Method and cable anchor assembly for anchoring plastic coated rope

A cable anchor assembly for use in anchoring plastic coated rope to alternatively carry a load in oil well drilling derricks and the like and also to allow the plastic coated rope to be selectively slipped or fed through the cable anchor assembly for replacement thereof, comprising

• a base,
• a snubbing drum and clamp means mounted on the base, the drum having a spiral groove formed on a cylindrical surface of the drum for receiving the plastic coated rope wound thereabout and for engaging and anchoring the rope, the clamp means being arranged for engaging the rope opposite the drum from the rope load,
• the spiral groove being formed with an included angle in the range of from about 136 degrees to about 165 degrees for developing substantial frictional engagement with the plastic coated rope while still permitting selective slippage of the rope in the groove when feeding the rope through the cable anchor assembly,
• the groove being formed with at least three turns on the cylindrical drum surface which are engaged by the plastic coated rope, and
• the clamp means comprising a clamp housing fixed relative to the snubbing drum, insert means arranged within the clamp housing for engaging the rope and means for applying clamping force to the rope through the insert means,
• the radius of the plastic coated rope being greater than the radius of the spiral groove whereby a "pinch effect" is produced between the spiral groove and plastic coated rope in order to maintain desired frictional engagement therebetween.

A method for anchoring plastic coated rope to alternatively carry a load in oil well drilling derricks and the like and also to allow the plastic coated rope to be selectively slipped or fed through the cable anchor assembly for replacement thereof, comprising the steps of

• mounting a snubbing drum and clamp means on a base structure to resist the rope load, the drum having a spiral groove formed on a cylindrical surface of the drum for receiving the plastic coated rope wound thereabout for engaging and anchoring the rope, the clamp means being arranged for engaging the rope opposite the drum from the rope load,
• forming the spiral groove with an included angle in the range of 136 to 165 degrees for developing substantial frictional engagement with the plastic coated rope while still permitting selective slippage of the cable in the groove when feeding the rope through the anchor assembly, and
• forming at least three groove turns which are engaged by the plastic coated rope about the cylindrical surface of the drum, the number of turns being selected for normally supporting most of the rope load whereby the clamp engages the rope with a force to prevent damage to the rope,
• the radius of the plastic coated rope being greater than the radius of the spiral groove whereby a "pinch effect" is produced between the spiral groove and plastic coated rope in order to maintain desired frictional engagement therebetween.