Bicycle Mechanics - 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

This makes my "BS" meter read rather high.

I think it means " If you are looking for a usable crank then don't buy these".

Ok, "BS" or not, what does it mean? I've never heard of stress relieving a crank or rings or whatever.

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.

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...

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.

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.

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

Generally in metal working stress relieved means bead blasting the to relieve stresses that could lead to cracks in the metal. Roger

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.

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

Why didn't you just ask the OP of the cranks, he seemed more than happy to explain. :)

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.

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.

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. :rolleyes:

I think he just wants to be an elite prick.

The difference between bead blasting and shot peening needs to be clarified in this thread.
http://www.speedwaymotors.com/METAL-BEAD-BLAST-CABINET,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

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.