Vertical caving terminology and methods > Rigging methods and equipment
A device for removing anchors that have become damaged or obsolete, ideally without damaging the rock that they were placed into. The exact approach will depend on the type of anchor and how it has been placed. It is common to drill the hole for a through bolt deeper than it needs to be when installing it, so that when it is no longer needed, it can be loosened, and hit in further with a hammer to bury it below the surface. The exposed part of an anchor may be cut off with an angle grinder. A hollow drill bit may be used to encircle the anchor, drilling a slightly wider hole into the rock, with the anchor nestled in its centre, removing it like an apple core. A drill may be used to remove rock next to the anchor, then the anchor may be hit sideways into the new hole to free it. A bolt may be screwed very hard into a spit, pushing against its wedge to force the spit nut to move outwards, out of the rock. A hardened metal cutting drill bit may be used to drill away the metal of a spit. In all of these cases, resin may then be used to fill the hole, and hide it. However, if the hole is not reused, then it effectively compromises the surrounding rock, preventing a new anchor from being placed in a similar position, and causing bolt rash.
A dedicated extractor may rely on some types of anchor being prevented from gripping the rock, such as using heat to damage the resin of a P-hanger, or using a drill to rotate a through bolt so that its expansion sleeve cuts into the metal wedge, preventing it from expanding properly. The bolt extractor tool is then used to pull the anchor outwards with a lot of force, pushing against the rock surrounding the anchor so that the rock remains intact rather than being fractured. Typically, these work by tightening a nut on a screw threaded rod, with the rod pulling on the anchor, and the nut resting on a housing that pushes against the rock around the anchor. In particular, the IC anchor and discontinued DMM branded Eco anchor are P-hangers that are designed to be removable from the rock in this way, leaving a hole that can be reused for a new anchor, keeping it in the same position as the previous one. This is why they are approved by the Council for the Northern Caving Community. The success rate with through bolts is much lower, and they may still grip the rock, causing it to be destroyed as they are pulled.
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