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Old 12-20-08, 04:29 PM   #1
High Fist Shin
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Crank set needs stress relief

Saw this in the For Sale forum:

"Campy SR 170mm 53/42 rings. MUST BE STRESS RELIEVED. If you dont know what 'needs to be stress relieved' means do not buy and do not ask."

Ok, I'll admit I don't know what "stress relieved" means. Can someone kindly enlighten me?

Dan
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Old 12-20-08, 04:42 PM   #2
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This makes my "BS" meter read rather high.
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Old 12-20-08, 04:48 PM   #3
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I think it means " If you are looking for a usable crank then don't buy these".
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Old 12-20-08, 04:49 PM   #4
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Ok, "BS" or not, what does it mean? I've never heard of stress relieving a crank or rings or whatever.
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Old 12-20-08, 05:27 PM   #5
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I don't think it means anything. You can stress relieve wheels, but thats because they have different parts held together under tension. Cranks don't. Obviously that the post is really some sort of covert spy transaction.
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Old 12-20-08, 06:06 PM   #6
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Campy cranks of that era are known to develop micro cracks where the crank attaches to the spider, a "stress crack". Folks keep the crack from running by grinding away the cracked area. I've never had to do this to my NR cranks so my description might be inaccurate. So the seller is sayin' the crankset has a crack in it...

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Old 12-20-08, 07:20 PM   #7
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Originally Posted by cranky old road View Post
Campy cranks of that era are known to develop micro cracks where the crank attaches to the spider, a "stress crack". Folks keep the crack from running by grinding away the cracked area. I've never had to do this to my NR cranks so my description might be inaccurate. So the seller is sayin' the crankset has a crack in it...
Thank you. I wasn't aware of this as I've never had Campy cranks on my vintage bikes.
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Old 12-20-08, 07:25 PM   #8
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Originally Posted by cranky old road View Post
Campy cranks of that era are known to develop micro cracks where the crank attaches to the spider, a "stress crack". Folks keep the crack from running by grinding away the cracked area. I've never had to do this to my NR cranks so my description might be inaccurate. So the seller is sayin' the crankset has a crack in it...
Good information................thanks.
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Old 12-20-08, 08:18 PM   #9
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All of my NR cranks had that little crank, back in the 70's. Get a 3/16 inch small rat-tail file and radius the little web aluminum where the arm joins the spider, then use emery paper on the file and polish up what you file, you will likely file that the crack is very shallow and disappears after the filing... FYI i never heard of the cranks breaking at this spot
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Old 12-20-08, 08:56 PM   #10
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Generally in metal working stress relieved means bead blasting the to relieve stresses that could lead to cracks in the metal. Roger
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Old 12-21-08, 09:45 AM   #11
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Generally in metal working stress relieved means bead blasting the to relieve stresses that could lead to cracks in the metal. Roger
I often also means heat-treating the part after cold working or forging to relieve the internal stresses.
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Old 12-21-08, 11:32 AM   #12
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Generally in metal working stress relieved means bead blasting the to relieve stresses that could lead to cracks in the metal. Roger
Bead blasting actually imposes a stress, not relieves it.

Mac
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Old 12-21-08, 11:43 AM   #13
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Why didn't you just ask the OP of the cranks, he seemed more than happy to explain.
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Old 12-22-08, 11:03 AM   #14
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There are lots of ways to remove stress.It can be done with temperature,sound waves,shot peening,vibration.Depends on what kind of stress your trying to get rid of.If your trying to eliminate stress cracks,the best way is to shot peen.That will compact the metal and spread the stress over a larger area.
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Old 12-22-08, 12:09 PM   #15
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Bead blasting actually imposes a stress, not relieves it.

Mac
It doesn't do either; it peens the surface to eliminate small voids that could become stress risers.

It also work-hardens the surface slightly.
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Old 12-22-08, 06:09 PM   #16
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Why didn't you just ask the OP of the cranks, he seemed more than happy to explain.
Well he wrote:"If you dont know what 'needs to be stress relieved' means do not buy and do not ask."

To me that means he doesn't know either and doesn't want to have to admit it.
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Old 12-22-08, 06:15 PM   #17
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I think he just wants to be an elite prick.
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Old 12-22-08, 08:29 PM   #18
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The difference between bead blasting and shot peening needs to be clarified in this thread.
http://www.speedwaymotors.com/METAL-...INET,2606.html
http://www.metalimprovement.com/shot_peening.php

OT, but a new one for me is laser peening:
http://www.metalimprovement.com/laserpeening.php

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Old 12-23-08, 11:34 AM   #19
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The difference between bead blasting and shot peening needs to be clarified in this thread.


OT, but a new one for me is laser peening:
http://www.metalimprovement.com/laserpeening.php
Really just a difference in the blasting media being used; the techniques and the results are pretty similar.

The laser technology is interesting; with the temperture component there might be a slight surface tempering effect as well as the mechanical effects.
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