Cutting tools worked by hand and machine by Robert Henry Smith

Author:Robert Henry Smith
Language: eng
Format: epub, pdf
Published: 1882-03-25T05:00:00+00:00

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not wear evenly during the subsequent turning. The position of the centre will gradually shift, and it will be found impossible to produce perfectly true work.

The centring machine above mentioned finds the true exact centre of the rough surface mechanically. The end of the bar is placed in a concentric chuck with four jaws, and these are screwed down upon it simultaneously. The centring drill, which is made to run exactly true with the jaws of the chuck, is then brought forward, and bores the hole without possibility of error in the exact centre of the largest circle that can be turned on the part gripped in the jaws of the chuck. In the case of bar iron, the ends are the important parts to get well centred. If when these are exactly true other parts of the bar are found to run untruly, they are to be corrected by bending the bar by striking it with a hammer on an anvil or some other solid resisting surfaca The centring machine is not, however, applicable to pieces of large size. In the turning of shafting and spindles of all sizes it is a very valuable tool.

15. The mode of driving the work when it is placed between the centres, and other methods of fastening it in the lathe, will be presently described.

16. Parallel and Conical Bearings in Headstocks. —In Fig. 34, A and c, it will be seen that the mandril of the fast headstock runs in parallel brass bearings. These brasses are split horizontally, and the upper halves are held down by cast-iron caps, bolted to the standards of the headstock by studs and nuts. As wear occurs, these can be tightened up by screwing down the nuts. The end-pressure due to the traverse feed is partly delivered by a collar on the mandril to the face of the right-hand pair of brasses. The greater portion of this axial pressure is intended, however, to be borne at the left-hand end of the mandril. In the sectional plan c are seen two horizontally placed pillaret studs attached to the left-

CUTTINO TOOLS.

hand standard of the head-stock, and both at the level of the mandril centre. Across the extremities of these is bolted a waall cftst-iroti bridge. The mandril thrusts upon this bridge through the intervention of a steel pin that is passed through it and is placed so that its centre-line is a coutinuation of that of the mandril. This bearing-pin has its ends screwed, and is clamped by two nute, one on each side of the bridge. B7 turaing these nuts in either direction, the pin can

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