SEISMIC METHODS 



873 



the drill assembly are indicated in Figure 546. Figure 547 is a photograph 

 of the same drill. 



The mechanism for imparting the rotation and the feed to the drill 

 pipe is illustrated in Figure 548. The drive rod (L) is a steel tube through 

 which the drill pipe (Q) passes. The outside of this drive rod is either 

 fluted or hexagonal in cross section so that it is free to travel vertically 

 through the drive rod bushing (M) at the same time that it is being 

 rotated by this bushing. The rotation of the drive rod bushing is derived 

 from the beveled gearing indicated at (N). The drill pipe is attached to 

 the drive rod by means of the chuck (A). The chuck is usually located at 

 the bottom of the drive rod, as indicated; but on some drill assemblies the 



Fig. 546. — General arrangement of a portable hydraulic-feed seismograph drill. 

 (Courtesy of Joy Manufacturing Company.) 



A. Drill chuck 



B. Operating controls 



C. Cat head 



D. Hoisting drum 



E. Mast 



F. Hydraulic mast raising cylinders 



G. Sheave for hoisting rope 



H. Sheave for cat line 



I. Mud pump 



J. Hydraulic oil tank 



K. Hydraulic feed cylinders 



chuck is at the top of the drive rod instead of at the bottom. The drill pipe 

 is attached to or released from the drive rod by tightening or loosening the 

 set screws (O). 



On some drill assemblies the hand-operated set screw type chuck is 

 replaced by a semi-automatic or fully automatic chuck, mounted on the 

 top of the drive rod and operated either hydraulically or mechanically. 

 This type of chuck permits chucking or unchucking the drill pipe without 

 stopping its rotation and thus saves some time and labor. 



The drive rod is fed downward, thus applying pressure on the bit at the 

 bottom of the string of pipe by means of two hydraulic rams (K) which 

 are attached to the drive rod by the yoke (P). The length of travel of this 

 hydraulic feed is usually 30". After each 30'' advance, the set screws in 

 the chuck are loosened, the hydraulic feed reversed to raise the chuck to its 

 top position, the set screws are again tightened, and the process is repeated. 



The entire hydraulic system operates on a closed circuit using a light 

 hydraulic oil as the fluid, and it is completely independent of the mud pump 

 circuit. The system includes the hydraulic pump (usually a vane type 



