FIG. 4–41. Types of screw points, lag and cap screws.
Cap screws (Fig. 4–42) may have square, hexagonal, flat, or button types of heads. Such screws resemble closely a machine bolt with the exception that they do not have a nut on the threaded end; instead, the end passes through whatever it is to hold into a threaded hole which serves as a nut, for example, the cylinder head of an automobile.
Lag screws (Fig. 4–41) have heads like a machine bolt, while the other end is sharp. The threads are coarse and similar to an ordinary wood screw. They are used to attach machinery to floors or beams. The coarse threads, when started, will draw themselves into the wood as the screw is turned with a wrench.
FIG. 4–42. Types of screws: A, wood; B, machine; C, self-threading or tapping; D, cap.
Wood screws, unlike lag screws, are rather small and have slots across the head so that a screw driver can be used to force them into the wood. (Fig. 4–42).
Washers. Different kinds of washers are used extensively in connection with bolts in farm machinery. They may be used on either the end beneath the head of the bolt or beneath the nut. Washers are of various kinds as follows: flat malleable-iron, cast-iron, wrought-iron, and spring-lock washers. There is very little difference between malleable- and cast-iron washers, both being rather thick, oftentimes 1/2 inch, and placed where there is a considerable amount of wear. Wrought-iron washers are round discs with holes in the center to allow their being placed under the nut. Lock washers are made of spring steel with one side split from the edge to center of the hole. The ends of the split parts are turned in such a manner that they will allow a nut to be turned down easily but resist any effort to turn it off. A quick-repair washer is shown in Fig. 4–44.
FIG. 4–43. Hollow-head setscrew and wrench.
FIG. 4–44. Quick-repair washers: A, side-latch; B, over-latch.
FIG. 4–45. Types of springs.
Springs. Springs (Fig. 4–45) play an important part in the operation of farm machinery. Extension springs aid in lifting and adjusting heavy implements. Compression and torsion springs facilitate the operation of certain parts of a machine.
REFERENCES
Confer, L. J.: Standards for V-belt Drives on Farm Equipment, Agr. Engin., 31(5):237, 1950.
Curtis, George W.: Tapered Roller Bearings Practice in Current Farm Machinery Applications, Agr. Engin., 30(6):285–293, 1949.
Hansen, Merlin: Load Imposed on Power Take-off Shafts by Farm Machines, Agr. Engin., 33(2):67–69, 1952.
Kimmich, E. G., and W. Q. Roseler: Variable-speed V-belt Drives for Farm Machines, Agr. Engin., 31(7):334–336, 1950.
Potgieter, Fred M.: Application of Universal Joints to Farm Machinery, Agr. Engin., 33(1):21–27, 1952.
Rhodes, E. M.: Roller Chain Applications for Farm Machines, Agr. Engin., 31(1):19–20, 1950.
Virtue, Byron T.: Application of Needle Bearings in Farm Machines, Agr. Engin., 30(5):229–232, 1949.
Wolf, Lloyd J.: The Hydraulic Types of Variable-speed Unit, Agr. Engin., 31(12):615–617, 1950.
QUESTIONS AND PROBLEMS
1. Enumerate the various methods of transmitting power in farm equipment. (a) Explain the merits of each method. (b) Explain the difference between a direct and a flexible shaft drive.
2. (a) Explain how the sizes of V belts are designated. (b) How is the pitch length designated? (c) Explain what is meant by a double-sided V belt.
3. The centers of two B-type V-belt sheaves are 24 inches apart. The drive sheave has a pitch diameter of 14 inches while the driven sheave has a pitch diameter of 5 inches. Find the length of V belt required. Take into consideration the installation take-up allowance.
4. Explain the differences between and the uses of (a) single sheave; (b), multiple sheave; (c) variable-speed sheave.
5. Under what conditions are the following used: (a) hook-link chain; (b) roller chain?
6. Enumerate the various types of gears and explain their special uses.
7. A tractor is used to operate the horizontal-rotating knives of a stalk cutter-shredder. The tractor power-take-off runs at 560 r.p.m. and drives a pinion gear with thirteen teeth. The driven gear has 24 teeth. (a) Find the r.p.m. of the knife blades. (b) Find the peripheral travel of the blade ends when cutting a circular pattern 57 inches in diameter.
8. Explain the functions of the universal joints in a power-take-off drive. What is the accepted standard size of a power-take-off shaft for tractors?
9. Explain the differences between the various types of clutches.
10. Explain the differences between and uses of the various types of bearings.
11. Enumerate the types of bolts, nuts, and screws.
1 ASAE-SAE Standard, 1944.
1 Power Take-off for Farm Tractors, Agr. Engin. Yearbook, 1954.
CHAPTER 5
LUBRICANTS AND LUBRICATION
Probably the chief cause for machinery wearing out is improper and insufficient lubrication. Much of this trouble can be traced to the negligence of the operator, the poor construction of bearings, and the failure to provide adequate means of conducting the lubricant to the bearing units. Lubrication is needed because of friction.
Friction. Friction is that force which acts between two bodies at their surface of contact so as to resist the sliding of one body on another. When one object is being dragged along upon another object, friction between the two tends to stop the one that is being dragged. When one surface rests upon another, there is a tendency for the inequalities of the one to fit into