Lathe Related Operations

The lathe, of course, is the basic turning machine. Apart from turning, several other operations can also be performed on a lathe.

1-Straight turning:
Straight turning, sometimes called cylindrical turning, is the process of reducing the work diameter to a specific dimension as the carriage moves the tool along the work. The work is machined on a plane parallel to its axis so that there is no variation in the work diameter throughout the length of the cut. Straight turning usually consists of a roughing cut followed by a finishing cut. When a large amount of material is to be removed, several roughing cuts may need to be taken. The roughing cut should be as heavy as the machine and tool bit can withstand. The finishing cut should be light and made to cut to the specified dimension in just one pass of the tool bit. When using power feed to machine to a specific length, always disengage the feed approximately 1/16-inch away from the desired length dimension, and then finish the cut using hand feed.

2-Boring:
Boring always involves the enlarging of an existing hole, which may have been made by a drill or may be the result of a core in a casting. An equally important, and concurrent, purpose of boring may be to make the hole concentric with the axis of rotation of the workpiece and thus correct any eccentricity that may have resulted from the drill's having drifted off the center line. Concentricity is an important attribute of bored holes. When boring is done in a lathe, the work usually is held in a chuck or on a face plate. Holes may be bored straight, tapered, or to irregular contours. Boring is essentially internal turning while feeding the tool parallel to the rotation axis of the workpiece.

3-Facing:
Facing is the producing of a flat surface as the result of a tool's being fed across the end of the rotating workpiece. Unless the work is held on a mandrel, if both ends of the work are to be faced, it must be turned end for end after the first end is completed and the facing operation repeated. The cutting speed should be determined from the largest diameter of the surface to be faced. Facing may be done either from the outside inward or from the center outward. In either case, the point of the tool must be set exactly at the height of the center of rotation. because the cutting force tends to push the tool away from the work, it is usually desirable to clamp the carriage to the lathe bed during each facing cut to prevent it from moving slightly and thus producing a surface that is not flat. In the facing of casting or other materials that have a hard surface, the depth of the first cut should be sufficient to penetrate the hard material to avoid excessive tool wear.

4-Parting:
Parting is the operation by which one section of a workpiece is severed from the remainder by means of a cutoff tool. Because cutting tools are quite thin and must have considerable overhang, this process is less accurate and more difficult. The tool should be set exactly at the height of the axis of rotation, be kept sharp, have proper clearance angles, and be fed into the workpiece at a proper and uniform feed rate.

5-Threading:
Lathe provided the first method for cutting threads by machines. Although most threads are now produced by other methods, lathes still provide the most versatile and fundamentally simple method. Consequently, they often are used for cutting threads on special workpieces where the configuration or nonstandard size does not permit them to be made by less costly methods. There are two basic requirements for thread cutting. An accurately shaped and properly mounted tool is needed because thread cutting is a form-cutting operation. The resulting thread profile is determined by the shape of the tool and its position relative to the workpiece. The second by requirement is that the tool must move longitudinally in a specific relationship to the rotation of the workpiece, because this determines the lead of the thread. This requirement is met through the use of the lead screw and the split unit, which provide positive motion of the carriage relative to the rotation of the spindle.

6-Knurling:
Knurling is a manufacturing process, typically conducted on a lathe, whereby a visually-attractive diamond-shaped (criss-cross) pattern is cut or rolled into metal. This pattern allows human hands or fingers to get a better grip on the knurled object than would be provided by the originally-smooth metal surface. Occasionally, the knurled pattern is a series of straight ridges or a helix of "straight" ridges rather than the more-usual criss-cross pattern.

7-drilling:
Frequently, holes will need to be drilled using the lathe before other internal operations can be completed, such as boring, reaming, and tapping. Although the lathe is not a drilling machine, time and effort are saved by using the lathe for drilling operations instead of changing the work to another machine. Before drilling the end of a workpiece on the lathe, the end to be drilled must be spotted (center-punched) and then center-drilled so that the drill will start properly and be correctly aligned. The headstock and tailstock spindles should be aligned for all drilling, reaming, and spindles should be aligned for drilling, reaming, and tapping operations in order to produce a true hole and avoid damage to the work and the lathe. The purpose for which the hole is to be drilled will determine the proper size drill to use. That is, the drill size must allow sufficient material for tapping, reaming, and boring if such operations are to follow.
The correct drilling speed usually seems too fast due to the fact that the chuck, being so much larger than the drill, influences the operator's judgment. It is therefore advisable to refer to a suitable table to obtain the recommended drilling speeds for various materials


8-spinning operation:
Metal Spinning is a process by which circles of metal are shaped over mandrels (also called forms) while mounted on a spinning lathe by the application of levered force with various tools. It is performed rotating at high speeds on a manual spinning lathe or performed by CNC controlled automated spinning machines. The flat metal disc is clamped against the mandrel and a series of sweeping motions then evenly transforms the disc around the mandrel into the desired shape.

Metal spinning ranges from an artisan's specialty to the most advantageous way to form round metal parts for commercial applications. Artisans use the process to produce architectural detail, specialty lighting, decorative household goods and urns. Commercial applications range from rocket nose cones to public waste receptacles. Other methods of forming round metal parts include hydro forming, stamping and forging or casting. Hydro forming and stamping generally have a higher fixed cost, but a lower variable cost than metal spinning. Forging or casting have a comparable fixed cost, but generally a higher variable cost. As machinery for commercial applications has improved, parts are being spun with thicker materials in excess of 1" thick steel.
The basic hand metal spinning tool is called a spoon, though many other tools (be they commercially produced, ad hoc, or improvised) can be used to effect varied results. Spinning tools can be made of hardened steel for using with aluminum or solid brass for spinning stainless steel/mild steel. Commercially, rollers mounted on the end of levers are generally used to form the material down to the mandrel in both hand spinning and CNC metal spinning. Rollers vary in diameter and thickness depending the intended use. The wider the roller the smoother the surface of the spinning, the thinner rollers can be used to form smaller radii.
The mandrel/chuck can be made from wood, steel alloys, or synthetic materials. The choice of material is dictated by the hardness of the material to be spun and by how many times the tool is expected to be used.
Metal spinning can be accomplished using a wide variety of materials from soft tempered aluminum and copper to structural plate steel and stainless steels.
The manual lathe in question is sometimes a regular woodworking lathe, although a Wilson lathe is the most common manual spinning lathe in the UK. The mandrel having been formed from wood on the lathe or steel chuck machined on a CNC lathe previous to mounting on the metal stock. Cutting of the metal is done by hand held cutters, often foot long hollow bars with tool steel shaped/sharpened files attached. This is dangerous and should only be done by skilled tradesmen. All stock sizing is done prior to the spinning.

9-Reaming On Tthe Lathe:
Reamers are used to finish drilled holes or bores quickly and accurately to a specified diameter. When a hole is to be reamed, it must first be drilled or bored to within 0.004 to 0.012 inch of the finished size since the reamer is not designed to remove much material.
The hole to be reamed with a machine reamer must be drilled or bored to within 0.012 inch of the finished size so that the machine reamer will only have to remove the cutter bit marks.
The workpiece is mounted in a chuck at the headstock spindle and the reamer is supported by the tailstock in one of the methods described for holding a twist drill in the tailstock.
The lathe speed for machine reaming should be approximately one-half that used for drilling.
The hole to be reamed by hand must be within 0.005 inch of the required finished size.
The workpiece is mounted to the headstock spindle in a chuck and the headstock spindle is locked after the piece is accurately setup The hand reamer is mounted in an adjustable tap and reamer wrench and supported with the tailstock center. As the wrench is revolved by hand, the hand reamer is fed into the hole simultaneously by turning the tailstock handwheel.
The reamer should be withdrawn from the hole carefully, turning it in the same direction as when reaming. Never turn a reamer backward.