220 ] ounial of Agriculture. Victoria. [lo April, I9I2_ 



A drill (Fig. 56) is made to fit the socket of a machine or ratchet-brace 

 by forging ; the cutting end is first formed like a punch, then flattened 

 at the end as shown, and the corners cut off. The temper of a drill needs 

 to be dark straw at the point, which is slightly harder than the chisel. 



A cross-cut chisel (Fig. 57) is used for cutting key-ways in wheels that 

 are fixed to a revolving shaft ; or when it is necessary to remove a large- 

 amount of metal from a large flat surface the cross-cut is used for chipping a 

 number of grooves, and the ridges so left are cut off with a flat chisel. 

 The process of making a cross-cut needs but little description, the shape- 

 being suggestive of the mode of procedure. One point about it is that 

 the end of the chisel needs to be made wider than the remaining part of 

 the blade. If it is not widened out as shown in the drawing it will stick 

 in the groove formed by cutting, and so cause trouble. It is tempered in 

 exactly the same manner as the cold chise(. 



If a tool when put to use after forging and tempering is found to- 

 quickly blunt, it shows that the temper has been reduced too much. 

 In such a case, retemper it to a lighter colour, e.g., if it were tempered, say,. 



FIG. 54. COLD CHISEL. 



FIG. 55. rUNClI. 



FIG. 



FIG. 57. CROSS CUT CHISEL. 



to a purple hue, then let it be dark straw. It will further be found that 

 whilst one piece of steel will be sufficiently hard at purple, another will 

 require a higher temper — due to the quality of the steel. 



When a tool breaks in working, it may be through being tempered too 

 hard, or through overheating in forging or tempering. If from the first 

 cause the fracture will be quite white, and on examination of the fracture 

 it will be found to be of a very fine grain. When overheating has been the 

 cause then the break will be partly black and partly bright and the fracture 

 will be always curved; if badly burnt the break will show a very coarse 

 and cry.stalline grain. 



Pointing a Pick. 



Picks are made of iron, with a small piece of steel welded on to the- 

 point. This, of course, wears away, and necessarily requires to be relaid. 

 Sometimes only a very short piece of steel has been welded on, and when 

 such is the case a new piece may be welded on by splitting the end of the 

 pick with a hot chisel (so as to make it look like the letter Y), a piece of 

 steel first made wedge-shaped and inserted into the split ; a welding heat 



