Sunshine wrote:Here's something to keep in mind. Look closely at loose/spinning hangers. When they are repeatedly fallen on, hung from, or TR'ed from, the spinning hanger will wear into the bolt. When I replaced the anchor on Wadcutter the bolt with the spinning hanger broke with very little force. The other bolt was fine.
Good point!
If any of you find a spinner on a climb in Muir, please report it to me, t_bone, jrock, or any of the other route developers there. We will correct the problem as soon as possible.
We should point out here that a spinning hanger bracket does not necessarily mean that the bolt has loosened in its hole. But, over time, in some installations, the bolt can loosen and create a dangerously weak hanger.
How does this happen?
Consider a typical bolted hanger, for example, a FIXE hanger bracket affixed to the wall with a sleeve bolt. Some wooly mammoth (no offense, Neil) takes a whipper and yanks this bracket around a few degrees. This causes the weak sandstone interface between the hanger bracket and rock wall to disintegrate. Once this happens, it becomes easier and easier to pivot the hanger, grinding out more sandstone, until it spins freely. For a while, the bolt may remain secured as solidly as it was when it was installed. Eventually, it can loosen.
The sleeve bolt achieves its "lock" on the wall when the bolt is tightened against the hanger and draws a cone plug into the bolt's sleeve. The sleeve compresses against the surface of the hole. The resulting friction between the sleeve and hole secures the bolt to the rock.
After a hanger spins free, a small gap exists between the bottom of the bolt head and the hanger. This allows the cone to retreat back into the hole and lessen its squeeze on the sleeve. This reduces the frictional force between the sleeve and the hole, and the bolt can loosen. Note that the cone may not retreat, but why take chances?
And, "Sunshine" has given us one more reason for not letting spinners go uncorrected.
Rick
