Learn Machining Processes Explained – Turning, Milling, Drilling, Boring, Shaping, Planing, Broaching, Sawing – Their Operations, Machines and Design Considerations

Introduction:

Machining processes form the essential foundation of modern manufacturing, enabling the production of components that range dramatically in size and complexity. The typical products made through machining include miniature screws for the hinges of eyeglass frames, which require extreme precision and fine detail, as well as massive components such as turbine shafts for hydroelectric power plants, rolls for rolling mills and gun barrels. The starting material for machining operations is generally a workpiece that has been produced by other manufacturing processes, including casting, forging, extrusion, drawing or powder metallurgy. Each of these preceding processes imparts specific characteristics to the workpiece that influence the subsequent machining operations, such as initial shape, material properties and surface condition.

Machining fundamentally involves the controlled removal of material from a workpiece to achieve desired dimensions, geometric features and surface finishes. The selection of appropriate machining processes depends on numerous factors including the material being machined, the required accuracy and surface finish, production volume and economic considerations. This comprehensive guide explores the major machining operations, their capabilities, the machines that perform them and their applications across various industries. Understanding these processes is crucial for manufacturing engineers, designers and production professionals who must select optimal methods for specific applications while balancing quality, productivity and cost.

Turning Operations and Lathe Applications:

Turning represents one of the most basic and versatile machining processes. In turning, the part is rotated while it is being machined, with the cutting tool removing material to create cylindrical, conical or contoured surfaces. These operations typically are carried out on a lathe or by similar machine tools which are highly versatile and capable of a number of machining processes that produce a wide variety of shapes.

Fundamental Turning Operations:

Straight turning produces cylindrical workpieces with uniform diameter along their length, such as shafts, spindles and pins. The cutting tool moves parallel to the axis of rotation, removing material to achieve the desired outside diameter. Taper turning creates conical shapes by feeding the tool at an angle relative to the axis of rotation rather than parallel to it. This produces tapered cylinders or conical shapes that are essential for applications requiring gradual diameter changes such as in machine tool spindles and automotive components.

Contour turning involves feeding the tool along a path that is not straight, instead following a contour that creates curved or irregular profiles in the turned part. This operation allows for complex geometries that serve functional purposes such as aerodynamic shapes, or aesthetic purposes, such as decorative features on consumer products. Form turning, sometimes called forming uses a specially designed tool that has a shape imparted to the workpiece by plunging the tool radially into the rotating material. This operation can produce various axisymmetric shapes efficiently, reducing the number of operations required.

Facing produces a flat surface at the end of the part and perpendicular to its axis. This operation is particularly useful for parts that are assembled with other components, as it creates a clean, flat reference surface for mating with other parts. Face grooving produces grooves for applications such as O ring seats which are critical for sealing in fluid power systems and other assemblies. Chamfering uses the cutting edge of the tool to cut an angle on the corner of the cylinder forming a chamfer that facilitates assembly and reduces stress concentrations at sharp corners.

Parting also called cutting off, is an operation where the tool is fed radially into the rotating workpiece at some location along its length to cut off the end of the part. This operation is essential in producing slugs or blanks for additional processing into discrete products and it is frequently used in high production environments. Threading produces external or internal threads using a pointed tool that is fed linearly across the outside surface of the rotating work part in a direction parallel to the axis of rotation at a large effective feed rate thus creating threads in the cylinder.

Knurling produces a regularly shaped roughness on cylindrical surfaces, as in making knobs and handles where a textured surface is desired for grip. Notably, knurling is not a machining operation because it does not involve cutting of material. Instead, it is a metal forming operation used to produce a regular cross hatched pattern in the work surface. The knurling tool consists of two hardened forming rolls each mounted between centers with the desired knurling pattern on their surfaces. To perform knurling, the tool is pressed against the rotating work part with sufficient pressure to impress the pattern onto the work surface.

Tooling for Turning Operations:

Most lathe operations use single point tools. Turning, facing, taper turning, contour turning, chamfering and boring are all performed with single point tools. A threading operation is accomplished using a single point tool designed with a geometry that shapes the thread, requiring careful tool design to produce accurate thread profiles. Certain operations require tools other than single point designs. Form turning is performed with a specially designed tool called a form tool where the profile shape ground into the tool establishes the shape of the work part. A cutoff tool is basically a form tool designed specifically for parting operations. Drilling is accomplished by a drill bit which is a multi edged tool. Knurling is performed by the knurling tool with its forming rolls, as previously described.

Boring Operations and Boring Machines:

Boring is a machining operation that enlarges a hole made previously by some other process or produces circular internal profiles in hollow workpieces. The cutting tools used in boring are similar to those used in turning and are mounted on a boring bar to reach the full length of the bore. Boring is essentially an internal turning operation, using a single point tool against a rotating work part with the difference being that boring is performed on the inside diameter of an existing hole rather than the outside diameter of an existing cylinder.

Boring Bar Design and Requirements:

The boring bar must be sufficiently stiff to minimize tool deflection and thus maintain dimensional accuracy and avoid vibration and chatter. For this reason, a material with a high elastic modulus such as tungsten carbide is desirable for boring bar construction. Cemented carbide boring bars have a modulus of elasticity approaching 620 × 10³ MPa, providing the rigidity necessary for precise internal machining. Boring bars have been designed and built with capabilities for damping vibration further improving performance in demanding applications where stability is critical.

Boring Machines and Configurations:

Boring operations on relatively small workpieces can be carried out on lathes while large workpieces are machined on boring mills. These machine tools are either horizontal or vertical and are capable of performing various operations such as turning, facing, grooving and chamfering. In horizontal boring machines, the workpiece is mounted on a table that can move horizontally in both the axial and radial directions. The cutting tool is mounted on a spindle that rotates in the headstock, which is capable of both vertical and longitudinal movements. Drills, reamers, taps and milling cutters also can be mounted on the machine spindle increasing the versatility of the machine.

A vertical boring mill is similar to a lathe has a vertical axis of workpiece rotation, and can accommodate workpieces with diameters as much as 2.5 meters. The cutting tool is usually a single point made of M2 or M3 high speed steel or P10 (C7) or P01 (CS) carbide. It is mounted on the tool head, which is capable of vertical movement for boring and turning and radial movement for facing guided by the cross rail. The head can be swiveled to produce conical (tapered) holes. Cutting speeds and feeds for boring are similar to those for turning.

Horizontal and Vertical Boring Details:

In a horizontal boring operation, the setup can be arranged in either of two ways. The first setup is one in which the work is fixtured to a rotating spindle, and the tool is attached to a cantilevered boring bar that feeds into the work. The boring bar in this setup must be very stiff to avoid deflection and vibration during cutting. The second possible setup is one in which the tool is mounted to a boring bar and the boring bar is supported and rotated between centers. The work is fastened to a feeding mechanism that feeds it past the tool, and this setup can be used to perform a boring operation on a conventional engine lathe.

A vertical boring machine is used for large, heavy work parts with large diameters, usually where the work part diameter is greater than its length. The part is clamped to a worktable that rotates relative to the machine base with worktables up to 40 feet in diameter available. The typical boring machine can position and feed several cutting tools simultaneously. The tools are mounted on tool heads that can be fed horizontally and vertically relative to the worktable. One or two heads are mounted on a horizontal cross-rail assembled to the machine tool housing above the worktable. The cutting tools mounted above the work can be used for facing and boring. In addition to the tools on the cross rail, one or two additional tool heads can be mounted on the side columns of the housing to enable turning on the outside diameter of the work.

Boring Machine Capabilities and Features:

The tool heads used on a vertical boring machine often include turrets to accommodate several cutting tools which results in a loss of distinction between this machine and a vertical turret lathe. Some machine tool builders make the distinction that the vertical turret lathe is used for work diameters up to 2.5 meters while the vertical boring mill is used for larger diameters. Also vertical boring mills are often applied to one of a kind jobs while vertical turret lathes are used for batch production.

Boring machines are available with a variety of features. Machine capacities range up to 150 kW and are available with computer numerical controls, allowing all movements of the machine to be programmed. Little operator involvement is required and consistency and productivity are improved significantly. Boring machines can be obtained with varying levels of automation and sophistication to match production requirements.

Drilling Operations and Related Processes:

Drilling is a machining operation used to create a round hole in a work part. This contrasts with boring which can only be used to enlarge an existing hole. Most drilling operations are performed using a rotating cylindrical tool that has two cutting edges on its working end. The tool is called a drill or drill bit with the most common form being the twist drill. The rotating drill feeds into the stationary work part to form a hole whose diameter is equal to the drill diameter. Drilling is customarily performed on a drill press although other machine tools also perform this operation.

Design Considerations for Drilling:

The basic design guidelines for drilling include several important considerations. Designs should allow holes to be drilled on flat surfaces and perpendicular to the drill motion. Otherwise the drill tends to deflect and the hole will not be located accurately. Exit surfaces for the drill also should be flat to prevent damage to the drill and ensure proper hole quality. Interrupted hole surfaces should be avoided or minimized for improved dimensional accuracy, for extended drill life and to avoid vibrations that can affect tool life and hole quality.

Hole bottoms should match, if possible, standard drill point angles, while flat bottoms or odd shapes should be avoided as they can cause drill wandering and breakage. Through holes are preferred over blind holes because they allow better chip evacuation and easier machining. If holes with large diameters are required, the workpiece should have a preexisting hole, preferably made during fabrication of the part by processes such as casting, powder metallurgy, or forming. Dimples should be provided when preexisting holes are not practical in order to reduce the tendency of the drill to walk during initial engagement. Parts should be designed so that all drilling can be performed with a minimum of fixturing and without having to reposition the workpiece, which reduces setup time and improves accuracy. Blind holes must be drilled deeper than subsequent reaming or tapping operations that may be performed to accommodate the tooling and allow for proper chip accumulation.

Operations Related to Drilling:

Several operations related to drilling are performed to modify or enhance holes after initial drilling. Most of these operations follow drilling where a hole must be made first by drilling and then the hole is modified by one of the other operations. Centering and spot facing are exceptions to this rule as they can be performed before drilling. All of these operations use rotating tools. Reaming is used to slightly enlarge a hole to provide a better tolerance on its diameter, and to improve its surface finish. The tool is called a reamer, and it usually has straight flutes. For soft metals a reamer typically removes a minimum of 0.2 millimeters on the diameter of a drilled hole, while for harder metals, about 0.13 millimeters is removed. Attempts to remove smaller layers can be detrimental, as the reamer may be damaged or the hole surface may become burnished. In this case, honing would be preferred. In general, reamer speeds are one half those of the same size drill and three times the feed rate.

Tapping is performed by a tap and is used to provide internal screw threads on an existing hole. Tapping may be done by hand or with machines such as drilling machines, lathes, automatic screw machines and vertical CNC milling machines. Special tapping machines are available with features for multiple tapping operations. Multiple spindle tapping heads are used extensively, particularly in the automotive industry where 30 to 40 percent of machining operations involve the tapping of holes. Counterboring provides a stepped hole in which a larger diameter follows a smaller diameter partially into the hole. A counterbored hole is used to seat a bolt head into a hole so the head does not protrude above the surface. Countersinking is similar to counterboring except that the step in the hole is cone shaped for flat head screws and bolts. Centering, also called center drilling, drills a starting hole to accurately establish its location for subsequent drilling, and the tool is called a center drill. Spot facing is similar to milling and is used to provide a flat machined surface on the work part in a localized area.

Reaming Tools and Applications:

Reaming is an operation used to make an existing hole dimensionally more accurate than can be achieved by drilling alone and to improve its surface finish. The most accurate holes in workpieces generally are produced by the following sequence of operations: centering, drilling, boring and reaming. For even better accuracy and surface finish, holes may be burnished or internally ground and honed. Hand reamers are straight or have a tapered end in the first third of their length. Various machine reamers, also called chucking reamers because they are mounted in a chuck and operated by a machine are available in two types. Rose reamers have cutting edges with wide margins and no relief and they remove considerable material and true up a hole for flute reaming. Fluted reamers have small margins and relief with a rake angle of about 5 degrees and they usually are used for light cuts of about 0.1 millimeter on the hole diameter.

Shell reamers, which are hollow and are mounted on an arbor, generally are used for holes larger than 20 millimeters. Expansion reamers are adjustable for small variations in hole size and also to compensate for wear of the reamer's cutting edges. Adjustable reamers can be set for specific hole diameters and therefore are versatile. Reamers may be held rigidly as in a chuck, or they may float in their holding fixtures to ensure alignment or be piloted in guide bushings placed above and below the workpiece. A further development in reaming consists of the dreamer, a tool that combines drilling and reaming. The tip of the tool produces a hole by drilling and the rest of the same tool performs a reaming operation. A similar development involves drilling and tapping in one stroke using a single tool. Reamers typically are made of high speed steels such as M1, M2, and M7 or solid carbides such as K20 or C2, or have carbide cutting edges. Reamer maintenance and reconditioning are important for hole accuracy and surface finish.

Tapping Operations and Equipment:

Internal threads in workpieces can be produced by tapping. A tap is a chip producing threading tool with multiple cutting teeth. Taps generally are available with two, three, or four flutes. The most common production tap is the two flute spiral point tap which forces the chips into the hole so that the tap needs to be retracted only at the end of the cut. Three fluted taps are stronger because more material is available in the flute. Tap sizes range up to 100 millimeters. Tapered taps are designed to reduce the torque required for the tapping of through holes. Bottoming taps are for tapping blind holes to their full depth. Collapsible taps are used in large diameter holes and after tapping has been completed, the tap is collapsed mechanically and is removed from the hole without rotation. Chip removal can be a significant problem during tapping because of the small clearances involved. If chips aren't removed properly, the excessive torque that results can break the tap. The use of a cutting fluid and periodic reversal and removal of the tap from the hole are effective means of chip removal and of improving the quality of the tapped hole.

For higher tapping productivity, drilling and tapping can be combined in a single operation called drapping with a single tool. The tool has a drilling section at its tip, followed by a tapping section. Tapping may be done by hand or with machines such as drilling machines, lathes, automatic screw machines and vertical CNC milling machines combining the correct relative rotation and the longitudinal feed. Special tapping machines are available with features for multiple tapping operations. With proper lubrication, tap life may be as high as 10,000 holes. Tap life can be determined with the same technique used to measure drill life. Taps usually are made of high speed steels such as M1, M2, M7 and M10. Productivity in tapping operations can be improved by high speed tapping with surface speeds as high as 100 meters per minute. Self reversing tapping systems also have been improved significantly and are now in use with modern computer controlled machine tools. Operating speeds can be as high as 5,000 revolutions per minute although actual cutting speeds in most applications are considerably lower. Cycle times typically are on the order of 1 to 2 seconds. Some tapping systems now have capabilities for directing the cutting fluid to the cutting zone through the spindle and a hole in the tap which also helps flush the chips out of the hole being tapped. Chipless tapping is a process of internal thread rolling using a forming tap.

Drilling Machines and Workholding:

Drilling machines are used for drilling holes, tapping, reaming, and small diameter boring operations. The most common machine is the drill press, the major components of which include the base, column, table and spindle. The workpiece is placed on an adjustable table either by clamping it directly into the slots and holes on the table or by using a vise which in turn is clamped to the table. The drill is lowered manually by a handwheel or by power feed at preset rates. Manual feeding requires some skill in judging the appropriate feed rate. Drill presses usually are designated by the largest workpiece diameter that can be accommodated on the table and typically range from 150 to 1,250 millimeters. In order to maintain proper cutting speeds at the cutting edges of drills, the spindle speed on drilling machines has to be adjustable to accommodate different drill sizes. Adjustments are made by means of pulleys, gearboxes or variable speed motors.

The types of drilling machines range from simple bench type drills used to drill small diameter holes to large radial drills which can accommodate large workpieces. The distance between the column and the spindle center can be as much as 3 meters. The drill head of universal drilling machines can be swiveled to drill holes at an angle. Developments in drilling machines include numerically controlled three axis machines in which the operations are performed automatically and in the desired sequence with the use of a turret that holds several different drilling tools. Drilling machines with multiple spindles, called gang drilling, are used for high production rate operations. These machines are capable of drilling, in one cycle, as many as 50 holes of varying sizes, depths and locations. They also are used for reaming and counterboring operations. However, with advances in machine tools, gang drilling machines are now being replaced with numerical-control turret drilling machines.

Special drilling machines, such as those which produce holes in continuous hinges or piano hinges use twist drills 1 millimeter in diameter. These machines usually are horizontal and produce holes in up to 3 meter long segments in one cycle. Workholding devices for drilling are essential to ensure that the workpiece is located properly. They also keep the workpiece from slipping or rotating during drilling. Workholding devices are available in various designs, with important features being three point locating for accuracy and three dimensional workholding for secure fixtures.

Milling Operations and Milling Machines:

Milling is a machining operation in which a work part is fed past a rotating cylindrical tool with multiple cutting edges. In rare cases, a tool with one cutting edge called a fly cutter is used. The axis of rotation of the cutting tool is perpendicular to the direction of feed, and this orientation between the tool axis and the feed direction is one of the features that distinguishes milling from drilling. In drilling, the cutting tool is fed in a direction parallel to its axis of rotation. The cutting tool in milling is called a milling cutter and the cutting edges are called teeth.

The geometric form created by milling is a plane surface although other work geometries can be created either by means of the cutter path or the cutter shape. Owing to the variety of shapes possible and its high production rates, milling is one of the most versatile and widely used machining operations. Milling is an interrupted cutting operation, meaning the teeth of the milling cutter enter and exit the work during each revolution. This interrupted cutting action subjects the teeth to a cycle of impact force and thermal shock on every rotation requiring the tool material and cutter geometry to be designed to withstand these conditions.

Types of Milling Operations:

There are two basic types of milling operations: peripheral milling and face milling. Most milling operations create geometry by generating the shape.

In peripheral milling also called plain milling, the axis of the tool is parallel to the surface being machined and the operation is performed by cutting edges on the outside periphery of the cutter. Several types of peripheral milling include slab milling, the basic form of peripheral milling in which the cutter width extends beyond the workpiece on both sides. Slotting also called slot milling, occurs when the width of the cutter is less than the workpiece width, creating a slot in the work. When the cutter is very thin, this operation can be used to mill narrow slots or cut a work part in two called saw milling. Side milling uses the cutter to machine the side of the workpiece. Straddle milling is the same as side milling, only cutting takes place on both sides of the work. Form milling uses milling teeth that have a special profile that determines the shape of the slot that is cut in the work and it is therefore classified as a forming operation.

In peripheral milling, the direction of cutter rotation distinguishes two forms of milling: up milling and down milling. In up milling also called conventional milling, the direction of motion of the cutter teeth is opposite the feed direction when the teeth cut into the work which means it is milling against the feed. In down milling also called climb milling, the direction of cutter motion is the same as the feed direction when the teeth cut the work meaning it is milling with the feed.

In face milling, the axis of the cutter is perpendicular to the surface being milled, and machining is performed by cutting edges on both the end and outside periphery of the cutter. As in peripheral milling, various forms of face milling exist. Conventional face milling occurs when the diameter of the cutter is greater than the work part width, so the cutter overhangs the work on both sides. Partial face milling occurs where the cutter overhangs the work on only one side. End milling uses a cutter diameter less than the work width, so a slot is cut into the part. Profile milling is a form of end milling used to cut the outside periphery of a flat part. Pocket milling is another form of end milling used to mill shallow pockets into flat parts. Surface contouring uses a ball nose cutter rather than square end cutter, fed back and forth across the work along a curvilinear path at close intervals to create a three dimensional surface form. The same basic cutter control is required to machine the contours of mold and die cavities in which case the operation is called die sinking.

Milling Machine Types and Configurations:

Milling machines must provide a rotating spindle for the cutter and a table for fastening, positioning and feeding the work part. Various machine tool designs satisfy these requirements. Milling machines can be classified as horizontal or vertical. A horizontal milling machine has a horizontal spindle and this design is well suited for performing peripheral milling such as slab milling, slotting, side and straddle milling on work parts that are roughly cube shaped. A vertical milling machine has a vertical spindle and this orientation is appropriate for face milling, end milling, surface contouring and die sinking on relatively flat work parts.

Beyond spindle orientation, milling machines can be classified into the following types: knee and column, bed type, planer type, tracer mills and CNC milling machines. The knee and column milling machine is the basic machine tool for milling deriving its name from the fact that its two main components are a column that supports the spindle and a knee that supports the worktable. It is available as either a horizontal or a vertical machine. In the horizontal version, an arbor usually supports the cutter, and the arbor is basically a shaft that holds the milling cutter and is driven by the spindle. An overarm is provided on horizontal machines to support the arbor. On vertical knee and column machines, milling cutters can be mounted directly in the spindle without an arbor.

One of the features of the knee and column milling machine that makes it so versatile is its capability for worktable feed movement in any of the x-y-z axes. The worktable can be moved in the x-direction, the saddle can be moved in the y-direction, and the knee can be moved vertically to achieve the z-movement. Two special knee-and-column machines should be identified. The universal milling machine has a table that can be swiveled in a horizontal plane about a vertical axis to any specified angle, which facilitates the cutting of angular shapes and helixes on work parts. The ram mill has the toolhead containing the spindle located on the end of a horizontal ram and the ram can be adjusted in and out over the worktable to locate the cutter relative to the work. The toolhead can also be swiveled to achieve an angular orientation of the cutter with respect to the work, providing considerable versatility in machining a variety of work shapes.

Bed type milling machines are designed for high production and are constructed with greater rigidity than knee and column machines, thus permitting them to achieve heavier feed rates and depths of cut needed for high material removal rates. The characteristic construction of the bed type milling machine has the worktable mounted directly to the bed of the machine tool rather than using the less rigid knee type design. This construction limits the possible motion of the table to longitudinal feeding of the work past the milling cutter. The cutter is mounted in a spindle head that can be adjusted vertically along the machine column. Single spindle bed machines are called simplex mills and are available in either horizontal or vertical models. Duplex mills use two spindle heads usually positioned horizontally on opposite sides of the bed to perform simultaneous operations during one feeding pass of the work. Triplex mills add a third spindle mounted vertically over the bed to further increase machining capability.

Planer type mills are the largest milling machines with general appearance and construction resembling a large planer. The difference is that milling is performed instead of planing so one or more milling heads are substituted for the single point cutting tools used on planers and the motion of the work past the tool is a feed rate motion rather than a cutting speed motion. Planer mills are built to machine very large parts with the worktable and bed heavy and relatively low to the ground, and the milling heads supported by a bridge structure that spans across the table.

A tracer mill also called a profiling mill is designed to reproduce an irregular part geometry that has been created on a template. Using either manual feed by a human operator or automatic feed by the machine tool, a tracing probe is controlled to follow the template while a milling head duplicates the path taken by the probe to machine the desired shape. Tracer mills are of two types: x-y tracing in which the contour of a flat template is profile milled using two axis control, and x-y-z tracing, in which the probe follows a three dimensional pattern using three axis control. Tracer mills have been used for creating shapes that cannot easily be generated by a simple feeding action of the work against the milling cutter with applications including molds and dies. In recent years, many of these applications have been taken over by computer numerical control milling machines.

Shaping and Planing Operations:

Shaping and planing are similar operations both involving the use of a single point cutting tool moved linearly relative to the work part. In conventional shaping and planing, a straight, flat surface is created by this action. The difference between the two operations is that in shaping, the speed motion is accomplished by moving the cutting tool, while in planing, the speed motion is accomplished by moving the work part. Cutting tools used in shaping and planing are single point tools. Unlike turning, interrupted cutting occurs in shaping and planing subjecting the tool to an impact loading upon entry into the work. In addition, these machine tools are limited to low speeds due to their start and stop motion. These conditions normally dictate the use of high speed steel cutting tools.

Shaping Operations:

Shaping is performed on a machine tool called a shaper. The components of the shaper include a ram, which moves relative to a column to provide the cutting motion, and a worktable that holds the part and accomplishes the feed motion. The motion of the ram consists of a forward stroke to achieve the cut and a return stroke during which the tool is lifted slightly to clear the work and then reset for the next pass. On completion of each return stroke, the worktable is advanced laterally relative to the ram trajectory to feed the part. Feed is specified in millimeters per stroke or inches per stroke. The drive mechanism for the ram can be either hydraulic or mechanical. Hydraulic drive provides greater flexibility in adjusting the stroke length and a more uniform speed during the forward stroke but it is more expensive than a mechanical drive unit. Both mechanical and hydraulic drives are designed to achieve higher speeds on the return noncutting stroke than on the forward cutting stroke thereby increasing the proportion of time spent cutting.

Planing Operations:

The machine tool for planing is a planer, where cutting speed is achieved by a reciprocating worktable that moves the part past the single point cutting tool. The construction and motion capability of a planer permit much larger parts to be machined than on a shaper. Planers can be classified as open side planers or double-column planers. The open side planer, also known as a single column planer has a single column supporting the cross rail on which a toolhead is mounted. Another toolhead can also be mounted and fed along the vertical column. Multiple toolheads permit more than one cut to be taken on each pass. At the completion of each stroke each toolhead is moved relative to the cross rail or column to achieve the intermittent feed motion. The configuration of the open side planer permits very wide work parts to be machined.

A double column planer has two columns, one on either side of the base and worktable. The columns support the cross rail, on which one or more toolheads are mounted. The two columns provide a more rigid structure for the operation however the two columns limit the width of the work that can be handled on this machine. Shaping and planing can be used to machine shapes other than flat surfaces with the restriction that the cut surface must be straight. This allows the cutting of grooves, slots, gear teeth and other shapes. Special machines and tool geometries must be specified to cut some of these shapes. An important example is the gear shaper, a vertical shaper with a specially designed rotary feed table and synchronized tool head used to generate teeth on spur gears.

Broaching Operations and Broaching Machines:

Broaching is similar to shaping with a long multiple tooth cutter and is used to machine internal and external surfaces such as holes of circular, square or irregular section, keyways, the teeth of internal gears, multiple spline holes and flat surfaces. In a broach, the total depth of material removed in one stroke is the sum of the depths of cut of each tooth of the broach. A large broach can remove material as deep as 38 millimeters in one stroke. Broaching is performed using a multiple teeth cutting tool by moving the tool linearly relative to the work in the direction of the tool axis. The machine tool is called a broaching machine and the cutting tool is called a broach. For certain jobs for which broaching can be used, it is a highly productive method of machining with advantages including good surface finish, close tolerances and a variety of work shapes. Owing to the complicated and often custom-shaped geometry of the broach, tooling is expensive. Broaching is an important production process and can produce parts with good surface finish and dimensional accuracy, competing favorably with other processes such as boring, milling, shaping and reaming to produce similar shapes. Although broaches can be expensive, the cost is justified with high quantity production runs.

Types of Broaching:

There are two principal types of broaching: external also called surface broaching and internal. External broaching is performed on the outside surface of the work to create a certain cross sectional shape on the surface. Internal broaching is accomplished on the internal surface of a hole in the part requiring a starting hole to be present in the part to insert the broach at the beginning of the broaching stroke.

Broaching Machines:

The machines for broaching are relatively simple in construction, having only linear motions, and are usually actuated hydraulically although some are moved by crank, screw or rack. Many styles of broaching machines are available and sizes range from machines for making needle like parts to those used for broaching gun barrels including rifled gun barrels with internal spiral grooves.

Broaching machines either pull or push the broaches and are either horizontal or vertical. Push broaches usually are shorter, generally in the range from 150 to 350 millimeters. Pull broaches tend to straighten the hole whereas pushing permits the broach to follow any irregularity of the leader hole. Horizontal machines are capable of longer strokes.

Most broaching machines can be classified as either vertical or horizontal. The vertical broaching machine is designed to move the broach along a vertical path while the horizontal broaching machine has a horizontal tool path. Most broaching machines pull the broach past the work. However there are exceptions to this pull action. One exception is a relatively simple type called a broaching press, used only for internal broaching, that pushes the tool through the work part. Another exception is the continuous broaching machine in which the work parts are fixtured to an endless belt loop and moved past a stationary broach. Because of its continuous operation, this machine can be used only for surface broaching. The force required to pull or push the broach depends on the strength of the workpiece material, total depth and width of cut, cutting speed, tooth profile and use of cutting fluids. The pulling force capacities of broaching machines are as high as 0.9 MN.

Sawing Operations:

Sawing is a process in which a narrow slit is cut into the work by a tool consisting of a series of narrowly spaced teeth. Sawing is normally used to separate a work part into two pieces or to cut off an unwanted portion of a part. These operations are often referred to as cutoff operations. Since many factories require cutoff operations at some point in the production sequence sawing is an important manufacturing process. In most sawing operations, the work is held stationary and the saw blade is moved relative to it. There are three basic types of sawing according to the type of blade motion involved: hacksawing, bandsawing and circular sawing.

Hacksawing:

Hacksawing involves a linear reciprocating motion of the saw against the work and is often used in cutoff operations. Cutting is accomplished only on the forward stroke of the saw blade. Because of this intermittent cutting action, hacksawing is inherently less efficient than the other sawing methods both of which are continuous. The hacksaw blade is a thin straight tool with cutting teeth on one edge. Hacksawing can be done either manually or with a power hacksaw that provides a drive mechanism to operate the saw blade at a desired speed and also applies a given feed rate or sawing pressure.

Bandsawing:

Bandsawing involves a linear continuous motion using a bandsaw blade made in the form of an endless flexible loop with teeth on one edge. The sawing machine is a bandsaw which provides a pulley like drive mechanism to continuously move and guide the bandsaw blade past the work. Bandsaws are classified as vertical or horizontal with the designation referring to the direction of saw blade motion during cutting. Vertical bandsaws are used for cutoff as well as other operations such as contouring and slotting. Contouring on a bandsaw involves cutting a part profile from flat stock. Slotting is the cutting of a thin slot into a part an operation for which bandsawing is well suited. Contour sawing and slotting are operations in which the work is fed into the saw blade.

Vertical bandsaw machines can be operated either manually where the operator guides and feeds the work past the bandsaw blade or automatically, where the work is power fed past the blade. Recent innovations in bandsaw design have permitted the use of CNC to perform contouring of complex outlines. Horizontal bandsaws are normally used for cutoff operations as alternatives to power hacksaws.

Circular Sawing and Related Processes:

Circular sawing uses a rotating saw blade to provide a continuous motion of the tool past the work and is often used to cut long bars, tubes and similar shapes to specified length. The cutting action is similar to a slot milling operation, except that the saw blade is thinner and contains many more cutting teeth than a slot milling cutter. Circular sawing machines have powered spindles to rotate the saw blade and a feeding mechanism to drive the rotating blade into the work. Two operations related to circular sawing are abrasive cutoff and friction sawing. In abrasive cutoff, an abrasive disk is used to perform cutoff operations on hard materials that would be difficult to saw with a conventional saw blade. In friction sawing, a steel disk is rotated against the work at very high speeds, resulting in friction heat that causes the material to soften sufficiently to permit penetration of the disk through the work. The cutting speeds in both of these operations are much faster than in circular sawing.

The comprehensive range of machining processes available to modern manufacturing provides exceptional capability to produce components with precise dimensions, surface finishes and geometric features. From the fundamental turning operations on lathes to specialized processes like broaching and sawing each method offers distinct advantages and applications. Turning operations on lathes offer versatility in producing cylindrical, conical and contoured workpieces using single point and form tools. Boring extends these capabilities to internal surfaces with specialized machines accommodating workpieces up to 2.5 meters in diameter and power capacities reaching 150 kW. Drilling creates holes with subsequent operations like reaming, tapping, counterboring and countersinking enhancing accuracy and functionality.

Milling provides one of the most versatile and widely used machining processes, capable of producing flat surfaces, slots, contours and complex three dimensional shapes through peripheral and face milling operations on various machine configurations. Shaping and planing offer straightforward methods for creating flat surfaces and straight grooves with planers accommodating exceptionally large workpieces. Broaching delivers high productivity with excellent surface finish and close tolerances for both internal and external shapes, justifying expensive tooling costs through high quantity production runs. Sawing operations, including hacksawing, bandsawing and circular sawing provide efficient cutoff and contouring capabilities essential throughout the manufacturing sequence.