Inventors:
Charles R. Griste - Corsicana TX
Assignee:
Hughes Tool Company - Houston TX
International Classification:
B23Q 5027
B23Q 5033
Abstract:
A downcrowding device for an earth boring apparatus has an improved take-up device for taking up slack in the downcrowding cable. The downcrowding device is of the type having a rotatable drum, hydraulic rams for moving the drum downwardly, a brake for preventing rotation of the drum while moving downwardly, and a downcrowding cable that is connected directly to the top of the kelly and wrapped around the drum. The take-up device includes a take-up sheave that is suspended from the mast. A take-up cable is wrapped around the drum for rotating the drum in the opposite direction to the downcrowding cable. The take-up cable is reeved over the take-up sheave and is connected to the top of the kelly. The cable tensioner is located between the mast and the take-up sheave for allowing the sheave to move downwardly with respect to the mast as the kelly and drum move downwardly during drilling. The cable tensioner draws the take-up sheave upwardly with respect to the mast to rotate the drum and take up slack as the drum is moved upwardly with the brake released.