28-09-2013, 01:28 PM
To Perform Spur Gear Cutting Operation
Theory:
(1) Milling is a machining process which is performed with a rotary cutter with
several cutting edges arranged on the periphery of the cutter. It is a multiple
point cutting tool which is used in conjunction with a milling machine. This
process is used to generate flat surfaces or curved profile and many other
intricate shapes with great accuracy and having very good surface finish. Milling
machines are one of the essential machines in any modern machine shop
(2) Based on the directions of movement of the milling cutter and the feeding
direction of the work piece, there are two possible types of milling (a) UP Milling
[Conventional Milling] (b) Down Milling [Climbing Milling]
The Up Milling is the Process of removing metal by a cutter which is rotated
against the direction of travel of the work piece. The thickness of the chip in Up-
milling is minimum at the beginning of the cut and reaches to the maximum when
the cut terminates
The Down milling is the process of removing metal by a cutter which is
rotated in the same direction of travel of the work piece. The thickness of the chip
is maximum when the tooth begins its cut and it reduces to the minimum when the
cut terminates
(3) The Indexing is the operation of dividing the periphery of a piece of work into
any number of equal parts. In Cutting Spur Gear, equal spacing of teeth on the
Gear blank is performed by Indexing
In Simple Indexing, the work piece is positioned by means of the crank,
Index plate and sector arms. The worm attached to the crank must be engaged
with the Worm Wheel on the dividing head spindle. Since there are 40 teeth on the
worm wheel, one complete turn of the Index crank will cause the spindle and the
work piece to rotate one-fortieth of a turn. Similarly, 40 turns of the crank will rotate
the spindle and work piece 1 turn. Thus, there is a ratio of 40:1 between the turns of
the Index crank and the dividing Head spindle. Further Indexing is made possible
by having the Index plates with equi-spaced holes around various circles.