Flat jig, or guide.
The modern designer of tools, implements and machines takes care that the parts upon which wear chiefly comes are easily removable so as to be cheaply replaced. A worn out plowshare is renewed for a dollar or two, keeping the plow as a whole substantially new. Should the pinion of a watch be destroyed by accident, it is duplicated from Waltham or Elgin for a few cents.
To-day rods, wires, screws, bolts, tubes, nails, sheets of metal, are made in standard sizes. Much the same is true of rails for railroads, girders, eye-bars for bridges, and the like. Thus the product of any factory or mill may be used to piece out or to repair work turned out by any other similar concern. Yet more, if a subway or a tunnel is to be built in a hurry, two or more steel-works may co-operate in furnishing beams, columns, or aught else, with no departure from ordinary gauges. Steel works in Pennsylvania have produced every detail for a bridge erected in Africa, a factory in Germany, a stamp mill in Canada. At the World’s Congress of electricians held in Chicago in 1893, units were adopted as international standards, a noteworthy step toward adopting universal standards in all branches of engineering. Here progress is to some extent held back by firms and corporations that produce patterns not always worthy of defence. Standard forms and dimensions, especially in manufactures for a world-market, are only decided upon after thorough discussion, so that they are judiciously chosen. Among feasible shapes and sizes for rails, columns, girders, and the rest, one is usually best, or a few are best. Why not exhaust every reasonable means of ascertaining which these are for specific tasks that they may be freely chosen? Then if individuality prefers its own different designs, let it do so knowing what the indulgence costs.
A Test Shows How Concrete May be Cheaply Strengthened.
Measurements may be conducted in the strict spirit of scientific research, not immediately directed to industrial ends. Methods thus perfected are more and more being adopted for large questions of industry. Let an example be presented from the field, briefly touched upon in this book, of concrete as a material for the builder. Says Mr. C. H. Umstead of Washington, Pennsylvania:—
“Many thousands of tons of the finer grades of stones from the crushers all over the country are rejected by engineers for use in concrete foundations and walls, sand being preferred at greatly increased cost. I prepared seventy-two three-inch cubes with quartz sand and with varying proportions of crushed stone which was going to the dump as unfit for foundation work, and submitted them to crushing tests at periods of fourteen and twenty-eight days. The proportion of Portland cement was constant.”
From Mr. Umstead’s table of results the following figures are chosen; on comparing those for the first and third cubes they show that a gain in strength of forty-three per cent, followed upon using six pounds of crusher refuse instead of five and one half pounds of sand.
| Sand | Portland Cement | Water | Crushed Refuse | Compressive Strain | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 14 Days | 28 Days | |||||||||||||
| 8 | .5 | lbs. | 4.5 | lbs. | 1 | lb. | none | 2850 | lbs. | per | sq. in. | 3670 | ||
| 6 | „ | 4.5 | „ | 1 | lb. | 3 | lbs. | 3120 | „ | „ | „ | 5050 | ||
| 3 | „ | 4.5 | „ | 1 | .125 | lbs. | 6 | „ | 3620 | „ | „ | „ | 5250 | |
So much for the value of a test in the improvement of an important manufacture.