126 BULLETIN 711, U. S. DEPARTMENT OF AGEICULTUEE. 



The main engine, or what is known as the skidding engine, has 

 12 by 12 inch cylinders and three drums. The back drum, the one 

 next* to the boilers, is known as the slddding line drum. This drum 

 hauls the log in. The middle drum is known as the return or trip 

 line drum. This is used not only to haul the carriage back to the 

 woods but to hold the carriage in proper position when the log is being 

 yarded under the carriage, also to regulate the speed of travel of the 

 load when gravity carries it forward. The return line drum is pro- 

 vided with an interlocking and reversing device, which permits the 

 interlocking of the skidder and receding line drum after the ends of 

 the logs have been elevated sufficiently to clear obstructions. By 

 means of this device the return line is paid out automatically as the 

 skidding line is drawn in. The third drum from the boiler is the 

 slack-pulling drum, which enables the engineer to pay out from the 

 carriage the length of skidding line that is necessary to reach the logs 

 that lie to one side or the other of the overhead cable. The slack- 



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Fig. 40. — Skidding carriage, Lidgerwood overhead system. 



pulling drum has a friction device set with a tension of about 500 

 pounds, so that the line will not hang slack. 



The loading engine has double cylinders and four drums, two 

 friction and two clutch drums. The friction drums are used in 

 loading, but only one of them at a time. The two make it possible 

 to shift the loading line from one side to the other, so that it is unnec- 

 essary for the loading engineer to look over the machine when loading 

 is in progress. The two clutch drums are used for raising the main 

 cable, rigging, etc. 



The machine, as a rule, is mounted on a steel car, which is 22 by 8 

 feet and is equipped with a jack at each corner and swivel trucks. 

 With this equipment it is possible to jack up the car, turn the trucks, 

 lay short pieces of steel rail under the car wheels at right angles to 

 the track, and move the car from the track. 



The skidder may be mounted on a sled ; in fact, some operators find 

 it suits their purpose best to mount it this way. No other method 

 could be used where it is necessary to place the skidder at some point 

 other than along the track. 



