sumed in bearing friction and this in turn means greater wear of the components. It is imperative that the frame be of sufficient size and have strength enough to furnish a practically vibrationless bed for the engine and have room to support the engine, radiator, transmission mechanism, fuel tanks, and operators' platform. In order to obtain the strength that is desirable in frame construction the usual material employed is the merchant structural shapes in steel, such as I beams, angles or channels. These members usually extend from front to rear and join the axles and are commonly held together crosswise by other cross pieces which are well braced by liberal gussets or fish plates. The frame is one member that will rarely need replacing, therefore it is usually a builtup structure composed of members permanently fastened together by riveting. The frame should support the bearings to which the important members of the transmission and rear axle are fastened, and it is good practice to attach a sub-frame or inner frame of steel to the main frame for supporting the engine and related parts. Some manufacturers build up the frame of steel plates firmly riveted together and following bridge construction in that the area of the section is greatest at the point farthest away from the supports. Tractor frames are sometimes built up of two main castings, one at the front, the other at the rear, joined by channels or steel angles. The front casting serves as a point of attachment for the front axle, while the rear member is often employed to support the important shafts and bearings. Typical Frames Described.-A typical tractor frame from which the power plant and related parts has been removed is shown at Fig. 114. It will be seen that the frame proper is composed of steel channels, which are firmly attached together by bolts. A sub-frame is carried beneath the main frame and forms a support for the power plant. The important parts of the transmission mechanism are clearly shown as is the general construction of the front and rear wheels and steering mechanism. The frame shown at Fig. 115 is one from which the wheels have been removed and shows clearly the method of construction ordinarily followed on tractors of conventional design. The frame consists of two side members cambered in at the front at a point just forward of the steering gear, which are joined together by means of cross braces of steel channels, angles, and plain bar stock. The engine is located just forward of the intermediate drive gear and is arranged in such a way that this member meshes with a gear on the engine crank shaft. The change speed and reverse gearing are thoroughly encased and form a unit with the differential cross shaft, which carries the bull pinions which drive the rear wheels through the medium of the bull gears. The operator's platform and the drawbar to which the ploughs or other machinery are attached are also clearly shown at the rear end of the machine. The method of using a casting for the rear end of the tractor frame and the advantages of this construction are clearly illustrated at Fig. 116. It will be observed that the counter shaft and rear axle are carried in substantial cast frame members which are attached to the side channels very securely. As the boxes which serve as bearings for the counter shaft and rear axle form part of the same casting member it will be apparent that a very stiff construction that will prevent frame distortion is utilized to secure the advantages accruing from absolute alinement of driving and driven members. FIG. 115A.-Frame of the "Twin City 40" Gas Tractor Built of Standard Structural Shapes, Such as Angles and Channels Joined Together by Flat Bars and Braced by Plates. An Exceptionally Substantial Design Representative of Best Construction. The aver Why Three-point Support Is Needed. age traction engine is designed for rough service and is often operated under conditions where a more finely |