After machining the top surface of the shoe, the bushing is inserted. At this point is where the die-maker must be careful on this particular job. The haphazard trust-to-chance method is to drill and counterbore the hole for bushing, drive in the bushing, attach the stripper by means of screws, then put the hole in the stripper by transferring through the hole in the bushing.
The more accurate and workmanlike method is to make the punch after machining the top surface of the shoe, then to make and attach the stripper to the die shoe by screws and well fitting dowel pins. Lay out and prickpunch on the stripper face approximately the desired location for the die hole, and strap the die shoe to the faceplate of the lathe. It should be remembered that whenever any work is clamped to the faceplate of any machine, the faceplate with the work attached is always to be revolved one complete revolution by hand to make sure that projecting corners of the work clear all parts of the machine; this will prevent many accidents.
Indicate the prickpunch mark to be comparatively true. The shop phrase indicate means to place the contact point of a test indicator, as shown in Fig. 3, against the work, and, when the work is properly located, the indicating pointer will not deviate from a graduation on the arc. Graduations on test indicators are usually so spaced that their intervals represent one one-thousandth of an inch each. If the indicating pointer moves two graduations during one complete turn of revolving work, it means that the work is actually out of true only one one-thousandth.
Spot the stripper and drill the hole clear through both the stripper and the die shoe. Then bore the hole in the stripper to fit that portion of the punch that enters the stripper. The stripper is now removed, but the die shoe is not disturbed, and the hole for the bushing is bored in the die shoe to a driving fit. The reasons for boring the stripper are many. First, we can make the hole fit the punch, which would not be so easy if the hole in the stripper were drilled - the drill being guided by the hole in the die which would be somewhat larger than the drill. It is obvious that the hole in the stripper might not be directly in line with the hole in the bushing. Again, by drilling through the die shoe the shoe would rest either on the screw heads on the stripper, or on the face of the stripper, or on the parallels, any one of which may cause the drill to pass through the stripper on an angle. Granting that the parallels, or whatever is used, will insure the bottom of the die shoe resting parallel with the table of the drill press, it does not follow that the table of a much abused drill press is at right angles with the travel of the drill-press spindle, and the hole that is drilled and reamed through the stripper may be at an angle, so that when the die is set up for work in the press the punch will have to spring every time it passes through the stripper, which will eventually cause breakage of the punch.
Fig. 3. Various Positions of Ten Indicator in Shop Work Courtesy of L. S. Starrttt Company, AIM, Massachusetts.
It is attention to these apparently unimportant details that distinguishes the master workman from the ne'r-do-well class. At first glance, the punch and die shown in Fig. 306, Tool-Making, Part III, looks insignificant - all that is necessary apparently being simply to turn up a round piece, bore out a round hole, attach a strip across the top, and the die is complete - and on some classes of work this is true, but that same simple die may be called upon to perform work that requires greater care in die-making than the haphazard method.
Fig. 307, Tool-Making, Part III, shows that type of die known as an irregularly shaped blanking die. When making this die the die-maker should follow the blue print absolutely, unless, of course, he discovers an apparent mistake, in which case the foreman's attention should be called to the fact. If a blue print is furnished, the dimensions and the horizontal angle at which the die is to be laid out appear on the print, but if no drawing is furnished, the die-maker should first of all ascertain what width and what thickness of stock is ordered for the job, as the width of the stock governs the angle at which the die must be laid out on the die block.
The angle of the die in relation to the die block is very important, if the blank is to have subsequent bending operations, due to the fact that in rolling the sheet stock there is an actual grain, and bending the blank with or across the grain is almost analogous to bending wood. A piece of sheet stock can be bent at right angles having a sharp corner, if the bend comes crosswise of the grain, but if the bend is made lengthwise of the strip, the stock will break. Therefore, a die-maker, knowing this, should not proceed with a die unless he has full information. This is another instance of eliminating every element of chance or, that other bugaboo, of taking things for granted.
Assuming that the blank is to remain flat and that the sheet stock is ordered just wide enough to punch one blank from the strip, the first move is to select the die steel, for it is absolutely essential when hardening the die to know what brand of steel the die is made from. Some makes of tool steel are more expensive than others, and certain makes are made to harden in oil which prevents distortion to a great extent, while if the oil hardening steel were hardened in water, the die would crack. On plain dies, such as Fig. 4, any good grade of carbon steel which is lower in- cost will answer, as there are no delicate points on the die to distort or to present chances of cracking. If there is no distinguishing mark on the steel, it is best to cut a small piece from the bar, drill several holes in it, and use it as a test spiece, hardening it in water.