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bigo
Aug 6, 2009, 2:25 PM
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atlnq9 wrote: Finally people can stop telling me I am full of crap and actually realize how brittle these lobes are. If you can break them with a hand and a vice then that says they are definitely not safe in anything but a textbook vertical placement. Thanks adatesman and Healyje for the cam and the test. So when does it become better to just bring two cams?
I don't think people here realize the implications of a brittle material vs a ductile material for a failure mode. I understand the point you are making; unfortunately I don't think others are.
Material strength is only one parameter of a design that controls a failure mode. Ductility or lack of, stress concentrations due to geometry, how the load path(s) change during yielding/failure, all are just as important for determining the strength of a component.
While it is certainly clear that the design of the link cam suffers from an inherent weakness that will likely make any cam with a similar design vulnerable to bending of the extended cams, it is incorrect to say that the design could not be improved to make a more robust cam that is resistant to the catastrophic failures that seem to happen with the OP cam.
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adatesman
Aug 6, 2009, 3:18 PM
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bigo
Aug 6, 2009, 3:40 PM
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adatesman wrote: patto wrote: But I do disagree with you that 'OP is going to give it a long, hard look'. Perhaps I use the term "trust they'll...." a bit differently than some. It's more of a hope and expectation kind of thing. That said, I'd be satisfied with them simply saying not to place them such that the lobes can get loaded sideways. Anyway, snapped 2 more this morning and it looks like the one last night wasn't a fluke. Both snapped within 15% of what a calculation using rough measurements of the distances involved said they would, which is close enough for me.
Did they yield much before they broke?
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adatesman
Aug 6, 2009, 3:47 PM
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curt
Aug 6, 2009, 3:59 PM
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majid_sabet wrote: you do not need to be an engineer to figure this out but anytime you have a mechanical device that has too many moving parts, connections, attachments and linkages, and this device is going to be used for climbing and with potential of falling, then you are asking for trouble.
This exact same comment was made when the original rigid-stem Friends first came out.
Curt
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adatesman
Aug 6, 2009, 4:10 PM
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bigo
Aug 6, 2009, 4:23 PM
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adatesman wrote: bigo wrote: Did they yield much before they broke? Not from the look of it. I wouldn't expect it to either, given the pics earlier in the thread that showed what looked to be a brittle failure.
Great, thanks again for the info. I wouldn't have expected much either.
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majid_sabet
Aug 6, 2009, 5:05 PM
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curt wrote: majid_sabet wrote: you do not need to be an engineer to figure this out but anytime you have a mechanical device that has too many moving parts, connections, attachments and linkages, and this device is going to be used for climbing and with potential of falling, then you are asking for trouble. This exact same comment was made when the original rigid-stem Friends first came out. Curt
Curt
I am sure such comment were made back then but look at the number of the moving parts on that cam vs the others. All it takes is one lob to fail or a rivet to pop and the entire device fails.
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healyje
Aug 6, 2009, 6:43 PM
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adatesman wrote: [ 3. Clamped the edge of the outermost link in a vice (only inserted 1/8" and in the middle of the curve) 4. Curled the linkage such that the smallest link meshed with the middle one 5. Pulled parallel with the axle using the sling.
Oh - Aric, that isn't the test I hoped you'd do. I knew for sure they'd break that way - nothing would withstand that test. When I said 'break with just my hands', I meant one cam lobe segment in one hand and another cam lobe segment in the other - not involving the stem in any way. What I was hoping you'd test was clamping an inner lobe in a vise and trying to break an outer lobe off by hand.
The test you did clamping an outer cam lobe section in a vise and pulling on the sling, I bet most conventional SLCDs above about 1" or so would also fail that same test.
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adatesman
Aug 6, 2009, 8:19 PM
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healyje
Aug 6, 2009, 8:36 PM
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adatesman wrote: Well, I've got one lobe left. Back in a sec. EDIT- Nope, no dice. All I succeeded in doing was hurting my hand. Procedure was clamp the stem in the vice, unfurl the remaining linkage upward and then push/pull sideways on the end. Adding a pliers into the mix made it easy, so perhaps someone more manly than me would have succeeded.  
Ah, good, and going to pliers would have been the next step. So pliers on one cam lobe segment with the other segment in a vice breaks. Then my question would be do you think any alloy / treament combination wouldn't break similarly.
I'm just fishing for boundary conditions as I'd climb on them as is, but would only use them in clean placements.
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bonner1040
Aug 6, 2009, 9:05 PM
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Dingus... can i buy your link cams?
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adatesman
Aug 6, 2009, 9:10 PM
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Bradly
Sep 7, 2009, 5:54 PM
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Hello all,
I got an official report from Michael and the folks at OP about two weeks ago and I was hoping Michael would come on here and tell you all what it says, and I'm sure he will elaborate on this post.
(If someone wants to tell me how to extract photos from a pdf file I will share the photos, which are really good and tell a lot.)
From OP:
"INSPECTION:
All component parts were inspected to ensure compliance with drawing and assembly specifications. Additional hardness testing was performed to ensure
the parts were not beyond acceptable criteria. All assembly processes were complied properly.
Initial inspection of the parts indicates that the cam was placed in a manner that allowed the force of the fall to load at an angle across the lobes creating force
from the side. We have conducted—and continue to perform—tests to ascertain the failure point of our links in a variety of real-world climbing scenarios. These tests are ongoing and data is still being collected. However, we’ve found that, in compromised placements, where the linkages are leveraged over
edges; the cam head is prevented from shifting into direction of pull during a sudden load; or the
cam linkages absorb a side load, failure can occur. In some cases, a load of only a few hundred
pounds of force was enough to cause damage.
It should be noted, however, that when placed in anticipation of direction of pull, the cams
were strong to over their rated strength.
CONCLUSION:
Individually, the photos in this report do not explain what could have occured. Collectively, though, they may provide clues into what happened to this cam just before it was damaged. Combined with our knowledge of how links respond to side loads or placements that don’t permit adequate re-orientation of the cam, we believe the following occurred.
Key points are found in photos #7 and #5.
The marks in photo #7 appear to be recent and, likely, the last thing to happen to this cam. The
angle of the marks suggest a shifting of this cam occurred, under load, into the direction of pull,
during the fall that claimed it. This suggests that the cam wasn’t placed in direction of pull (the stem pointing directly to the ground) at the time it was loaded (i.e. the climber fell). This set into motion a short series of events that is indicated by the small amount of damage visible in Photo #5. That mark suggests that the Lobe Set was damaged before the cam completed its rotation into direction of pull as there is a clear mark on link #1 where a damaged
link #2 was driven into link #1.
We surmise that the two broken Lobe Sets were the pair that was oriented in the bottom of the placement as the marks suggest so, as do our test results; it’s almost always the bottom pair of Lobe Sets that become damaged when subjected to these kinds of loads. It’s possible that the cam wasn’t able to shift into proper position because the feature was
bottoming and the head of the unit was unable to rotate enough to put the stem into proper
direction. It’s also possible that there was some obstruction at the bottom of the feature that
prevented the linkages from moving into proper direction. Regardless, some sort of limitation was
put onto the cam and the linkages gave way to the load from the side. It should be emphasized that although we’re talking about cams shifting into proper position, a climber should virtually NEVER plan for that to occur. Any cam and, particularly Link Cams,
should be placed deliberately and consistently in anticipation of the direction of pull EVERY TIME.
If the cam cannot be placed in that proper orientation, another piece should be used. It is possible that the climber in this instance placed the cam properly, but due to rope drag or walking of the cam, it may have reoriented itself into a compromised placement. Longer slings added to the cam during a lead may minimize this possibility.
In conclusion, this return has led to significant consideration from several departments within the
company about how best to:
a) improve the strength of the product as much as we can through design changes or
alternative materials. Several options are being carefully researched and considered at
this time for introduction into subsequent versions of the Link Cam. Some may be introduced as inline changes in the next few months or less.
b) Adequately inform customers about the nature of Link Cams and the importance proper
placement has on whether the cams will be reliable or not. We have not found a single
Link Cam to fail prematurely when loaded properly, but we recognize that the distinction
between a “good” placement that will hold reliably and a “bad” placement can be somewhat indistinct, particularly when a climber is placing it on lead and in a stressful environment or situation. Our marketing department will be amending any literature
related to Link Cams to address the limitations of Link Cams more specifically so that climbers can become better-equipped to assess “good” and “bad” placements in the future. Catalog, hangtag, advertising and website changes will be forthcoming in the weeks and months to come.
We are certain that Link Cams, when placed in accordance to their intended design, are strong and safe, but we need to be sure to continue to improve the product as we can and make sure we educate climbers about the specific issues related to Link
Cam placements."
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JAB
Sep 10, 2009, 7:23 PM
Post #166 of 170
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Bradly wrote: (If someone wants to tell me how to extract photos from a pdf file I will share the photos, which are really good and tell a lot.) From OP:
Pics would be great. Do this to get them out of the PDF (assuming Adobe Reader 9):
1) Go to View->Toolbar->More tools
2) Scroll all the way down and check the snapshot tool
3) There is now a camera button on your Select & Zoom toolbar
4) Select the camera and paint over the picture you want to copy. When mouse is realeased, the area is copied to the clipboard.
5) Paste into favourite picture program and save as JPG
6) Upload it to RC.com!
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bearbreeder
Sep 15, 2009, 11:30 AM
Post #167 of 170
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Thanks for the information from everyone
Would love to know what OP is changing about the link cams as they indicated
As i just bought a full set and an wondering if there are any existing plans for the link cams already out
Thanks
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sonyhome
Sep 15, 2009, 6:26 PM
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My thanks too for posting this thread, and for the official Omega Pacific response.
I own a #1, and use it as my oh-shit piece/leftover anchor piece. I'll be sure to even pay more attention to its placement now.
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sonyhome
Sep 15, 2009, 6:57 PM
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Improving the linkcam?
- Loop or larger hole at end of stem to clip a carabiner or hook
- double loop runner
- More flexible stem, like BDs, would reduce the lever effect on sideways and horizontal placements. Maybe make only the top 1/2 of the stem rigid as a compromise to still allow trigger action, and reduce the length of the metal neck as much as feasible.
- #4->#6 cam: shorter stem with a pulley mechanism.
Put a roller on the cam lobe and loop a kevlar wire going to the base of the trigger, to reduce travel by 1/2. If the stem is anchor is too short then redirect a 3rd time back to the trigger. Possible because the cam becomes so big. Caveat: need more strength to pull the cam trigger. Consider that for #1 and #2 cams too.
- #4->#6 cam trigger lock:
Redesign the trigger mechanism with a hook so it can be racked pulled. For example with a pin that clicks-in.
-Sideways pulls: when the cam is somewhat retracted, the stem moves freely from the heads left to right, but not up-down. To allow up-down you'd need more of a ball joint. First you'd need to relocate the springs closer to the center to push outwards the inner lobes and provide room for the stem to move. Now you could insert a cylinder of elastic material that would givewhen there is an up-down pull, instead of a knuckle if that would be too hard to assemble.
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michaellane
Sep 17, 2009, 8:57 PM
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Howdy ...
Thanks for posting the report, Brad ... it pretty well sums up what we learned and determined regarding the issue of this post, but to reiterate a couple key points:
1) We can't get Link Cams to break below rating when they're pulled in proper direction.
2) They can fail below rating when the hinges are subjected to side or torquing forces, most often caused by loading the cam improperly.
3) The difference between "proper" and "improper" can, sometimes, be a little confusing, particularly to newer climbers.
In order to increase our margin of safety, we are looking at several upgrades to the hinges that involve dimensional modifications and potential materials changes, too. These improvements are being developed now and will be introduced in-line as development permits. The first of the modifications should be seen on the street in a couple months or so.
The improvements WILL make our cams more durable, but the truth is a) other cams with solid lobes will probably always be more durable and resist becoming damaged during weird loading better than Link Cams and b) you should always place cams of any design in such a way that they are loaded properly.
Improvements in our marketing literature to be more specific about proper and improper loads are in development, as well. We'll have the new information up on our website as soon as possible and, then, new hangtags will be included with each Link Cam sold.
Sonyhome ... thanks for the suggestions. You're pretty much spot-on with the majority of responses we've gotten from other climbers and we're working on implementing several of those changes right now. I don't have a release date to announce, but the changes are in development.
Thanks for everyone's interest in this matter. It may sound trite, but we really do value your support and feedback ... either good or bad. As always, if you've got questions about our gear, please contact us.
--ML
__________________________
Michael Lane
Omega Pacific
800.360.3990
info@omegapac.com
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