Importance

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Abstract

A drilling apparatus of the type including a platform, a pair of spaced, parallel, substantially vertical guide rails, and a power swivel which is guided along the guide rails is provided with a pair of space support surfaces positioned on the underside of the swivel. In addition, a pair of collapsible pedestals are mounted on the platform, each pedestal positioned under a respective support surface such that the swivel rests on the pedestals when lowered toward the platform. These pedestals are provided with a collapse strength chosen such that the pedestals collapse in a controlled, progressive manner, substantially without damage to the guide rails, in the event the swivel falls from at least a predetermined height. In this way both the platform and any drill string attached to the swivel are protected from excessive loads associated with abrupt deceleration of the swivel, and the incidence of string breakage due to such abrupt deceleration is at least substantially reduced.

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First Claim