LOGGING IN THE DOUGLAS FIR REGION. 



75 



them are frequently far beyond their normal capacity. To see them 

 hauling logs larger than 10 feet in diameter and 24 feet in length 

 over rough ground on a "straight" line is to marvel that they are 

 not wrecked in a short time. That they are not is due to the fact 

 that they are simply, compactly, and pov^erfully built of the best 

 adapted material. The frame or bed of the machine, on which the 

 security of all fastenings and the permanency of alignments of all 

 Avorking parts depend, is strong and rigid, being made of the heaviest 

 standard section of steel beams spaced by heavy crossbars of cast iron 

 or steel. 



Fig. 30.— Compound-geared yarding engine. 



Logging engines are equipped with high-pressure boilers of the 

 vertical type, built of 60,000-pound flange steel. They have a work- 

 ing pressure of from 150 to 200 pounds (generally 200 pounds), and 

 are guaranteed to pass Hartford inspection. They range in size from 

 48 inches in diameter and 96 inches in height to SO inches in diameter 

 and 153 inches in. height. 



The extreme height and high working pressure of these boilers, the 

 limits of which have been reached, is the result of constant increase 

 in the cylinder sizes. The width of the engine frame, by limiting 

 the diameter of the boiler, has restricted the dimensions of the round 

 fire box, resulting in too small a proportion of grate to heating sur- 

 face. To overcome the steaming difficulties resulting from insuffi- 



