hollow steel mandril, M, and for the remaining one-eighth to receive the spindle S. The mandril is fitted in front with a tapered centre, C, and behind with a screw nut, N. The centre is for carrying one end of the job to be operated upon by the turning tool, and the nut is for engaging the screwed part of the spindle S. On the back end of the spindle there is a collar, c (kept in position by a larger collar or guard, G, with small screws), and a hand-wheel, HW.* Consequently, by turning this wheel in M H.W MOVABLE HEADSTOCK FOR A COMMON LATHE. one direction the mandril and its centre are forced forward, and when moved in the opposite direction they are screwed backwards. To prevent the mandril turning round, it is fitted with a longitudinal slot on its underside, into which fits the flattened or rounded end of a small screw, s. A fixing stud, FS, with a handle, enables the mandril to be clamped to the head when it has been adjusted by the hand wheel and screwed spindle. Description of a Screw-cutting Lathe.-By the favour of Messrs. John Lang & Sons we are enabled to give a general view, with a complete set of reduced working drawings, carefully indexed to every detail, of the very strong and superior 6-inch centre screw-cutting lathe, lately presented to the Author's Electrical Engineering Laboratory and Engineering Workshop by Mr. Andrew Stewart, of Messrs. A. & J. Stewart, and Clydesdale. This lathe weighs, with all its chucks and supernumerary parts, over 15 cwt. It has a bed 6 feet long, and admits a bar 3 feet *This arrangement of collar and guard is neither good nor strong, although frequently adopted in the case of small foot-lathes. The collar should be inside the bored head, behind the nut N. 2 inches between its centres. The bed is 9 inches broad and 6 inches deep. The gap is 9 inches wide and 6 inches deep; consequently the lathe can swing a job of 20 inches diameter clear of the leading screw, and one of 24 inches diameter when this screw is withdrawn from its bearings. The speed-cone has three pulleys, each 2 inches broad, the diameter of the largest being 8 inches and that of the smallest 4 inches. The makers have planed and scraped the bed to a true bearing surface, and have so fixed the gap piece that it cannot wear loose or spring the bed. The movable or loose headstock is gripped to the bed by an eccentric motion worked by a handle, so that it may be instantly clamped in position without the trouble of finding a key to fit the usual nut, and then screwing it gradually home. The upper part of this head, which carries the mandril or spindle, has a side adjustment by means of a side screw, whereby the steel centre may be truly aligned with the corresponding centre of the fast headstock, or it may be moved to the one side or to the other in the case of taper turning. A small oil-holder is cast on the back side of the head to facilitate the oiling of the steel centre without having to look for an oil-can. |