folks at BD. The discussion with Russ left a bad taste in my mouth WRT BD, hence my taking a harder stance nowadays.
Steve86 · · Unknown Hometown · Joined Jul 2011 · Points: 10

I can understand why you'd feel that way. The "unknown origin" argument is a pretty weak argument considering the failure mode. If you had just popped a sewn sling or a trigger wire or something "soft", that argument would hold a lot more water. It's hard to imagine a set of reasonable or unreasonable circumstances that would affect the cam enough to fail in the manner displayed without serious predisposition to that failure mode.

If they disagreed with you that much they should have just pull tested some of their historical stock (I'm sure they have some of every generation/model around) where there is no question as to the origin. Maybe it was a freak occurrence. Guess we'll never know.

Speaking of which, is there anyway to access your old tests/videos? I didn't start reading climbing forums until you removed your stuff from RC but as an engineer by education I enjoy reading about the testing of gear. I know your site has some links to tests compiled by others but couldn't find any of yours.

Thanks again for posting the video.

Aric Datesman · · Unknown Hometown · Joined Sep 2008 · Points: 145
Steve86 wrote:Speaking of which, is there anyway to access your old tests/videos?
At the moment, no. Plan was to migrate all of it to TheClimbingLab.com, but the baby allows me little free time for that sort of thing.
Abram Herman · · Grand Junction, CO · Joined May 2009 · Points: 20

Thanks for the extra info & video, Aric. That video is of the cam you mentioned that pulled out at a little over 9kn?

Aric Datesman · · Unknown Hometown · Joined Sep 2008 · Points: 145
Abram Herman wrote:That video is of the cam you mentioned that pulled out at a little over 9kn?
Yup. I don't recall what the other ones pulled at, but all were a good bit below rating and exhibited the same failure mode.

On a side note, the only sizes I've tested were purple and green (.5 and .75) and I'd possibly be less grumpy about it if they were rated at 8kN rather than 12kN (as current designs usually are). But given the failure mode when placed at over 50% expansion and 12kN rating I've got a bug up my ass about it.

-a.
Ray Pinpillage · · West Egg · Joined Jul 2010 · Points: 180

How much force does it take to get the U-Stem to fail with a drop test?

Aric Datesman · · Unknown Hometown · Joined Sep 2008 · Points: 145

Not to ask a loaded question, but does it matter how it's loaded?

(to not run afoul of Rule #1 I'll volunteer that I have yet to see data that supports there being a difference since the dynamic climbing rope by definition limits the impact force on the piece)

Ray Pinpillage · · West Egg · Joined Jul 2010 · Points: 180
Aric Datesman wrote:Not to ask a loaded question, but does it matter how it's loaded? (to not run afoul of Rule #1 I'll volunteer that I have yet to see data that supports there being a difference since the dynamic climbing rope by definition limits the impact force on the piece)
I just assumed there was a difference and that you'd tested both ways.
Aric Datesman · · Unknown Hometown · Joined Sep 2008 · Points: 145

@Ray- nope, only did a slow pull since that's how the UIAA tests cams.

Pat Langendorfer · · Muncie, IN · Joined Feb 2009 · Points: 35

We should re-title this whole thread "yet another way to make trad climbing scary".
on a separate note, you can always send your cams back to BD if you're worried about them. Shipping cost is a small price to pay for peace of mind and un-broken bones.

Bill Czajkowski · · Albuquerque, NM · Joined Oct 2008 · Points: 20
Matt J wrote:How convenient, I was just going to ask the same question. I dropped this near new cam down a 200ft slab, it bounced around alot and landed in the dirt. I'm sure it should be retired, I hear cams get micro cracks and can just snap at any moment? Other than the obvious, there is no other visual damage, it still operates as smooth as it was before. It looks like one of the axles was bent/stretched. There is some play between the lobes but everything seems to be intact. What do ya'll think?
Be happy to take it off your hands.
Gunkiemike · · Unknown Hometown · Joined Jul 2009 · Points: 3,492
Bill Czajkowski wrote: Be happy to take it off your hands.
I suspect that cam has died of old age by now.
Guideline #1: Don't be a jerk.

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