Mechanics: The Science of Machinery

by A. Russell Bond

HELPING THE FARMER

THE FIRST efforts at directing the forces of nature and employing them in the service of man were made by the farmer. The task of growing food was quite the most important of primitive occupations, and although the virgin soil was rich and the yield abundant there were regions where crops could not be raised except at the expense of constant toil. Infrequent rains made it necessary to carry water by hand from wells and rivers and pour it over thirsty lands. As the grain fields grew more extensive, irrigating ditches were used which saved the toil of carrying the water, although it still had to be raised by hand. Then machines were invented by which water could be raised by animal power and, finally, as we have already seen, automatic water-lifting machines were constructed by which the river itself was constrained to lift a part of itself and pour this part into the irrigation ditches.

While it is true that the earliest machines were built to lighten the work of the farmer, the attention of inventors was soon attracted to other fields of endeavor and the farmer was left to toil slavishly from daybreak to sundown with no further mechanical aid. The tools he used were improved in form and quality. Oxen were used to draw the plow. The wooden plow made out of a forked stick gave way to a bronze plow and, finally, to one of iron. The curved knife or sickle went through a similar process of evolution from flint to iron. It was the only implement used for cutting the standing grain, and not until comparatively recent times did it give way to the scythe. Practically all the work of tilling, seeding, cultivating, harvesting and threshing was done by hand in practically the same way and with practically the same tools from the time of the Pharaohs down to the end of the eighteenth century.

THE FIRST HARVESTING MACHINE

To be sure, there is a record of a harvesting machine built in Gaul, while that province was under Roman dominion. Pliny described this machine in 70 A. D. It consisted of an ox cart which was pushed through a field of grain, instead of being pulled by the ox. This cart carried a rack or comb which caught the heads of the standing grain, tearing them off and delivering them into the body of the cart. Unfortunately this primitive, but useful, harvester was not extensively employed and in time it was lost to agriculture. Farmers reverted to the time-honored method of reaping by hand and the ox-pushed machine was forgotten. From time to time in recent years this machine has been reinvented and a machine similar in principle is used to-day to gather clover seed.

The scythe was a distinct improvement over the sickle. It enabled a man to use two hands at the work of reaping instead of one. It provided a much longer and heavier blade, and hence a much broader swath was cut at each stroke. A distinctly American improvement on the scythe is the grain cradle, consisting of a set of fingers above the blade which catch the grain and lay it in a swath at the end of the stroke. This important improvement rapidly spread to all parts of the world and is still used to-day where it is impracticable to use a mechanical reaper. It is claimed that one man can cut and bind more grain with the cradle than three men could with the sickle.

EVOLUTION OF THE PLOW

The plow has undergone important developments in comparatively recent years. Wooden plows were still in use in America in Revolutionary times; usually the point was shod with wrought iron. However, these wooden plows speedily gave way to metal when iron came to be manufactured in considerable quantity in this country. A plow has to contend with two conditions of service that apparently conflict with each other. The constant friction of the soil against the blade tends to wear it away very rapidly, hence a very hard surface is requisite. On the other hand, the plow is apt to encounter buried stones and rocks which will shatter it unless it is soft. The problem then is to make the plow both hard and soft. The chilled iron plow was invented by Oliver, in 1855, to meet the first condition. When molten iron is poured into an iron mold the surface that comes into contact with the mold is suddenly chilled, producing a very hard surface that takes a good polish. This effect is accentuated by using a hollow mold through which water is circulated. The hard surface of the chilled iron wears well in sandy and gravelly soil, it does not rust deeply, and it clears well in sticky soil. However, it is very brittle and is liable to break if struck a sharp blow. A more recent improvement is the soft-center steel plow. This is both hard and soft. It is composed of three layers of metal; the outer layers are of hard cast steel and the center one of soft steel. These metal layers are heated to a welding heat and then rolled together, producing a plow that has a hard outer wearing surface and at the same time is tough because the center layer of soft steel acts as a cushion to absorb sharp blows. To increase the wearing qualities of the plow still further a patch of very hard cast steel is welded over the point of the share. Thus both conflicting requirements of softness and extreme hardness are met.

We think of the plow as a very simple tool, but the modern implement is a product resulting from a vast amount of study and research into the materials most suitable for its construction and into the best form of share and moldboard. In place of a single plow for all purposes the modern farmer is offered a large assortment to suit various classes of work. At least three different kinds of plows are indispensable on every farm; the sod plow, the stubble plow, and the corn-cultivating plow. The sod plow is used for turning over the sod and breaking the clod. This is provided with a jointer or diminutive plow point set above the share, which turns over the edge of the furrow to prevent grass from growing up between the furrows. The stubble plow has a moldboard with less twist than that of the sod plow. This is used for plowing land that was under cultivation during the previous year.

The plow of to-day has become more than a hand-guided, horse-drawn tool. It has developed into a real machine, mounted on wheels, with a disk or coulter wheel that cuts the furrow cleanly, means for leveling the plow and regulating the depth of the plow, and a seat for the plowman. It works upon soil with the same precision that a planer works upon a slab of cast iron. The furrow is neatly sliced, lifted, and turned over with mechanical accuracy. As the furrow slice slides over the moldboard of the plow the soil is pulverized by friction. The front furrow wheel runs in the furrow previously cut which serves as a track to guide the machine. The front and rear furrow wheels are inclined from the vertical so as to balance the thrust of the plow and they may be given a lead toward or from the “land” or unplowed part of the ground to regulate the steering automatically. The proper adjustment and balancing of a plow calls for considerable skill.