The above diagram shows the mechanism as used on the apparatus.
Link 1 on the top diagram is extended to point A. Attached to point A is
another link with a pivot. The other end of this link terminates in a slider.
In a machine tool where this mechanism is used the cutting tool is attached to
this slider.
The link POA rotates about O. The mechanism is driven by crank PC
which rotates about C with constant velocity. The slider at P slides along POA
as the crank is turned. Its path is shown by the dashed circle, centered on C
and through P. Clearly when P is at P1 the slider S is at the outer extremity
of its travel. When P is at P2 the slider S is at the inner extremity of its
travel.
Now as PC rotates with constant velocity the time taken to go from
P1 to P2 is less than that taken to go from P2 to P1. However during both those
time intervals the slider S is moving the same distance. Therefore the speed of
S is different during the different parts of the cycle. During the shorter time
interval P1 to P2 the slider S has the greater speed and during the interval P2
to P1 it has the slower speed. Thus P1 to P2 is the quick return and P2 to P1
the slower cutting stroke.
When applied to a metal cutting machine (a shaping machine) the
other advantage of the mechanism is the variable power distribution during the cycle.
When S is on the return stroke the slider at P is nearer to O and simple
moments shows that the torque applied is low. Hence the return stroke uses less
power as P = T.ω. During the cutting stroke the slider at P is at a greater
radius from O and thus more power is available to perform useful work in
cutting metal.
Thus the overall performance of the mechanism is to provide a high
power forward cutting stroke with a low power and higher speed quick return in
preparation for the next cut.
REFERRED BY :- ER. VIKRAM KHARB (A.P.), MECHANICAL ENGG. DEPTT., SGI
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