Metal Working Tools 



45 



die stock set, with taps. (Hart Manufacturing Co., Cleveland, 



Ohio.) Its contents enable threads to be cut, and holes to be 



tapped, of |, T 5 g, f, j 2 -:, and f" diameter. The cost is 2 i2s. 6d. 



Below J", screw plates may be used (see Fig. 35), and these 



FIG. 35. Screw plate with tap holes. 



should be accompanied by a set of " taps " to fit, or a set of 

 taps may be made from the screw plate. Screw plates may be 

 obtained containing square tap holes, for the tap heads, in 

 addition to the cutting devices, and may conveniently range 

 from YQ to |" in ^s. Such a plate costs about $s. 



Taps (Fig. 36), which cut threads on the inside of a hole, 

 are of two kinds, " taper " and 

 "plug." The taper tap is inserted 

 first, as it commences the cutting 

 evenly, and the work is completed 

 by passing the plug tap through if 

 necessary. The plug tap is useful 

 in tapping a hole of limited depth, 

 as its diameter is equal throughout, 

 and it cuts full threads immediately 

 on entering. Taps may be made 

 by obtaining a quantity of "silver 

 steel " or excellent quality tool steel, 

 softening in sawdust, turning down 

 to a suitable size, and cutting a thread 

 by means of the screw plate, to a 

 distance of say 2". The threaded 

 portion is then filed as though it 

 were intended to make a square 



prism, and some portions of the threads are thus removed. If 

 a plug tap is to be made, grooves must now be cut in this 

 flattened portion. 



If a taper tap is required, it must first be filed as accurately 



FIG. 36. Plug and taper taps. 



