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Aric's Alien break-fest:
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cracklover
Jun 21, 2009, 4:51 AM
Views: 19047
Registered: Nov 14, 2002
Posts: 10162
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For those of you interested in Aric's recent breaking of a bunch of Aliens, I did some work to collect some data on the effective angle of each cam he tested.
Edited to add: The angle I'm measuring is the angle between the center of the axle and the point of contact between the edge of the fixture at the moment before Aric began pulling.
Hopefully this pic will clarify. Depicted is the right side cam lobe, the axle, and the right side of the fixture. The angle I'm measuring is the angle between the axle and the fixture at the moment before the cam starts getting pulled.
Methodology:
I used the photos Aric scanned in of the cam lobes post-pulling, found here: http://www.shariconglobal.com/...cans/lobe_scans.html
Second, I ran these photos through the Dorrington software to obtain a theoretical center point. (found here: http://www.dorringtonclimbing.com
Third, I found the contact point for each lobe, using a combination of the photos Aric took of the cam placed in the jig, and the flat spot on the cam lobe. Wherever possible, I used the actual flat spot.
Fourth, I determined the effective cam angle in the jig for each lobe, and averaged them together. For each cam Aric put photos online, I used between two and four lobes. If the lobes were too bent, or if the results were identical across lobes, I did not use all four.
Lastly, I averaged these angles together to find the effective cam angle for each piece Aric tested.
The reasons these photos are more accurate to run through the Dorrington software are four-fold. First, because they are layed flat on a scanner, they are properly oriented to the "camera". Second, because the axle and nut are removed, leaving the axle hole in the same plane, the center of the stem cannot "appear" to be offset due to a slight change in camera angle. The center of the axle is exactly where it is. Third, the flat spot in the cam lobe shows exactly where the lobe contacted the fixture. This is much superior to the guesswork of looking at a photo of the cam in the fixture and trying to estimate where lobes that are hidden by the closer lobes are contacting the fixture. And lastly, in some cases, the different lobes were cammed quite different amounts. Looking at the cams after the fact made this obvious, and gave much more accurate readings on where the contact point is. I was then able to average the angles together.
With all that said, here is the raw data:
sample size failure angle RATING
Number mode %
7 black pulled 19.3 64%
24 black pulled 21.0 54%
22 blue pulled 13.0 83%
23 blue pulled 18.2 69%
6 clear pulled 18.8 90%
17 grey pulled 21.5 98%
19 grey pulled 21.8 105%
2 orange pulled 14.8 74%
4 purple pulled 21.7 81%
5 purple pulled 22.7 89%
14 red broke cable 19.7 101%
12 red broke cable 19.8 100%
15 red/silver pulled 19.3 113%
16 red/silver broke cable 19.5 117%
21 yellow pulled 17.2 105%
9 yellow pulled 18.3 94%
3 yellow braze 18.5 78%
20 yellow pulled 18.7 83%
8 yellow pulled 18.8 93%
Looks like within a cam size, there may be some correlation between angle and pullout force, such that the higher the angle, the lower the force. But I'm tired, and I haven't run the numbers.
Here are the pics:
http://s26.photobucket.com/...gles/?albumview=grid
GO
(This post was edited by cracklover on Jun 22, 2009, 6:47 PM)
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Edit Log:
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Post edited by cracklover
() on Jun 22, 2009, 6:47 PM
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