Setting of Job on Slotter
Work is not mounted directly on
the table but on the parallel strips laid on the table in order to give
clearance for the tool. Here the height of the parallel strips should be such as
to give work clearance so that the tool will move past the lower edge of the
work and have enough table clearance so that the tool will not strike the table
when the ram is at the end of the cutting stroke. If the tool strikes the
table, it will break and may result in other damage to the machine.
Cutting of internal Keyways in Bush
The following procedure is to be
adopted for cutting keyways in bush.
(a) Scribe the centreline across
the boss and mark the width of the key way. Set the job on the pair of parallel
strips of about 1/2” height and clamp it.
(b) Obtain a keyway cutting tool
and clamp it in the tool holder. Adjust the stroke of the ram to suit the ram
so that the tool just clears the table at bottom of the stroke.
(c) Set the tool central to the
marking out and commence to slot the keyway, feeding very gradually by hand.
When nearing the depth, measure it with vernier callipers.
(d) Finally finish the full depth
of keyway.
Cutting of External Keyways
With suitable tools, a slotter
can very conveniently machine slots or grooves on a work or cut external
keyways on shaft. For cutting keyways, a square nose tool similar to a parting
off tool is selected. External keyways are cut on a shaft by first drilling a
hole at the blind end of the keyway. The diameter of the hole should be 0.5 to
0.8 mm oversize than the width of the keyway and the depth should be about 1.5
mm deeper than the depth of the keyway. This is necessary to leave a clearance
on the tool at the end of the stroke. The length and position of stroke is
carefully adjusted so that the stroke will terminate exactly at the clearance
hole. The speed is reduced while cutting keyways.
The following procedure is to be adopted
for cutting Serrations.
(a) The slotting machine with
circular table provides a convenient means of cutting internal or true external
Serrations.
(b) Set the work on two parallel
strips on the Circular table.
(c) True the outside diameter
using a dial test indicator held in the tool box.
(d) Put two or three clamps round
the outside and secure it tightly.
(e) A V-tool would be used for
cutting serrations and it would be fed to the same depth in each indexing.
(f) The indexing of the circular
table would have to be carried out to suit the number of slots being cut, the
angle being found by dividing 3600 by the number of serrations to be cut on the
periphery of the work.
(g) Index to each position and
finish slotting of serrations to the same depth.
Quick Return Motion (QRM)
Quick return motion is employed
in slotting machine during upward return
stroke to reduce the time of non-cutting stroke time, thereby reducing the
production time. This is obtained by two methods. These are mentioned below:
(a) QRM is obtained by using a slotted
crank lever mechanism.
(b) QRM by using Whitworth Quick
Return Mechanism.
The ram is actuated by connecting
rod and adjustable crank driven by gearing or suitable pulleys. The pinion
drives the bull gear. Across the face of the bull gear there is dovetail slide
which carries the crank block on which sliding block is fitted. The sliding
block slides in the slot of the link lever. A driving rod connected to a pin is
fixed at the rear of the ram. The stroke of the ram is altered by the radial
adjustment of the driving gear attached to the crank block.
Feed Mechanism. In a slotter, the
feed is given by the table. A slotting machine may have three types of feed
movements. The feed movements may be supplied by either by hand or power.
(a) Longitudinal
(b) Cross
(c) Circular
Hand Feeding Mechanism
The hand feeding mechanism for
the reverse, longitudinal and circular movement of the table consists of three
screw rods operated by crank handle, which may be attached to the square end of
the feed rods.
Power Feeding Mechanism
The power feed mechanism makes
use of a ratchet and pawl mechanism. A cam groove 1 is cut on the face of the
bull gear in which a roller 2 slides. As the bull gear rotates, the roller
attached to a lever 3 follows the contour of the cam groove and moves up and
down only during a very small part of revolution of the bull gear. The cam
groove may be so cut that the movement of the lever 3 will take place only at
the beginning of cutting stroke. The rocking movement of the lever 3 is
transmitted to the ratchet and pawl mechanism 6 and 8, so that the ratchet 8
will move in one direction only during this short period of time. The ratchet
wheel is mounted on a feed shaft which may be engaged with cross, longitudinal
or rotary feed screws individually or together to impart power feed movement to
the table.
The length of stroke of ram can
be varied by altering the position of pin with respect to the centre of the
disc. Farther the position of the pin with respect to the disc centre, greater
will be the throw of eccentricity and longer will be the stroke length. The
stroke is to be set in the following sequence.
(a) Bring the ram to its bottom
most position.
(b) Set the length of stroke half
inch more than the length of job by rotating the driving gear with hand and
reading directly by the stroke indicator on the scale.
(c) Unclamp the ram which is
still in the bottom most position and adjust the position of tool so that the
cutting point of the tool goes ¼” below the machine surface or clear in the
slot or recess provided for tool clearance by bringing the ram down.
(d) Clamp the ram and check the
setting by moving the Ram up and down by hand wheel.
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