Wilson, Joseph M. (ed.) / The Masterpieces of the Centennial International Exhibition illustrated: history, mechanics, science
Wilson, Joseph M.
Mechanics and science, pp. -375 ff.
THE INTERNATIONAL EXHIBITION, i876. pulley-shaft. At each change of motion the pawl is thrown into gear by friction, keeping up a positive motion of the crank-disk by the ratchet-wheel until the pawl is disengaged from its teeth by a positive stop. Messrs. Sellers' method of lifting the tool-point on back motion in this machine merits attention as another improvement on the usual plan, which, in most planing-machines consists in hanging the cutting-tool in what is called an apron, so adjusted as to allow it to swing loose on the back stroke, but to be held rigidly when cutting. This arrangement is very objectionable in all fine planing, and especially in large planers where the tool is quite heavy. Various ideas have been put into practice for actually lifting the tool-point clear of the work on the back stroke and dropping it into place again ready for action on the return, but the method here shown possesses especial ingenuity, lifting the tool in every position of the slide-rest, and doing so from within the cross-head without interfering in any way with the automatic feed motion, the machinery for working the feeds occupying the centre about which the adjustable part of the saddle rotates. This lifting apparatus is operated by a cord attached to a grooved segment which is connected with the crank-plate of the feed motion by a link, a reciprocating motion being imparted to the cord corresponding with the motions of the table, and occurring only at the end of each table movement, beginning with the reversion of each stroke. The cord is guided over sheaves at the ends of the cross-head and passes around a cord-wheel in the saddle, having at its other end a weight to keep it in tension. The' cord-wheel, by means of a pinion at the other end of its shaft, operates on a light annular plate-wheel recessed into the saddle, around the central part containing the small feed bevels. In a spiral groove on the face of this plate-wheel slides a block which is attached to the end of a pipe surrounding the vertical feed-screw, and extending upward through the casting, with a pair of elastic clamps at its upper end. These clamps operate by friction on a flat rod which passes the whole length of the vertical slide on its side next to the saddle, and has at its lower end, which is thickened up, a hole. The long arm of a bell-crank lever fits loosely into this hole, and the short arm extends down directly behind the tool-apron. The action of the cord imparts motion to this bell-crank and affects the tool apron, pushing it forward and letting it fall back again into place as required. The action is perfect and beautiful, with- out interference with any of the functions of the machine in the least. When the 22
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