PRECISION TOOL MAKING 



379 



the die opening into its proper position with respect to the punch. 

 Also, after the tool is set there is the possibility, especially in the case 

 of the higher speed presses operating at about 300 strokes per minute, 

 of the die shifting during operation and resulting in the "shearing" 

 of the cutting edges of the die and punch. To overcome this difficulty 

 the liner pin type of construction illustrated in Fig. 1, and the sub- 

 press type shown in Figs. 2 and 3 are used in the better grade tools, 

 and especially where a very small clearance must be maintained 

 between the punch and die opening. In the former the arrangement 

 consists of two or more round guide rods or liner pins fastened in the 



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Fig. 4 — Sketches of typical piece parts requiring accurately built punches and dies 



bottom part of the tool and passing up through accurately bored 

 holes in the top part, thus insuring that both members are always in 

 their proper relative position. While the liner pin type of tool affords 

 a very satisfactory alignment in most cases, the sub-press type is the 

 better construction which, because of its "piston and cylinder" 

 design, insures a more positive alignment. This is illustrated in 

 Fig. 3. The plunger D, to which is attached the die iV, perforators L, 

 etc., slides in the bushing F in the housing G, and is therefore always 

 in alignment with the base and the punch attached to it. This type 

 of construction is followed largely where the part is small enough so 



