366 Machine Drawing
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d:\N-Design\Des19-1.pm5
The reverse gear is obtained through the gears A-B, G-I and J-H. The gear I is of larger
width mounted at the rear of the gear box and it acts as an idler to reverse the direction of the
output shaft. The position of these gears is shown in Fig. 19.6 (b).
19.2.7 Split-sheave Eccentric
Figure 19.7 shows the assembly drawing of a split-sheave eccentric. In this, sheaves 1 and 2,
forming a circular disc with a stepped rim is housed in two abutting straps 6 and 7. Two shims 8
are used in-between the straps for free movement of the sheave. When the shaft rotates, the
sheave rotates eccentrically, imparting reciprocating motion to the eccentric rod. The eccentric
rod is connected to one of the straps rigidly.
The straps are semi-circular elements, with an annular recess to accommodate the stepped
rim of the sheave. The rotary motion of the sheave is converted into linear motion to the eccentric
rod, through the straps. These are held together on the sheave by means of strap bolts, with
packing strips placed between them. These permit adjustment for wear at a later date. The
eccentric rod is connected to one of the straps by means of studs 11.
19.3 Machine Tool Parts and Accessories
19.3.1 Tool Post
Tool posts of various designs are available to support the cutting tools in lathe machines. Figure
19.8 shows the assembly drawing of a single tool post which supports one cutting tool and is used
on small size lathes. This unit is fixed on the compound rest of the lathe carriage.
The body of the tool post is in the form of a circular pillar 1 with a collar at one end and a
threaded hole at the other end. A vertical slot is also provided to accommodate the tool or tool
holder. The pillar is slid through a square block 5, which finally is located in the T-slot, provided
in the compound rest. The design permits swivelling of the pillar about its vertical axis. A circular
ring 4 is slid over the pillar and wedge 3 is located in the vertical slot of the pillar. The tool or tool
holder is placed over the wedge. By sliding the wedge on the spherical surfaced ring, the tool tip
can be finally adjusted and clamped in position by means of a square headed clamping screw 2,
through the pillar head.
19.3.2 Lathe Slide Rest
This is used for holding and guiding the cutting tool on the lathe machine. It is fixed on the lathe
carriage. The lathe slide rest has a circular base with a cylindrical projection underneath. It is
fixed to the carriage by means of two bolts. The projection enables the slide rest to be fixed at any
angle with respect to the axis of the work.
Figure 19.9 shows the assembly of a lathe slide rest. The upper face of the body 1 has
channel shaped section and machined to act as guides for the slide block 2. The slide block has
a T-slot on the upper side for accommodating the tool holder 3. The bottom of the slide block
is machined to form a guide way on one side and takes a wearing strip 5 for the purpose of
sliding.
