Fig. 1550.
The principle of action when a vibrating link is employed may be understood from [Fig. 1550], in which p is a pinion driven by the cone pulley and imparting motion to d. At l is a link pivoted at c. At a is a link block or die capable of sliding in the slot or opening in the link and a working fit upon a pin which is fast in the wheel d. As d rotates the link block slides in the slot and the link is caused to travel as denoted by the dotted lines. r is a rod connecting the tool-carrying slide s to the upper end of link l, and therefore causing it to reciprocate with l. But s being guided by its slide in the guideway traverses in a straight line.
Since the rotation of p and d is uniform, the vibrations of the link l will vary in velocity, because while the link block is working in the lower half of the link slot it will be nearer to the centre of motion c of the link, and the upper end of c will move proportionately faster. The arrangement is such that during this time the tool-carrying slide is moved on its return stroke, the cutting stroke being made while the link block is traversing the upper half of the slot, or in other words, during the period in which the crank pin in a is above the horizontal centre of wheel d.
Now suppose the arrangement of the parts is such that the front of the machine or the cutting tool end of the slide is at the end k of s, then s will be pushed to its cut by the rod r at an angle which will tend to lift s in the slideways. But suppose the direction of rotation of wheel d instead of being as denoted by the arrow at d be as denoted by the arrow at e, then s will be on its back stroke, the front of the machine being at j. In this case rod r will pull s to the cut, and s will, from the angularity of r, be pulled down upon the bed of the slideway guiding it, and will therefore be more rigidly held and less subject to spring, because the tendency to lift is resisted on one side by the adjustable gib only, and on the other by the projecting v, whereas the tendency to be pulled downwards is resisted by the strength of the frame of the machine.
Furthermore, as the pressure on the cutting tool is below the level of the tool-carrying slide it tends to force that slide down upon the slideway, and it will therefore be more rigidly and steadily guided when the force moving the slide and the tool pressure both act in the same direction.
To vary the length of stroke of s pin a is so attached to wheel d that it may be adjusted in its distance from the centre of d.
