When making fluid dies the two halves are machined exactly the same height, and the faces that come in contact with each other when the dies are together must be at right angles with the bottom. The two pieces are either screwed to a plate or attached to a special holder so that one half can be removed and replaced and the plate strapped to the faceplate of a lathe. A fine prickpunch mark is placed exactly on the line where the two halves meet and the prickpunch mark should be in the center of the two halves. If the prickpunch mark is indicated true, the hole will have half its diameter in each half of the die block; otherwise, one half will be of a greater diameter and trouble will be experienced in removal of the formed cup. The stock is removed in the usual way by spotting with a flat spotting tool, Fig. 61, rigidly held in the tool post to insure the spot being true, as the spotting tool actually bores or turns the recess spot which is to be the starting point for the drill that removes the stock. The angle of the spotting tool and the drill should be the same.
Fig. 61. Cutting Tool Used for Fluid Die.
Good results cannot be obtained by holding an ordinary drill in a chuck in the spindle of the tailstock of a lathe as there is too much spring due to play between the spindle and the hole of the tailstock, and due also to the spring of the drill, chuck jaws, and spindle of the tailstock, which is greatly increased as the distance from the point of the drill to the tailstock is increased. A mark, or a piece of wire is placed on the drill the desired distance from the point of the drill to act as a guide for the depth to be drilled. If the drill is too large to enter the tailstock chuck, a dog may be fastened to the shank of the drill, using a thin piece of sheet brass between the drill and the dog to prevent marring the drill, and, by placing the center of the tailstock in the center of the drill and allowing the tail of the dog to bear on the seat of the tool post, the hole can be drilled.
A tool should be fastened securely in the tool post of the lathe and the tail of the dog should just touch the tool when the center of the tailstock is bearing on the drill center, and as the drill is fed into the work the carriage of lathe should also be moved along at exactly the same rate of speed, always keeping the tail of the dog bearing against the tool and also bearing on the seat of the tool post. If this is not done, the drill is likely to draw in, especially so if the drill passes clear through the work, and, as the drill catches or draws in, the center of the drill is pulled away from the lathe center in the tailstock, and the drill then rotates with the work. The object of having the tail of the dog bearing against the tool in the tool post is to enable the die-maker to hold the drill on the center of the tailstock. Under no circumstances should the dog be held by hand, either when drilling, or when removing the drill, while the lathe is rotating. The pressure and blow of the tail of the dog when a 1-inch drill catches in the work is sufficient to crush a hand or to sever a finger. Many fingers are lost in this manner.
It is appropriate to mention the danger when attempting to hold work by hand in drilling with a drill press. Always bolt the work to the table if the work is large or thin, or hold the work against a rigid stop on the drill-press table, and if the work is small it can be held in a large clamp or wrench. Thin work catches on a drill more often than heavy pieces, due to the point of the drill passing through the work before the body of the drill enters, and the work will run up the spiral of the drill to the end of the spiral, then rotate with drill. At times the work simply tilts at an angle and instantly assumes the same number of revolutions as the drill, and severe lacerations are the result if work is held by hand. The writer once had a ¾-inch drill catch in a drop-forge die block that weighed 112 pounds and the block was whirled, nearly upsetting the drill press, and finally the drill broke and the block was hurled some distance from the press. Emphasize again the tool-makers' slogan - "eliminate all chances".
Having drilled the hole in the fluid die to proper depth, the form is now bored. This involves the use of a blanked piece of steel,/, Fig. 58, that was previously turned the exact shape desired or rather the shape of the desired cup. By using formed boring tools the impression in the die is made to absolutely fit piece / when the dies are closed. As the larger diameter of the die is blind, that is, cannot be seen when boring, the shape is determined by placing an even light coating of Prussian blue on the model piece / and rotating piece / when the die halves are bearing against it. A streak or streaks of blue will show in the die and by moving the movable half of the die the die-maker is enabled to see the work and to set the boring tool so that it will cut exactly on the streak of blue paint. This type of lathe work requires patience and skill, and several specially made boring tools of different radii.
Another way in which this type of die can be made is to bore the die as above, almost to size and shape, and to finish the die in a drill press by having the model / of tool steel with teeth cut in it, g, Fig. 58, as in a formed milling cutter. The formed cutter, which is called a cherry, is hardened, and is gripped in a drill-press chuck, and the dies closed on the cherry. As the cherry revolves, the two halves which are held between clamps are closed onto the cherry, which cuts the desired form. The drill press must be stopped frequently and the clamp removed and the chips cleaned from the cherry, as there is no chip escape; plenty of oil should be used. If the design of die is not too intricate, however, the lathe method is quicker and in most cases better.
Having obtained the desired shape in the die halves, the next operation is to cut the design. It is obvious that the hob method cannot be used in a die made in halves, as the design on a, Fig. 58, encircles the blank, and, if a hob were made having the design extending the entire circumference, the action of the hob when closing the two halves on it would be that the raised figures on the hob would cut away the die halves in a straight line. Therefore, the design must be cut in by hand, and the design must also be laid out in the die halves the reverse of that desired on the finished cup.
There are several methods employed in transferring the outline of the design to the die. One method is to make a transferring roll, of material similar to printers' rolls and of the same shape but a trifle smaller in diameter than the bored portion of the die. The roll has a central hole its entire length, and larger in diameter at the top. The design is now sketched on a piece of thin paper which is exactly the same length as the circumference of that portion of the die having the figures, and after the design is accepted the lines of the design are inked, using slow drying printer's ink, and the paper strip is pressed into a straight piece of wood which has been grooved the same shape as the contour of the die and the composition roll, as in Fig. 62. By rotating the composition roll from one end of the paper to the other the ink is picked up on the roll. Then, by cleaning the die thoroughly and placing the composition roll in the die and forcing a round plug in the small hole in the composition roll, the roll is expanded to fit the die and the ink from the roll is transferred to the die. This method only gives the general design and its location, as the ink will spread somewhat. With an engraver's point, which is a fine oil stone in the form of a lead pencil, or with a sharp scriber, the outline of the design is scratched in the die.
Fig. 62. Rolling Die with Composition Roll.
From now on the work is strictly die-sinking and engraving, using small curved cold chisels to remove the bulk of the steel, shaping with engraving tools of various shapes, and lastly smoothing with files and wood stick with emery.
Die-sinker's wax is used for proving, and by smoking the surface of the die and forcing in the wax the impression as it should be on the cup is formed in the wax. The wax should be examined closely to find if any portion of the figure of the design is distorted, for an undercut on any part of the design will prevent the cup from being removed after being forced into the die.