After theremarks offered on pages 919to 923, on shearing tools, little remains to he said in this place on the punching machinery used by engineers, as it was there stated that the cutters for shearing and the punches, were most usually combined in the same machine; the punch being placed either at the outer extremity of the jointed lever, or at the bottom of the slide in those machines having rectilinear action. The punch is fixed to the slide or moving piece, the die is secured to the framing by means of four holding and adjusting screws just as in fly-presses, and the puller-off or stop is likewise added, all which details are represented in the woodcuts on pages 920 and 922.
The principal application of the engineer's punching engine, is for making the rivet-holes around the edges of the plates of which steam-boilers, tanks and iron ships are composed. Another important use, and in which the punches trench upon the office of the shears, is in cutting out curvilinear parts and apertures or panels in boiler work, to which straight-bladed shears cannot be applied. In this case the round punch is used in making a series of holes running into one another, along the particular line to be sheared through, or in other words the punch is used as a gouge, by which the hole that has been first formed, is extended by cutting away crescent-form pieces, thus leading the incision in any required direction.
This employment of the punch to shearing curved lines, is also much used in cutting out the side plates of the framings of locomotive engines, which consists of two pieces of stout boiler plate, (the technical name for iron in sheets from 1/4 to 3/4 inch thick,) riveted alongside a central piece of wood, that is sometimes also covered above and below with iron, all the parts being united by rivets. The punching engine serves admirably for cutting out all the curved lines in these side plates, also the spaces where the bearings for the wheels are situated, and various apertures.
Messrs. Maudslay Sons & Field introduced, many years back, a very great improvement in the punching engine, as applied to making boilers and tanks, in which the rivet-holes are usually required to be made in straight lines, and at exactly equal distances, so that holes in two pieces punched separately may exactly correspond.
maudslay's punching machinery, experiments, etc. 951
The plate was fixed down upon a long rectilinear slide or Carriage, and during every ascent of the punch, was advanced by the machine itself, the interval from hole to hole, the moment after the punch was disengaged from the work. Subsequently, 2, 3, or 4 punches were fixed at equal distances in the vertical slide, but the punches were made of unequal lengths, so that they came successively into action, thereby dividing the strain, and the horizontal slide was consequently shifted every time a distance equal to 2, 3, or 4 intervals. This machine, which displayed much ingenuity of invention, served as the foundation of the more simple punching engines that are now met with.*
This volume will be concluded by the account of two sets of experiments in punching. The first "An account of some experiments to determine the force necessary to punch holes through plates of wrought iron and copper by Joseph Colthurst." †
"These experiments were performed with a cast iron lever, 11 feet long, multiplying the strain ten times, with a screw adjustment at the head, and a counterpoise." - "The sheets of iron and copper which were experimented upon, were placed between two perforated steel plates, and the punch, the nipple of which was perfectly flat on the face, being inserted into a hole in the upper plate was driven through by the pressure of the lever."
"The average results of the several experiments (which are given in a detailed tabular form), show that the power required to force a punch half an inch diameter through copper and iron plates is as follows:
* Mean. Maudslay contrived their machine, in order to manufacture in a abort space of time, a very considerable number of water tanks for the Royal Nary; the machine is carefully engraved in platee 51 and 52 of Buchanan's Treatise on Mill Work, edited by G. Rennie, Esq., F.R.S.
Other punching engines, some of them with shears, are also engraved on pages 48, 50, and 52* of the same valuable work.
The plate 52* contains the section and elevation of a steam punching machine by Mr. Care, of Paris; it is in effect a combination of the punching machine with the high pressure steam engine. This machine may carry either punches or shearing cutters at pleasure, but although apparently more costly than those actuated as usual by a simple crank movement, it does not appear to be so convenient, neither would it be politic to construct every machine in a factory, so as to include a steam engine for its own especial use.
† Extracted from the Minutes of Proceedings of the Institution of Civil Engineers for 1841, pages 60-1.
952 coulthurst's and hick's experiments in punching.
0.08 thick, required a pressure of
"Hence it is evident, that the force necessary to punch holes of different diameters through metal of various thicknesses, is directly as the diameter of the holes and the thickness of the metal. A simple rule for determining the force required for punching may be thus deduced. Taking one inch diameter and one inch in thickness as the units of calculation, it is shown that 150.00 is the constant number for wrought-iron plates, and 96.000 for copper plates. Multiply the constant number by the diameter in inches, and by the thickness in inches; the product is the pressure in pounds, that will be required to punch a hole of a given diameter through a plate of a given thickness."
"It was observed that the duration of pressure lessened considerably the ultimate force necessary to punch through metal, and that the use of oil on the punch reduced the pressure about 8 per cent."A drawing of the experimental lever and apparatus accompanied the communication.
The second experiments were by Mr. Hick, of Bolton, who by means of a hydrostatic press having four cylinders in combination, punched through various pieces of iron; the thickest of them measured 3 1/2 inches thick, and from which was punched out a disk of 8 inches diameter, with a pressure of 2000 tons.
The removed piece was rather thinner than the remainder and a little taper, which arose from the circumstance of the bolster having been purposely made with a flat bottom, and a little larger in diameter than the punch, so that the disk when removed was a little spread or flattened out.
It is curious that experiments so distant from one another in their scale of proportion, should yet agree so nearly; by Mr. Colthurst's formula
The computed force is . .
The actual force was . . .