Fig. 1497.
The diameters of the eccentric gear-wheels e and s are equal; hence, c makes a revolution and the cross feed is actuated once for every cutting stroke. The swivel head h is bolted to the end of the slide or ram, as it is sometimes called, a, and is provided with a slide i upon which is a slider j, carrying an apron containing the tool post holding the cutting tool, the construction of this part of the mechanism being more fully shown in [Fig. 1497]. The eccentric gear-wheels r s are so geared that the motion of the slide a during the cutting stroke (which is in the direction of the arrow) is slower than the return stroke, which on account of being accelerated is termed a quick return. Various mechanisms for obtaining a quick return motion are employed, the object being to increase the number of cutting strokes in a given time, without accelerating the cutting speed of the tool, and some of these mechanisms will be given hereafter.
Referring again to the mechanism for carrying the cutting tool and actuating it to regulate the depth of cut in [Fig. 1497], g is the end of the slide a to which the swivel head h is bolted by the bolts a b. The heads of these bolts pass into T-shaped annular grooves in g, so that h may be set to have its slides at any required angle. i is a slider actuated on the slide by means of the vertical feed screw which has journal bearing in the top of h, and passes through a nut provided in i. To i is fastened the apron swivel j, being held by a central bolt not seen in the cut, and also by the bolt at c. In j is a slot, which when c is loosened permits j to be swung at an angle. The apron k is pivoted by a taper pin l, which fits into both j and k. During the cutting stroke the apron k beds down upon j, but during the back stroke the tool may lift the apron k swinging upon the pivot l. This prevents the cutting edge of the tool from rubbing against the work during the return stroke.
Fig. 1498.
Thus in [Fig. 1498] is a piece of work, and it is supposed that a cut is being carried down the vertical face or shoulder at a; by setting the apron swivel at an angle and lifting the tool during the return stroke, its end will move away from the face of the shoulder. The slider i obviously moves in a vertical line upon slides m.