An easy method of dividing plates of hardened steel, such as saw plates; and also of perforating them, when requisite.
Workmen frequently wish to divide a broken saw plate, for the purpose of converting it into scrapers, square-blades, or small saws; this is usually attempted by notching them to a small depth with a cold chisel, and then breaking them along the lines so made. When the plate is very hard, this method will not succeed, and the plate is frequently destroyed in the attempt. When it does succeed, the plate is generally twisted, and buckled, in the operation.
The Editor had a hard plate, which he was desirous of cutting into strips, to make small saws for a working model of a saw mill; this, although too hard to yield to the chisel, he divided with the utmost facility, piercing the ends at the same time, for the purpose of stretching the saws; this was effected in the following manner.
The saw plate was made sufficiently warm to melt bees-wax, which was then rubbed over it, so as to coat it completely on both sides, when it was suffered to cool. Lines were then drawn through the wax on both sides of the plate, with a steel point. It being of great importance that these lines should be exactly opposite to each other, this was effected by making a saw-kerf in the strip of wood which was used as a straight-edge, and the plate being placed in the kerf, the opposite lines were easily drawn. A mixture of sulphuric acid (oil of vitriol) and water had been prepared, and suffered to become cold; the proportions about one part of acid to six of water.
The sawplate was then placed in a common queens-ware dish, sufficiently large to contain it within the rim, and the acid and water were poured into it, so as just to cover the saw-plate; in about half an hour it was taken out, washed in clean water, and the wax scraped off, the lines having been bitten in to a sufficient depth to cause the plate to break with great ease. Some pieces which were left in too long, were eaten, quite through, and the edges rendered rough and indented by the action of the acid.
At the ends of the plates, where holes were wanted, the wax was removed on each side; it was found necessary, sometimes, to insert these ends in the fluid, longer than the time allowed for the action on the lines; this, however, depends upon the thickness of the plate.
Circular saws may be readily made in this way, and their centres perforated to any size. Square or round holes may be made through a plate of one-fourth of an inch in thickness without the slightest difficulty. To effect this, after covering the part with wax, and scratching through it, in the way directed, a wall, or bank, of wax is to be placed round it, so as to form a cup, into which the liquid may be poured; this operation must be repeated on the opposite side, and when the lines are bitten to a good depth, the piece may be punched out.
Whenever the plate to be divided, or perforated, is large, a bank of wax may be made to surround the parts, or the acid and water may be repeatedly washed over the lines, until the corrosion is sufficiently deep.
Care should be taken to employ good, clean wax; for the acid will find its way through it wherever there are any specks of dirt, and thus injure the face of the plate. Engravers’ etching ground would be a better article than wax, but the latter is easily obtained, and, if pure and clean, will answer very well.
Saws and other tools of iron or steel, may be readily marked with the name of the owner of them, by the foregoing process.
By the Editor
The Franklin Journal and American Mechanics’ Magazine
Vol. III.—No. 3.—March, 1827
– Jeff Burks