Basic Manufacturing Process - Ch.7.2

Q.4    Describe various operations performed on a lathe machine.                         (AKTU - 2008-09)
Related Questions -
Q.    List the operations performed on lathe machine.                                            (AKTU - 2011 - 12)
Ans.    Various Operations Performed on a Lathe Machine: -
1. Turning: -

    It is the operation of reducing the diameter of a workpiece. A simple single point cutting tool is used for turning operations. Turning can be of different types-like taper turning, straight turning, profiling,external grooving, etc. The depth of cut is given by movement of cross-slide.
2. Facing: -
    Facing is the operation of reducing the length of a workpiece. A lathe machine can be used to create a smooth and flat face perpendicular to the axis of cylindrical part.
3. Taper Turning: -
                           
D - major diameter of work, d -  minor diameter of work, l -  length of workpiece, a - taper angle
       
A taper is defined as a uniform change in diameter of a workpiece measured along the length of it. It can also be expressed as a ratio of difference in diameter to the length of a work. It is also expressed in degree of help the included angle.
    Short taper turning can be done by swivelling compound slide and working the tool manually. Long taper can be produced by offsetting the tail stock body with respect its base.
4. Drilling: -
    Drilling is the operation of producing a fresh hole in a workpiece. The drill bit is held in the tail stock and workpiece is held in the head stock.
 5. Boring: -
    Boring is the operation of enlarging the diameter of a hole in a workpiece. The workpiece is held in a chuck or on a face plate during this operation. Holes may be bored straight, tapered.
6. Parting: -
    When all the machining processes have been completed, the finished job is cut off from the parent bar stock. This operations is used for cutting a desired length from the bar stock.
7. Threading: -
    Threading is a form cutting operations which is done by a special cutting tool called threading tool. Threads can be produced either on internal or external surface of a cylindrical bar.
8. Knurling: -
    It is a process of impressing a diamond shape or straight line pattern in the surface of a workpiece by special shaped hardened metal wheels to improve its appearance and to give a better grip to the workpiece.
9. Polishing: -
    Polishing is basically a surface finishing operation with abrasive particles embedded on cloth or a paper. Emery abrasive cloth is best suited for ferrous metals while abrasive paper can be used for non ferrous metals.
10. Filing: -
    Mill files are considered best for lathe filing operation. The bastard cut mill type hand file is employed for roughing and second cut mill type hand file is employed for fine class of work.

Q.5    With the help of schematic sketch, describe the basic working principle and important parts of shaper machine. Also describe the difference in operation between shaper and planer.                                                                                                                                        (AKTU - 2008-09, 09-10)
Related Questions -
Q.    What are the main differences between a shaper and planer? Which are the drive mechanisms used in shaper? Discuss any one in brief with neat sketch.          (AKTU - 2011 - 12)
Q.    Briefly describe planer machine.
Ans.    Shaper: -

    Shapers have been largely superseded by milling machines or grinding machines in modern industrial practice. They rapidly fell out of favour with modern industry as they were time consuming in operation, the amount of material removal by a single point cutting tool being no match for recent methods, however they are still popular with some amateurs, or where production time is not a factor. The basic function of the machine is still sound and tooling for them is minimal and very cheap to reproduce. The mechanically operated machines are simple and robust in construction, making their repair and upkeep easily achievable.
    The shaper is a relatively simple machine and is used fairly often in the toolroom or for machining one or two pieces for prototype work. Tooling is simple, and shapers do not always require operator attention while cutting.
Working Principle: -
    The shaper is used to machine flat surfaces, which may be horizontal, vertical or angular planes. While primarily used to machine flat surfaces, a skillful machinist can manipulate a shaper to cut curved and irregular shapes, slots, grooves and keyways. Because of the way the machine operates, the cutting tool travels back and forth over the work. The shaper usually cut only in one direction, so that the return stroke is lost time. However, the return stroke is made at up to twice the speed of the cutting stroke.
Principle Parts of Shaper: -
    The horizontal shaper is the most common type, and its principal components are shown in figure and described as follows -
Ram: -
    The ram slides back and forth in dovetail or square ways to transmit power to the cutter. The starting point and the length of the stroke can be adjusted.
Tool head: -
    The tool head is fastened to the ram on a circular plate so that it can be rotated for making angular cuts. The tool head can also be moved up or down by its hand crank for precise depth adjustments. Attached to the tool head is the tool holding section. This has a tool post very similar to that used on the engine lathe. The block holding the tool post can be rotated a few degrees so that the cutter may be properly positioned in the cut.
Clapper Box: -
    The clapper box is needed because the cutter drags over the work on the return stroke. The clapper box is hinged so that the cutting tool will not dig in. Often this clapper box is automatically raised by mechanical, air, or hydraulic action.
Table: -
    The table is moved left and right, usually by hand, to position the work under the cutter when setting up. Then, either by hand or more often automatically, the table is moved sideways to feed the work under the cutter at the end or beginning of each stroke.
Saddle: -
    The saddle moves up and down (Y axis), usually manually, to set the rough position of the depth of cut. Final depth can be set by the hand crank on the tool head.
Column: -
    The column supports the ram and the rails for the saddle. The mechanism for moving the ram and table is housed inside the column.
Tool holders: -
    Tool holders are the same as the ones used on an engine lathe, though often larger in size. The cutter is sharpened with rake and clearance angles similar to lathe tools, though the angles are smaller because the work surface is usually flat. These cutters are fastened into the tool holder, just as in the lathe, but in a vertical plane.
Work Holding: -
    Work holding is frequently done in a vise. The vise is specially designed for use in shapers and has long ways, which allow the jaws to open up to 14 inches or more; therefore quite large work pieces can be held. The vise may also have a swivel base so that cuts may be made at an angle. Work, which, due to size or shape, cannot be held in the vise, is clamped directly to the shaper table in much the same way as parts are secured on milling machine tables.
Operations Performed on Shaper: -
Shaper can Used –
(1)     For making a rectangular job   
 (2) For making a ‘v’ shape job
(3)     For making square head of nut or bolt   
(4)     For making hexagonal head of nut or bolt
(5)     For cutting keyway.
Planer: -
    A planer makes the same types of cuts as a shaper. However, it is a production-type machine for certain types of work. It can machine any flat or angular surface, including grooves and slots, in medium and large sized workpieces. The workpiece is clamped onto the worktable and the worktable is reciprocated while the tool is held stationary. The tool is only moved to provide a feed when the workpiece is moving on the return stroke. The worktable moves on hardened ways and is designed for large size work. As the tool post and the bedplate are designed to be very rigid the planer can take very heavy cuts and can machine very accurately. Typical work would be machine beds and columns, marine diesel engine blocks, and bending plates for sheet metal work. These parts are usually large iron castings or steel weldments and may weigh a few hundred pounds or several tons.
Principal Parts of Planer: -
    The most frequently used type of planer is the double-housing planer, shown in Fig. with the following components:
Frame: -
    The frame is basically two heavy columns fastened together at the top with a large bracing section and fastened at the bottom to the machine bed. This creates a very strong, rigid structure, which will handle heavy loads without deflection.
Crossrail: -
    The crossrail is also a heavy box, or similar construction. It slides up and down on V- or flat ways, controlled by hand or by power- operated screws. These crossrails are so heavy that they are counterweighted, with either cast iron weights or hydraulic cylinders, in order that they may be moved easily and positioned accurately. After being positioned they are clamped in place.
Railheads: -
     The two railheads can be moved left or right across the crossrail, each controlled by a separate lead screw, which can be turned by hand but usually by power feed. The railhead can be rotated, and vertically adjusted for depth of cut, the same as the shaper heads. They also have a clapper box (often with power lift) like the shaper.



Sideheads: -
    The sideheads are independently moved up or down by hand or by power feed and can also be rotated and moved in or out for depth of cut.
Table: - 
    The table is a heavy casting, which carries the work past the cutting heads. It runs on V- or flat ways. The table is driven either by a very long hydraulic cylinder or by a pinion gear driving a rack, which is fastened under the centre of the table. The motor driving the pinion gear is the reversible type with variable speed.
Bed: -
    The bed of the planer must be a weldment of casting twice as long as the table. Thus a 12-ft table requires a 24-ft bed. The gearing of hydraulic cylinders for driving the table is housed under the bed.
Tool holdes: -
    Planers use high speed steel or carbide tipped cutting tools similar to those used on shapers. However, since planers make heavy cuts, their tools are much larger.
Work Holding: -
    Holding the work while machining such heavy cuts at 60 to 100 feet per minute requires considerable force; therefore, the workpieces must be solidly fastened to the table. Because the reversal of direction occurs quite rapidly, the work must be especially well braced at the ends. The table has T-slots, both lengthwise and across, in which heavy bolts and clamps may be used. Sometimes holes are drilled in the table so that large pins can be used to prevent the workpiece from going off the table when the machine reverses.
Planer: -
    Planner are also fall under the group of reciprocating machine tools. It is very large and massive compared to a shaper and is capable of machining heavy workpiece. The fundamental differences between shaper and planner are given below.



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