Having ascertained the brand of steel, the block is cut from the bar, and the first surface to be planed or milled should be the widest surface; this giving a broad bearing for the machined surface to rest against the solid jaw of the vise. The edge is next machined, then keeping the broad machined surface against the solid jaw, the block is turned so that the edge just machined rests on the bottom of the vise. We now have two machined surfaces resting on two machined surfaces of the vise, and the other edge is machined. A pair of parallels are placed on the bottom of the vise, and the broad finished surface is placed on the parallels, which causes the two machined edges to come in contact with the vise jaws. We now have three machined surfaces to position the block when machining the other broad surface. At least one end of the die block should be machined at right angles, or to use the shop term, machined square with the edges. The object in machining the end is to aid later in laying out.
Whichever side is to be used for the top or working face of the die should have at least 1/16 inch of stock removed, due to the fact that in hot rolling tool steel the outer surface becomes oxidized and is decarbonized to a certain extent, and, unless enough stock is removed to get under this burned surface, the die may cause trouble in hardening as the top surface may be soft in spots, in connection with which, if the die is rehardened in an attempt to obtain an entire hard surface, the repeated hardenings invariably produce cracks in the die. If a die, after the first hardening, should appear soft in spots, it would be better to draw the temper and to grind, say, 1/32 inch from the top surface in order to remove all burned metal. If the decarbonized surface caused the soft spots, the entire surface of the die would be hard after grinding, and rehardening would be unnecessary. Also, prior to laying out the die, the top surface of the die block should be machined very smooth and should be further smoothed with emery cloth. Instead of laying the grain one way when using emery cloth, it is better to polish with a circular motion, as lines scribed on the die are more pronounced over circular emery marks than over straight ones. When nicely smoothed the surface should not be touched, especially with the fingers, as grease marks interfere with the proper bluing of the surface.
Fig. 4. Drawing of Piece to Be Prepared.
Fig. 5. Scribing Center Lines on Block.
The block is now placed, polished side up, over a forge and heated slowly until a deep blue appears on the surface, at which point the color is set by quenching, preferably in oil. A scribed line is more pronounced on a blue surface than if a copper-sulphate blue-vitriol solution is used, and another objection to the coppered surface is that it peels off when drilling and filing the die, which removes the -scribed lines. The die block is now ready to lay out.
If a templet or model blank is furnished from which to make the die, then the clamp shown in Fig. 332, Tool-Making, Part III, is used to securely hold the templet on the face of the die block while the outline is traced with a fine sharp pointed scriber. If, however, a drawing, Fig. 4, of the piece is furnished, the first step is to scribe center lines on the block as in Fig. 5, in order to transfer the outline, as shown on the drawing, to the face of the die.
Fig. 6. Method of Scribing Center Lines.
Referring to the drawing, Fig. 4, we note that the overall length is 2 inches and the width is 1 inch. A fine prickpunch mark is placed at the intersection of the lines, the divider points are set 1 inch apart, and a section of a circle is scribed at each end as at a, Fig. 6, and, by again referring to the drawing, it is noted that the inside dimension is 1¾ inches. The dividers are set at one-half this - 7/8 inch - and the lines bb are scribed. The width being 1 inch, the dividers are set at ½ inch and the lines cc are scribed. The lines dd, ee, and ff are now scribed, using the surface gage or scratch block as at B, Fig. 6. This is why one end of the die block was machined at right angles to the edges when machining. A square can be used instead of the surface gage, but it is not quite as handy.
The angle lines are scribed by setting the protractor at 45 degrees and scribing along the blade, as at Fig. 7.
Fig. 7. Scribing Lines by Means of Protractor.