Machine Drawing

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366 Machine Drawing


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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.

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