The square, or straight-line Muck, is peculiar to the rose-engine, and forms a very material part of it ; the object of it is to lay the patterns in a straight instead of a circular direction. Fig. 25 represents the straight-line chuck ; the square frame, A A, is fastened to the two ante of the headstock, shown in fig. 21, by bolts and nuts, or wedges; B, B, ie a slide connected with the nose of the mandril either by a chain or, what is better, a rack and pinion. On the face of the elide are click and scrow-plates, and a nose to receive the chucks, as in the excentric and oval chucks. a, fig. 26, is the wave of which the patterns B, 0, D, E, and r are composed, by notches in the plate. These speci mens will serve to show the immense number of patterns which may be produced with twenty or thirty rosettes and their combinations. Many curious patterns are produced by using two rosettes, one fixed to the mandril, the other on the cannon. For cutting copper and steel plates, or wood blocks, the tool is sharpened with two acute angles ; but in turning gold and silver work the quantity of metal taken off is required to be so minute that the two faces of the tool must be rubbed to such an obtuse angle as to appear almost straight. Close to the aide of the tool in the rest is placed a stop, or touche, as it is called, to regulate the depth of the cut. The teuche has a very small face,
highly polished, which rubs upon the work in advance of the tool The number of adaptations, on account of the various and irregular shapes of the different pieces of work to be engine-turned, is very large, and would take up far too much space to describe. Cutting the rosettes, which every engine-turner ought to do for himself, is an ope ration of considerable nicety, as the waves are mostly very shallow, and the rosettes Large. to make them work easily, and the slightest fault in a wave will be repeated through the whole work. Two superior ma chines for engine-turning were invented by Messrs. Perkins and Heath, some years ago, in which the rosettes are dispensed with, and their place supplied by an excentric wheel, or cam, which produces one wave only ; but by means of toothed wheels, as many of these waves as are requisite aro introduced during each revolution of the mandril. This engine produces an immense variety of patterns, with the very great advantage of all the waves being precise counterparts of each other. Work of this description is generally cut with a diamond, as a steel tool is liable to break, or get dull, and destroy tho uniformity of the effect.