Fig. 1165.
Fig. 1166.
The method to be employed for centring work depends upon its diameter, and upon whether its ends are square or not. When the pieces are cut from a rod or bar in a cutting-off machine, the ends are square, and they may be utilized to set the work by in centring it. Thus, in [Fig. 1165] is a top, and in [Fig. 1166] is an end view of a simple device, or lathe attachment for centre drilling. s is a stand bolted to the lathe shears and carrying two pins p, which act as guides to the cup chuck or work guide g; between the heads of pins p and the hubs of g are spiral springs, forcing it forward, but permitting it to advance over the drill chuck; the work w is fed forward to the drill. At the dead centre end the work is supported by a female cone centre d in the tail spindle t. The work rests in mouths of g and d, and as the pieces are cut from the rod they are sufficiently straight, and being cut off in a cutting-off machine the ends are presumably square; hence the coned chucks will hold them sufficiently true with the ends, and the alignment of the centre drilled holes will not be impaired by any subsequent straightening processes; for it is to be observed, that if work is centre-drilled and straightened afterwards, the straightening throws the centre holes out of line one with the other, and the work will be more liable to gradually run out of true as its centres wear.
Fig. 1167.
