76 BULLETIX 711^ U. S. DEPAETMENT OF AGRICULTURE. 



cient grate area, most new logging engines are equipped \vith a fire 

 box which is oblong or elliptical in shape and extends about 2 feet 

 beyond the cylindrical portion of the boiler on the front side. This 

 design increases the grate area considerably without correspondingly 

 increasing the width of the engine frame. 



All of the engines are double — that is, have two cylinders. Ordi- 

 narily, logging engines are classified by the size of the cylinders, the 

 diameter being given first. A glance at Table 7 shows the range of 

 sizes. The engines are of the heavy-duty type, the valves and valve 

 gear differing with the make. 



Standard drmn engines have two drums, placed either tandem or 

 opposite, or nearly so. These rotate upon their shafts and are held 

 fast when pulling by means of frictions. Several types of frictions 

 are used. They are operated either by hand or steam, the steam 

 friction being particularly desirable on the larger engines. The 

 main, or hauling, drum is made of steel ; the trip drum, which car- 

 I'ies the trip, or return line, is made of semisteel. These engines can 

 be equipped with loading and straw-line drums, driven either by 

 their own gear or pinions or by a chain drive. In the case of the 

 simple-geared engine, the cut-steel gears of the main and trip drums 

 are driven by a cut-steel j)inion on the engine crank shaft. The trip 

 drum of the compound-geared engine is driven in a similar way. The 

 main drum in the latter type, however, is driven through a compound 

 train of gears by an internal or external gear, a second pinion keyed 

 on the trip-drum shaft driving the gear of the main-drum shaft. 



The standardization committee on logging engines of the Pacific 

 Logging Congress recommended that the following definitions and 

 formulas be adopted as standard : 



(a) Right and left hand sides of a logging engine. — "When standing at the 

 boiler end of the engine and facing out over the drum, that side of the machine 

 to the right is termed the right-hand side and that to the left is termed the 

 left-hand side. In general, the engine is operated from the right-hand side. 

 This is frequently called the " engineer's side." 



(&) Main and trip drums. — The main drum is the drum which is used to 

 haul in the load. Tliis is sometimes called the forward or the lower drum. 

 The drum which is used to return the main hauling line is the trip drum, also 

 called the haul-back drum. 



(c) Rope capacity. — The rope capacity of the main drum and trip drum must 

 bear a more or less definite relation. On road engines the trip-drum capacity 

 should be not less than twice the capacity of the main drum, and so far as 

 practicable there should be approximately sis or seven hundred feet of addi- 

 tional capacity on the trip drum. On yarding engines the capacity of the trii> 

 drum should be at least two and one-fourth times that of the main drum, and so 

 Car as practicably this ratio should be slightly increased. To find the di'um 

 capacity the following furniula is used: 



Capacity=CXLx^X^- 



