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After evaluation of designs A, B and C, design C arrived as the most suitable design. So basic positioning of head- stock, tailstock and the tool post are finalized. Now mod- elling for different components inside the headstock, tail stock and tool post assembly is required.
Design for Lathe Subassemblies
Design for Headstock Subassembly
Headstock has been an important part of the lathe machine as it provides primary rotary motion to the work. A servo
Fig. 7 Design for headstock subassembly
motor is used for this purpose. Drill chuck is also used. Bearing is connected to the drill chuck, thus making it rotary.
Servo motor and drill chuck is connected with the help of timing belt. Entire unit is connected with the help of supporting brackets. So the drill chuck will accommodate the workpiece and will rotate along with the servo motor at desired RPM. Thus the primary rotary motion for the workpiece is achieved. The concept can be seen in Fig. 7.
Design for Tailstock Subassembly
The tailstock is used to apply support to the longitudinal rotary axis of a work piece being machined. A tailstock is particularly useful when the work piece is relatively long and slender. Failing to use a tailstock can cause ‘‘chatter’’, where the work piece bends excessively while being cut. Two designs (I and II) are possible for the tailstock. A hole visible in both the designs is meant for accommodating the quill, which will support the rotating workpiece from the other end. In design I (Fig. 8), there is no provision for height adjustment and the entire tailstock will be fixed and in design II (Fig. 9), there are 4 blocks to facilitate the adjustment of height, as it will help in the alignment between the centres. All the blocks will be fastened with the help of two bolts (Fig. 9). Design II appears to be most suitable design and is selected.
Design for Headstock and Tailstock Assembly
The headstock and tailstock assemblies are assembled on the base plate (Fig. 10), thus forming the bed. This bed will be installed on the horizontal Y axis.
J. Inst. Eng. India Ser. C (April–June 2013) 94(2):187–195 191
Fig. 8 Design I, Tailstock without height adjustment
Fig. 9 Design II, Tailstock with height adjustment
Fig. 10 Assembly of headstock and tailstock on the base plate
Fig. 11 Design for tool post subassembly
Design for Tool Post Subassembly
Tool post is responsible to holding the cutting tool, during the machining operation. The tool post design must ensure certain features like, the adjustment of the height of the tool tip for true facing operation, Freedom of rotation of tool such that it can accommodate various tool geometries and facilitate easy switch between orthogonal and oblige mode of machining and Rigid holding of tool.
The plan is to mount the tool post on the vertical Z axis of the machine. The tool will be capable of moving vertically, so easy height adjustment is achieved. The design is inspired from the conventional tool post, shown in Fig. 11.
In this design, the tool holder can be seen with a vertical bolt for holding the tool. The angle section is drilled to
accommodate the tool holder. On placing the tool in the holder and upon complete fastening of the bolt, the tool gets rigidly connected. Further a bottom packing is given to the tool holder to prevent it falling downwards during the tool change. This packing also allows the rotation of the tool holder prior to the fastening of the tool, thus facilitating the orientation of the tool at any desired angle for machining.
Fabrication of Subassemblies