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Re: [adatesman] Pull Test Results: Purple Golden Spiral Cam
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dingus


Nov 17, 2008, 11:18 AM
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Re: [adatesman] Pull Test Results: Purple Golden Spiral Cam
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thanks for the work and the posting

DMT


johnwesely


Nov 17, 2008, 11:18 AM
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Thank you for unlocking the power of the golden spiral
Wink


xtremst80


Nov 17, 2008, 11:22 AM
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Nice work! Good read Wink


jeepnphreak


Nov 17, 2008, 11:39 AM
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Nice, glade to see that the cam held up to what its susposed to.

whatcha do to you thumb nail, looks like that hurt


zonie


Nov 17, 2008, 11:41 AM
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Outstanding report.

One question: what did you do to your thumb?


dingus


Nov 17, 2008, 12:36 PM
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BTW, this thread dispelled even a wisp of an urge to maybe try one of these cams out.

They are so 'garage-80s!'

DMT


adatesman


Nov 17, 2008, 12:58 PM
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tigerlilly


Nov 17, 2008, 1:16 PM
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adatesman wrote:
But to put things in perspective, prices on the GS website run from $52-$54 and you can get Aliens from EMS for $60 or Zeros from MGear for $64. Maybe if they lowered their prices some and/or finished them a bit better, but given that small of a difference I don't see it happening.

I paid less than sticker price on Ebay for the sacrificial lamb. I forget exactly what, but it was in the vicinity of $40. Seems some joker nudged the price up a bit - that one was the only GS cam I saw anyone bid on at the time, and the opening price was 30-something. At that price, they might be interesting to the budget-conscious, if the mfr. can get a CE certification (and get rid of that silly white sleeve).

Kathy


Carnage


Nov 17, 2008, 1:48 PM
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im not too up on the science of stuff here(being a computer engineer) but i did notice something when watching the video.

it seems the cam's head starts to move down very early( when the display's readout is at 768(lbs?) at about 0:27 in the video)

i think this is because of either the axle bending or the lobes being compressed. assumption of units is correct, thats the equivalent of taking a fall factor .05 (using a 80kg climber and some messing around on the petzl fall simulator). this is pretty easily achievable, so although the cam will hold, it almost seems like it is disposable.

after you fall on it once, you gotta buy a new one Unsure

forgive me if i've missed something, im a newish trad leader still figuring things out.


kennoyce


Nov 17, 2008, 2:19 PM
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I watched the video to see what you mean as I also started to see movement around the same value that you stated. The thing that I noticed though is that the cam started to move at that point, and continued to move until it broke, this suggests to me that it was still within the elastic area, and had not yet yielded meaning that as soon as it was unloaded it would just spring back to its original shape. I really can't know the point of yielding based on the video, but I would be willing to bet that it would be fine for at least another 500 lbs or so with no noticeable deformation upon removal of the load.


Partner cracklover


Nov 17, 2008, 2:32 PM
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Re: [adatesman] Pull Test Results: Purple Golden Spiral Cam [In reply to]
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Cool, thanks for sharing. An interesting issue:

adatesman wrote:
When you watch the video you can clearly hear the point where the strands start to break, which corresponds to the big dip in the force chart.

This shows that the cam actually started to fail by way of wires pulling out of the swage slightly below the rated breaking strength of the piece.

This shows that, at least in this case, testing something to below, but close to its rated holding ability may compromise the physical integrity of the piece.

Not surprising, of course, but interesting to see proven.

Cheers!

GO


adatesman


Nov 17, 2008, 3:19 PM
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adatesman


Nov 18, 2008, 7:43 AM
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Partner cracklover


Nov 18, 2008, 8:04 AM
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adatesman, interesting!

The thing is, even though, in this case, it did wind up exceeding the rated strength before breaking, I'm far from convinced that a piece that has had its physical integrity compromised to the degree that this cam did while still below the rated strength, would continue to function properly in the field.

It seems very likely to me that after the strands start to pull through the swage, if the cam is just carried around on a rack, placed, lightly loaded with body weight, etc, that the strands of the cable would continue to move around, separating more from each other and from the sleeve. Much like a cable with a crimped end sleeve will stay fine forever, but once that end sleeve comes off a little, the cable will fray more and more from normal use.

And if the movement folks were seeing starting at low loads was due to the cable beginning to slip in the swage, then I'd consider these cams to be total garbage.

GO


Partner cracklover


Nov 18, 2008, 8:14 AM
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I have a question about your pull testing machine. How evenly does the force increase?

Because when I look at this graph:



I see a very uneven increase in loading. If that's not due to the machine itself, then something else must be slipping to drop the load. The only possible causes I can think of are: the head of the cam slipping down in your vice; the cable itself stretching; or the cable pulling/shearing from the swage.

If it's the last of the three, and it's starting at 500 lbs of force... Well that's terrible, don't you think?

A good way to test this would be to get another one of these, mark the cable precisely where it enters, load it several times in increasing amounts (but under the breaking strength), and then check your mark after each test to measure the cable slippage.

GO


adatesman


Nov 18, 2008, 9:28 AM
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curtis_g


Nov 18, 2008, 9:58 AM
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If only I had unmonitored access to the $20k test rigs in my materials lab here at the U of I.

Is there any dependence of modulus or UTS on the loading rate?


Partner cracklover


Nov 18, 2008, 9:59 AM
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adatesman wrote:
I guess first thing I'd say is that the graph clearly shows a known deficiency in my test rig- the pump and ram are el-cheapo brand with crappy hydraulic seals that leak. So being a hand pump, the moment I pull the lever back for the next stroke the seals begin to leak and the force begins to drop a bit. So knowing that is the case, I think its safe to ignore the small, regular dips in the graph as system-induced noise.

Okay, that settles that question - thanks!

GO


adatesman


Nov 18, 2008, 10:20 AM
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curtis_g


Nov 18, 2008, 10:21 PM
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adatesman wrote:
curtis_g wrote:
If only I had unmonitored access to the $20k test rigs in my materials lab here at the U of I.

Is there any dependence of modulus or UTS on the loading rate?

Heh.... For a paltry $18k you could have one of your very own on Ebay: 20,000 lb capacity Instron 1125 Pull Tester

If only I had that kind of budget.... Frown Smile

Quality set of various grips not included.

Our favorite question for the lab manager is how much all the stuff we're playing with costs. And that's only the instructional lab...


jrathfon


Nov 19, 2008, 7:36 AM
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tigerlilly wrote:
adatesman wrote:
But to put things in perspective, prices on the GS website run from $52-$54 and you can get Aliens from EMS for $60 or Zeros from MGear for $64. Maybe if they lowered their prices some and/or finished them a bit better, but given that small of a difference I don't see it happening.

I paid less than sticker price on Ebay for the sacrificial lamb. I forget exactly what, but it was in the vicinity of $40. Seems some joker nudged the price up a bit - that one was the only GS cam I saw anyone bid on at the time, and the opening price was 30-something. At that price, they might be interesting to the budget-conscious, if the mfr. can get a CE certification (and get rid of that silly white sleeve).

Kathy

Did you report that shill bidding? If that's the company pulling that BS, there's one more reason not to buy their product! Look up shill bidding on eBay's help pages, they give perps the boot and press charges without hesitation.

You are saying that there were multiple cam units at their starting $30, yet the only cam the 3rd party bid on was the cam you had already placed a bid on? Super suspicious.


tigerlilly


Nov 20, 2008, 5:40 PM
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jrathfon wrote:
tigerlilly wrote:
adatesman wrote:
But to put things in perspective, prices on the GS website run from $52-$54 and you can get Aliens from EMS for $60 or Zeros from MGear for $64. Maybe if they lowered their prices some and/or finished them a bit better, but given that small of a difference I don't see it happening.

I paid less than sticker price on Ebay for the sacrificial lamb. I forget exactly what, but it was in the vicinity of $40. Seems some joker nudged the price up a bit - that one was the only GS cam I saw anyone bid on at the time, and the opening price was 30-something. At that price, they might be interesting to the budget-conscious, if the mfr. can get a CE certification (and get rid of that silly white sleeve).

Kathy

Did you report that shill bidding? If that's the company pulling that BS, there's one more reason not to buy their product! Look up shill bidding on eBay's help pages, they give perps the boot and press charges without hesitation.

You are saying that there were multiple cam units at their starting $30, yet the only cam the 3rd party bid on was the cam you had already placed a bid on? Super suspicious.

I wish I had known that at the time, as I could have documented what was happening. I don't have any evidence now. Thanks for the education. I had written it off as the wild, wild web in action.

Kathy


gunkiemike


Nov 22, 2008, 4:59 PM
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adatesman wrote:

On a somewhat unrelated note, I'm a bit perplexed by the force the cable broke at.... Their website clearly states that its stainless 5/32" 7x19 cable, but every supplier I look at only has that size/construction in a 2400 pound breaking strength rating. So even assuming the swage gave 100% strength (which appears to be the case since the cable broke) that still puts the cable breaking 9.4% above its rating. I was under the impression that cable strength ratings had no built-in safety factor, but maybe they still fudge things a bit to make sure they exceed the spec?

Hmmm.....

Even if they don't have a "safety margin" per se (3:1, 5:1 etc) like a lot of things, that rated strength is still subject to variation. Maybe 2400 lb is the AVERAGE of all tests. In that case some will withstand a bit more (and some a bit less, duh). Or maybe they use a 6 sigma metric. In which case it had damn well better break above that value. Or maybe it's just their MBS - minimum breaking strength.


notapplicable


Aug 15, 2010, 4:05 PM
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PDF of google cached thread containing posts deleted by Aric.

http://www.keepandshare.com/...10-7-02-pm-652k?da=y


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