To give to n sufficient rise and fall to enable it to grip or fall entirely free from the shears with the small amount of rotary motion which the handle-lever l is enabled from its position to have, the following device is provided. m is a washer interposed between l and b′′. This washer has upon it steps of different thickness as shown at m and m, the two thicknesses being formed by an incline as shown. The face of l has, as shown, similar steps; now as shown in the cut the step l on lever l meets the steps m of the washer, the handle having receded to the limit of its motion. The bolt k then has fallen to the amount due to unscrewing the threaded or nut end of l, and also to the amount of the difference of thickness at m and at m of the washer, the plate n being clear of the lathe-shears. But suppose the handle l be pulled towards the operator, then the surface l passing from a thin section on to a thick one as m of the washer, will lift the bolt k, causing n to meet the under surface of the shears, and then the motion of l continuing the pressure of the thread will bind or lock n to the bed.

The surface a′ in [Fig. 497] affords a shelf or table whereon tools, &c., may be placed instead of lying on the lathe bed, where they may cause or receive damage.

Fig. 498.

[Fig. 498] represents an end view of the tailstock viewed from the dead centre end, the same letters of reference applying to like parts that are shown in [Fig. 497]. The split at f is here shown to be filled with a piece of soft wood which prevents the ingress of dust, &c. At d is a cup or receptacle for oil, e being a stopper, having attached to it a wire pin flattened and of barb shape at the end, the object being to cause the wire to withdraw from the cup a drop of oil to lubricate the dead centre and centre in the work. The proximity of e to the dead centre makes this a great convenience, while the device uses much less oil than would be used by an oil can.

The method of setting over the upper part b to enable the turning of the diameter of work conical or taper instead of parallel is shown in [Fig. 498]: p and p′ are square-headed screws threaded into the walls of a and meeting at their ends the surface of b′. In a there is at a a wide groove or way, and on b there is at b a projection fitting into the way a so as to guide b when it slides across a, as it will when p is unscrewed in a and p′ is screwed into a. This operation is termed setting over the tailstock, and its effect is as follows:—Suppose it be required to turn a piece of work of smaller diameter at the end which runs on the dead centre, then, by operating the screw p towards the front of the lathe (or to the left as shown in the cut) and screwing p′ farther into a, the end of p′ will meet the surface of b′, causing b′ to move over, and the centre of the dead centre j (which is the axis of rotation of the work at that end) will be nearer to the point of the cutting tool. Or suppose the work requires to be turned a taper having its largest diameter at the end running on the dead centre, then p′ would be unscrewed and p screwed farther into a, carrying b farther towards the back of the lathe.

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