Lathe Machine Assignment: External Lathe Operation

Facing Operation

a process of removing metal from the end of a work piece to produce a flat surface

Work piece is cylindrical but using a 4 jaw chuck able to face rectangular or odd-shaped work to form cubes and other non-cylindrical shapes.

Preparing the Facing Cut

The tumbler gear lever should be in the neutral position to prevent the leadscrew does not rotate. During the facing operation, the leadscrew should be clamp half to prevent the saddle from being forced back from the end of the workpiece by the force of the cutting operation.

To run the operation properly, the work should be properly centered by the jaws touch the surface of the work. The workpiece is then twist in the jaws to seat it.

Beginning the Facing Cut

Use the compound crank to advance the tip of the tool until it just touches the end of the workpiece.Use the cross feed crank to back off the tool until it is beyond the diameter of the workpiece.
Turn the lathe on and adjust the speed to a few hundred RPM - about 10 O'clock setting of the speed control knob. Now slowly advance the cross feed crank to move the tool towards the workpiece.
When the tool touches the workpiece it should start to remove metal from the end.

The Roughing Cut

Use the compound crank to advance the tool towards the chuck about .010" (ten one-thousandths of an inch, or one one-hundredth of an inch).

If the compound is set at a 90 degrees to the cross slide (which is how I usually set mine) then each division you turn the crank will advance the tool .001 (one one-thousandth of an inch) toward the chuck.

If the compound is set at some other angle, say 30 degrees, to the cross slide, then it will advance the tool less than .001 for each division. The exact amount is determined by the trigonometric sine of the angle. Since the sine of 30 degrees is .5 the tool would advance .0005 (five ten-thousandths or 1/2 of one one-thousandth of an inch) for each division in this example.

Cutting on the Return Pass

crank the tool back towards you after it reaches the center of the workpiece you will notice that it removes a small amount of metal on the return pass. This is because the surface is not perfectly smooth and it is removing metal from the high spots.

If you need to remove a lot of metal, to reduce the workpiece to a specific length, for example, you can take advantage of this return cut to remove more metal on each pass by advancing the tool a small ways into the workpiece on the return pass. Since the tool must plunge into the face of the workpiece, this works best with a fairly sharp pointed tool.

The Finishing Cut

Depending on how rough the end of the workpiece was to begin with and how large the diameter is, you may need to make 3 or more passes to get a nice smooth finish across the face. These initial passes are called roughing passes and remove a relatively large amount of metal.

a final finishing cut to remove just .001 to .003" of metal and get a nice smooth surface.

The finishing cut can also be made at higher RPM (say 1500 RPM) to get a smoother finish.

Straight Turning Operation

Turning is the process whereby a centre lathe is used to produce "solids of revolution". I

When turning, a piece of material (wood, metal, plastic even stone) is rotated and a cutting tool is traversed along 2 axes of motion to produce precise diameters and depths.

Turning can be either on the outside of the cylinder or on the inside (also known as boring) to produce tubular components to various geometries. Although now quite rare, early lathes could even be used to produce complex geometric figures, even the platonic solids; although until the advent of C.N.C it had become unusual to use one for this purpose for the last three quarters of the twentieth century.

2. Facing is part of the turning process.

It involves moving the cutting tool across the face (or end) of the workpiece and is performed by the operation of the cross-slide, if one is fitted, as distinct from the longitudinal feed (turning). It is frequently the first operation performed in the production of the workpiece, and often the last- hence the phrase "ending up".

The bits of waste metal from turning operations are known as chips (North America), or swarf in Britain. In some locales they may be known as turnings.

The turning processes are typically carried out on a lathe, considered to be the oldest machine tools, and can be of four different types such as straight turning, taper turning, profiling or external grooving. Those types of turning processes can produce various shapes of materials such as straight, conical, curved, or grooved workpiece. In general, turning uses simple single-point cutting tools. Each group of workpiece materials has an optimum set of tools angles which have been developed through the years.

Aluminium, copper alloys, steels, stainless steels, high-temperature alloys, refractory alloys, titanium alloys, cast irons, thermoplastics, thermosets, etc… are examples of different type of materials used

Material removal rate

The material removal rate (MRR) in turning is the volume of material removed per unit time in mm³/min. For each revolutionof the workpiece, a ring-shaped layer of material is removed.

MRR = pi×D_avg×d×f×N where

D_avg: Average diameter
N: Rotational speed of the workpiece
f: Feed
d: Depth of cut

The forces acting on a cutting in turning are important in the design of machine tools. The machine tool and its components must be able to withstand these forces without causing significant deflections, vibrations, or chatter during the operation. There are three principal forces during a turning process: cutting force, thrust force and radial force.

The cutting force acts downward on the tool tip allowing deflection of the workpiece upward. It supplies the energy required for the cutting operation.
The thrust force acts in the longitudinal direction. It is also called the feed force because it is in the feed direction of the tool. This force tends to push the tool away from the chuck.
The radial force acts in the radial direction and tends to push the tool away from the workpiece.

Although it requires less-skilled labor, the engine lathes do need skilled labor and the production is somewhat slow. Moreover, it can be accelerated by using a turret lathe (In a turret lathe, a longitudinally feedable, hexagon turret replaces the tailstock. The turret, on which six tools can be mounted, can be rotated about a vertical axis to bring each tool into operating position, and the entire unit can be moved longitudinally, either mannually or by power, to provide feed for the tools) and automated machines.