Manufacturing and engineering workshops require lathe machines as their essential tool for cutting cylindrical workpieces. These machines operate effectively for multiple metal processing tasks, covering turning, facing, grooving, and chamfering, with other applications for making exact parts.
The modern CNC lathe features automation through tool changers that enable the machine to switch between different tools according to operational requirements. To maximize metal removal rates and achieve precision dimensions alongside high-quality surface finishes in machined products, one must choose appropriate lathe tools.
The following article presents an introduction to 15 typical lathe tools applied on CNC turning centers, along with their essential characteristics and employment purposes.
The external turning tool functions as the external grooving tool and OD (outside diameter) turning tool, which stands as the most common instrument within CNC lathes. The external turning tool operates by eliminating material on the outer component of turning cylindrical parts aligned within the spindle to reach specified dimensions.
The insert on an external turning tool features a sharp cutting edge ground at specific angles designed to shear away metal chips with minimum cutting forces. By advancing the tool perpendicularly towards the workpiece with each pass, precise amounts of material can be removed to achieve target diameters. These tools are available with various insert shapes like triangular, rhombic, square, round, and others.
External turning operations also produce excellent surface finishes determined by tool geometry factors like lead angle, rake angle, and nose radius. CNC programmers optimize cutting parameters like speed, feed rate, and depth of cut based on workpiece material so that the tool engages it efficiently during roughing and finishing passes.
While external turning tools machine outside surfaces, internal turning tools, also called boring bars, operate on the inner surfaces of cylindrical workpieces. They are designed to cut grooves, holes, and other internal features with precision dimensions and low surface roughness.
These tools consist of a long barrel that enables them to access the interior of workpieces mounted on the lathe spindle. Cutting forces are transmitted through the bar, which must be rigid enough not to deflect during machining. The internal turning tool insert features geometries optimized for shearing metal and handling cutting loads involved during boring.
By combining longitudinal and crosswise interpolation movements, CNC lathes equip internal turning tools to produce holes with very tight tolerances. In addition to simple through holes, these tools can also create precise patterns, such as trepanning, shapes, grooves, and undercuts, on inner diameters based on programmed tool paths.
The boring bar is a type of internal turning tool specialized for precisely sizing, finishing, or enlarging existing holes. It plays a key role in accurate hole machining applications needed in automotive, aerospace, and other engineering components.
Rigid boring bars minimize deflection, which is vital for true boring results and the roundness of holes. They allow large overhangs inside deep holes to increase cutting access. Boring bars also come with specialized insert geometries that enable shearing the material efficiently, even at low cutting speeds associated with their use.
CNC lathes deploy boring bars for achieving stringent hole size, finish, and positional tolerances unattainable with conventional drilling or reaming, but required in critical parts. Boring also eliminates the distortion or misalignment present in pre-drilled holes. Machinists have to carefully select boring feed rates and cutting depths to get the expected dimensional precision and surface quality of finished holes.
The parting tool, also called a grooving tool, performs an important operation on CNC lathes of separating finished workpieces from the excess material, also known as remnant. It cuts deep, narrow grooves around the workpiece using its sharp insert to facilitate breaking off or ‘parting’ the finished part eventually.
These tools have advanced geometries and suitable angles that enable smooth penetration even through tough materials with continuous chips. By applying sufficient pressure on the tool, deep grooves approaching the workpiece center can be produced progressively until remnants get fractured at the bottom surface.
Parting tools for CNC applications feature optimal clearances, chip breakers, heat dissipation design, and strength to withstand large cutting forces involved during this severing process. Rigid tool holding interfaces also play a vital role in minimizing deflection. With appropriate speed and feed settings, parting tools deliver high repeatability and consistent groove dimensions.
Facing tools, also called end mills, have a vital role on CNC lathes to accurately machine workpiece ends perpendicular to the turning axis. This facing operation prepares one end with a smooth surface and establishes the workpiece length to the exact size required before external or internal features are machined.
The facing tool insert features geometries suitable for end cutting operations. It machines away material in successive axial passes with a small width of cut and rapidly generates smooth, flat surfaces. Appropriate rake angles on the cutting edge provide easy chip formation to prevent work hardening on the delicate workpiece edge.
CNC programmers determine the facing feed rate, speed, and depth parameters based on the hardness of the workpiece material. Coolants are often deployed to minimize temperature rise during facing and avoid undue dimensional errors. Facing tools establish workpiece geometry, ensuring subsequent operations like drilling, boring, grooving, etc. give accurate results.
Thread cutting on internal or external surfaces is a common requirement on precision turned workpieces for assembly or fastening purposes. Specialized threading tools on CNC lathes cut accurate helical grooves or threads using single-point insert cutters based on the programmed pitch and depth.
The thread cutting insert features suitable geometry angles needed for gradually removing material with each pass to generate V-shaped threads with the correct profile. Thread turning tools come with inserts for cutting metric, UNF, UNC, or other standard thread forms as per component design needs.
CNC systems enable threading tools to produce threads precisely matched to thread gauges or mating parts. In addition to conventional 60° threads, the Acme, buttress, and other types can also be accurately cut on CNC lathes based on a tool path strategy. Coolants prevent built-up edge and improve thread finish.
Knurling is an important secondary operation performed on lathe-machined components to create a patterned indentation layer on the surface for an enhanced grip. Common examples include the grip areas on nuts, handles, controls, etc., where tactile friction is required for operation without slippage.
The knurling tool consists of a single or double row of sharp pyramidal cutting teeth that can imprint a precise diamond, straight, or other aesthetic pattern on the workpiece. By feeding the tool perpendicular to the job and applying pressure, the teeth displace material and cold form the required knurled texture.
CNC knurling processes allow excellent control over pattern dimensions and depth consistency unattainable with manual methods. Different knurl patterns can be produced on a single workpiece by changing tools. In addition to visual appeal and tactile function, knurling also serves to hide machining marks below the embossed pattern.
Grooving is used on CNC turned components to produce external or internal circumferential grooves for various applications. These include seating O-rings for sealing functions, creating partitions, retaining ring grooves, oil reservoirs, etc., based on component design needs.
Grooving tools consist of compact cutter heads equipped with indexable inserts and are available in different widths. By interpolating the tool in a direction parallel to the workpiece axis, narrow grooves with square or radiused bottom profiles can be accurately cut.
Common groove dimensions range from 1-6 mm in width and up to 5 mm in depth. The grooving inserts feature suitable lead angles, chip breakers, and other geometry factors to generate continuous chips when machining axially or radially. Grooving and parting tools share several design aspects optimized for such deep, heavy-duty operations.
Components with sharp edges or corners often need targeted edge preparation or ‘chamfering’ to serve functional or safety needs. For example, a chamfer removes hazardous sharp edges or provides a lead-in for easier assembly of mating parts. It also minimizes corner stresses, preventing crack initiation.
Chamfering tools deploy indexable inserts with suitable geometry to produce precision edge preparation. By interpolating along the workpiece corners, they uniformly bevel edges in a highly repeatable manner. Common chamfer types like 30°, 45°, or customized angles can be readily produced on CNC systems based on part requirements.
Chamfer milling on lathes also improves edge finish and deburrs exit burrs if present. This prevents cutting hands during subsequent handling while enhancing aesthetic appeal. For critical applications, CNC chamfering ensures every workpiece edge gets uniformly machined, eliminating the variability of manual deburring processes.
Forming tools equip CNC lathes with the special capability of producing complex, non-cylindrical profiles not possible with conventional turning inserts. They come with full form inserts featuring the mirror image of the desired workpiece profile and work by pressing this shape onto the rotating blank.
Form turning employs a combination of optimized feed rates and depth of cut to uniformly displace material across the profile until the desired intricate form geometry is duplicated on the workpiece. No metal cutting takes place, but shearing combined with cold working deforms it precisely into the preformed shape.
Diamond or other polycrystalline inserts prevent wear during the high-pressure forming action needed for these operations. Using suitable tool holding rigidity and process parameters, forming tools help shorten manufacturing cycles of complex parts by consolidating multiple fabrication steps.
CNC turning centers frequently incorporate powerful drilling capability to drill holes as part of sequential machining operations on a workpiece. Drill tools help eliminate the need for dedicated drilling machines, saving workflow time and improving accuracy.
Drills with indexable carbide inserts are commonly used for holemaking on CNC lathes. They provide high cutting speeds along with the rigidity required for maintaining positional accuracy of holes. Coolant ports in tool bodies improve chip evacuation and prevent built-up edges during drilling.
Powerful programmable spindle motors also enable drilling tools to bore deep holes with straightness and surface finish adhering to precision component requirements. CNC systems optimize feeds, speeds, and peck drilling cycles based on hole diameter and depth values. Automated in-process gaging checks further improve quality control.
The reaming operation serves a vital finishing purpose on CNC lathes to improve the accuracy and surface finish quality of pre-bored holes. It finely enlarges the hole size while smoothing out any residual errors left over from initial drilling processes.
Reamers are precision tools with very tight diameter tolerances used at low speeds to deliver highly accurate hole dimensions. They cut only a few thousandths of an inch during a reaming pass, eliminating distortion risk while finishing holes. High rigidity is vital to prevent chattering marks from being transferred onto the hole surface.
CNC reaming procedures enhance hole size precision to levels unattainable with drilling alone. This facilitates smooth insertion of bearing shafts or mating components with precision interference fits. Reamed holes also have improved roundness and cylindricity, meeting critical application needs.
Many lathe-turned workpieces feature tapered diameters that gradually reduce along the turning axis for specialized applications. Taper turning tools specialize in machining precise external or internal tapers on CNC lathes using coordinated interpolation motions.
These single-point cutting tools deploy inserts with optimized edge preparation to handle the continuous depth changes encountered when shaping conical geometries. Taper turning involves simultaneous coordination of axial feed for diameter reduction and radial feed for roughing/finishing along the cone’s length.
In addition to straight tapers, CNC programs can also generate complex profiles with curved or stepped tapers using suitable tool paths. By creating custom tool vectors, irregular tapers needed for specific part designs can be produced without needing specially formed tools or manual setups.
Thread milling has emerged as an efficient alternative to single-point thread turning methods for producing threads, especially for large batch production scenarios. Thread mills feature inserts with formed teeth that replicate the thread profile and employ interpolating axial movements for generating threads via a milling process.
Thread mills are available in different sizes capable of cutting a range of metric or inch thread forms and pitches. They provide higher productivity than turning and better consistency over several workpieces. Thread milling also eliminates the need for custom tools when changing threads on adaptable CNC lathes.
Advanced CNC programs determine optimum feed rates and spindle speeds for thread milling operations based on thread pitch, part material hardness, cutter diameters, etc. Coolants prevent built-up edges, ensuring clean, uninterrupted threads over long production runs.
Broaching tools contain multiple cutting teeth designed for removing material in a precise sequence using a series of light cuts. They are deployed on CNC lathes for cutting internal keyways or splines needing tight size and surface finish specifications.
Each broaching tooth features successively taller dimensions optimized for shearing away a small layer of material in line with keyway/spline dimensions. Broaches provide high accuracy unattainable with other milling methods while finishing intricate forms.
CNC broaching processes enhance productivity using optimized machine settings for rapid metal removal without tool overload. They also enable executing the progressive broaching operation automatically with high repeatability. Broached internal profiles have precision fits for locating pins, shafts, and gears without play or backlash errors.
In this article, we covered some of the most common CNC turning tools encountered in precision production machining applications, ranging from simple facing and turning to complex internal broaching operations. Understanding the unique geometries and working principles of these lathe cutting tools provides vital insights into selecting the right option for different machining requirements.
Optimizing operating parameters in line with tool capabilities and workpiece materials is key to maximizing productivity. Developments in cutting tool materials, coatings, and indexable insert designs continue expanding the scope of operations possible on modern CNC lathes. This consolidates multiple processes in one setup, giving flexible, accurate, and cost-effective solutions.
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