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Indexing head
Indexing head
Indexing head
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Indexing head and tailstock set up on a milling machine's table.

An indexing head, also known as a dividing head or spiral head,[1] is a specialized tool that allows a workpiece to be circularly indexed; that is, easily and precisely rotated to preset angles or circular divisions. Indexing heads are usually used on the tables of milling machines, but may be used on many other machine tools including drill presses, grinders, and boring machines. Common jobs for a dividing head include machining the flutes of a milling cutter, cutting the teeth of a gear, milling curved slots, or drilling a bolt hole circle around the circumference of a part.[2]

The tool is similar to a rotary table except that it is designed to be tilted as well as rotated and often allows positive locking at finer gradations of rotation, including through differential indexing. Most adjustable designs allow the head to be tilted from 10° below horizontal to 90° vertical, at which point the head is parallel with the machine table.

The workpiece is held in the indexing head in the same manner as a metalworking lathe. This is most commonly a chuck but can include a collet fitted directly into the spindle on the indexing head, faceplate, or between centers. If the part is long then it may be supported with the help of an accompanying tailstock.

Manual indexing heads

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Cross-section of an indexing head
Interchangeable indexing plates
A dividing head mounted on the table of a small milling machine. The direct indexing plate and center are visible facing the camera. An interchangeable indexing plate is visible on the left side.

Indexing is an operation of dividing a periphery of a cylindrical workpiece into equal number of divisions by the help of index crank and index plate. A manual indexing head includes a hand crank. Rotating the hand crank in turn rotates the spindle and therefore the workpiece. The hand crank uses a worm gear drive to provide precise control of the rotation of the work. The work may be rotated and then locked into place before the cutter is applied, or it may be rotated during cutting depending on the type of machining being done.

Most dividing heads operate at a 40:1 ratio; that is 40 turns of the hand crank generates 1 revolution of the spindle or workpiece. In other words, 1 turn of the hand crank rotates the spindle by 9 degrees. Because the operator of the machine may want to rotate the part to an arbitrary angle indexing plates are used to ensure the part is accurately positioned.

Direct indexing plate: Most dividing heads have an indexing plate permanently attached to the spindle. This plate is located at the end of the spindle, very close to where the work would be mounted. It is fixed to the spindle and rotates with it. This plate is usually equipped with a series of holes that enables rapid indexing to common angles, such as 30, 45, or 90 degrees. A pin in the base of the dividing head can be extended into the direct indexing plate to lock the head quickly into one of these angles.[3] The advantage of the direct indexing plate is that it is fast and simple, and no calculations are required to use it. The disadvantage is that it can only be used for a limited number of angles.

Interchangeable indexing plates are used when the work must be rotated to an angle not available on the direct indexing plate. Because the hand crank is fixed to the spindle at a known ratio (commonly 40:1) the dividing plates mounted at the handwheel can be used to create finer divisions for precise orientation at irregular angles. These dividing plates are provided in sets of several plates. Each plate has rings of holes with different divisions. For example, an indexing plate might have three rows of holes with 24, 30, and 36 holes in each row. A pin on the hand crank engages these holes. Index plates with up to 400 holes are available.[2] Only one such plate can be mounted to the dividing head at a time. The plate is selected by the machinist based on exactly what angle he wishes to index to.

For example, if a machinist wanted to index (rotate) his workpiece by 22.5 degrees, then he would turn the hand crank two full revolutions plus one-half of a turn. Since each full revolution is 9 degrees and a half-revolution is 4.5 degrees, the total is 22.5 (9 + 9 + 4.5 = 22.5). The one-half turn can easily be done precisely using any indexing plate with an even number of holes and rotating to the halfway point (Hole #8 on the 16-hole ring).

Brown and Sharpe indexing heads include a set of 3 indexing plates. The plates are marked #1, #2 and #3, or "A", "B" and "C". Each plate contains 6 rows of holes. Plate #1 or "A" has 15, 16, 17, 18, 19, and 20 holes. Plate #2 or "B" has 21, 23, 27, 29, 31, and 33 holes. Plate #3 or "C" has 37, 39, 41, 43, 47, and 49 holes.[citation needed]

Universal Dividing heads: some manual indexing heads are equipped with a power drive provision. This allows the rotation of the dividing head to be connected to the table feed of the milling machine instead of using a hand crank. A set of change gears is provided to select the ratio between the table feed and rotation. This setup allows the machining of spiral or helical features such as spiral gears, worms, or screw type parts because the part is simultaneously rotated at the same time it is moved in the horizontal direction. This setup is called a " PTO dividing head".

CNC indexing heads

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CNC indexing heads are similar in design to the manual variety, except that they have a servo motor coupled to the spindle instead of a hand crank and indexing plates. The servo motor is electronically controlled to index the work to the required position. The control can either be a simple keypad for the operator, or it may be fully CNC controlled.

CNC indexing heads may be controlled in two different modes. The most basic method of operation uses simple control functions built into the dividing head. It does not require a CNC machine. The operator enters the desired angle into a control box attached to the indexing head, and it automatically rotates to the desired position and locks into place for machining. Changing angles is as simple as typing a new angle value onto the control pad. This is simpler than setting up a manual indexing head because there is no need to interchange indexing plates or to calculate which hole positions to use. It is also faster for repetitive operations because the work can be indexed by simply pressing a button, eliminating the need to count rotations of the hand crank or specific hole positions on the indexing plate. A CNC dividing head may be used in this manner on either manual or CNC machinery.

Most CNC dividing heads are also able to function as a full CNC axis and may be wired into the control of a CNC machine. This enables the machine's main CNC controller to control the indexing head just like it would control the other axes of the machine. This can be used to machine complex 3D shapes, helices with a non-constant pitch, and similar exotic parts. This mode of operation cannot be used on a manual machine tool because it requires a full CNC controller to operate.

References

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Indexing head

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from Grokipedia
An indexing head, also known as a dividing head, is a specialized accessory designed to provide controlled and repeatable rotational positioning of a workpiece, typically to the table of a milling machine, planer, or shaper. It enables machinists to divide the of a cylindrical or rotational part into precise angular increments, facilitating the creation of evenly spaced features such as gear teeth, splines, or bolt hole patterns. The device operates on a worm-and-worm-wheel mechanism, commonly with a 40:1 gear ratio, where one full turn of the indexing crank advances the spindle by 1/40th of a , allowing for divisions from as few as 2 up to 600 segments depending on the indexing plate used. Key components of an indexing head include the spindle, which holds the workpiece via a or centers; the gear attached to the crank shaft; the wheel that drives the spindle; and interchangeable indexing plates featuring concentric circles of precisely drilled holes (typically in sets covering 15–49 holes) for locking the position with an indexing pin. Additional features often encompass a disengagement for direct drive indexing, a footstock for supporting longer workpieces, and sector arms to track crank handle positions during multi-turn operations. This setup ensures high accuracy, often to within a few minutes of arc, making it indispensable for repetitive precision tasks in . Historically, indexing heads have been integral to manual machining since the late , evolving from simple dividing engines to versatile attachments that enhance the capabilities of universal milling machines. In modern applications, while CNC machines have reduced reliance on manual indexing for production, indexing heads remain valuable for prototyping, education, and custom fabrication where exact manual control is required. Their use extends beyond milling to grinding and even setups, underscoring their role in achieving complex geometries without full automation.

History and Development

Origins in 19th Century Machining

The development of the indexing head emerged in the mid-19th century amid rapid advancements in , closely tied to the innovations of Joseph R. Brown at the firm Manufacturing Company. In 1850, Brown invented America's first linear dividing engine, a device for accurately graduating rules and scales by automating precise linear divisions, which established foundational principles for controlled rotational indexing in machine tools. This invention addressed the need for high-accuracy measurement in growing industrial applications, building on earlier traditions. By the early 1860s, Brown's work extended to rotary applications with the creation of the universal milling machine in 1861, the first of its kind to incorporate a dedicated indexing head for dividing and spiral operations. Delivered to the Providence Tool Company in 1862, this machine used the indexing head to perform tasks such as milling helical flutes on twist drills and cutting gears, significantly enhancing efficiency over manual methods during the Civil War era. The indexing head's gear-driven mechanism allowed for repeatable angular positioning, revolutionizing gear production and complex contouring on workpieces. Before the advent of standalone indexing heads, dividing operations for and polygonal shaping were conducted using rudimentary attachments on primitive lathes and early milling machines, often involving hand-cranked index plates or simple sector arms. These techniques drew direct influence from 18th- and 19th-century clockmaking, where dividing engines enabled precise gear wheel division for timepieces, adapting similar rotary indexing principles to industrial scales. Early manufacturers like Pratt & Whitney also contributed, producing indexing attachments such as the Lincoln Index milling machine in 1861 for use at Samuel Colt’s armory. Brown & Sharpe's precision gear-cutting and dividing engine of 1855 evolved into later commercial units, supporting mass production of standardized components like gears and bolts in factories, where accuracy was essential for assembly-line efficiency.

Evolution and Key Manufacturers

In the early , indexing heads advanced significantly with the introduction of universal dividing heads around the , which incorporated tilting mechanisms to facilitate helical milling and other complex operations. These designs typically featured a standardized 40:1 worm gear ratio, allowing one full turn of the index crank to produce 1/40th of a spindle rotation for precise divisions. Firms like the played a pivotal role, developing swiveling blocks that enabled full vertical revolutions and specialized index plates with hole circles of 24, 30, and 36 positions to support divisions below 40, enhancing accuracy in and spiral work. Key manufacturers shaped the field's progression, beginning with , which pioneered interchangeable index plates in the 1890s to simplify rapid indexing without sector arms, setting a standard for precision tooling. Post-World War II, Ellis Tool & Manufacturing Co., established in 1960, refined dividing heads with robust construction and easy setup features, making them popular for industrial applications. In modern times, companies like Phase II Plus and Grizzly Industrial have produced affordable replicas and variants, often with improved materials and accessories for hobbyists and small shops. By the late , indexing heads began integrating with CNC systems, functioning as programmable rotary axes on CNC mills to improve in high-volume . As of 2025, developments include CNC-compatible dividing heads with stepper motors for enhanced precision in prototyping and retrofits.

Principles of Operation

Basic Mechanism and Worm Gear System

The basic mechanism of an indexing head relies on a worm gear system to achieve precise rotational control of the spindle. A single-thread worm, driven by a hand crank, meshes with a 40-tooth worm wheel affixed to the spindle, establishing a 40:1 gear ratio such that one complete turn of the crank rotates the spindle by 9 degrees (or 1/40 of a full revolution). This configuration ensures high accuracy in angular positioning, with the worm's single thread advancing the worm wheel by one tooth per crank revolution. To facilitate operations requiring unrestricted spindle movement, such as initial setup or direct manual rotation, a disengagement clutch or lever allows the indexing shaft to disconnect from the spindle, enabling free rotation without worm gear influence. Once disengaged, the spindle can be turned by hand and then re-engaged for controlled indexing. In universal indexing heads, the base incorporates a swiveling mechanism that permits tilting of the entire headstock from -10 degrees (below horizontal) to +90 degrees (vertical), accommodating angular workpieces like helical gears or bevels without altering machine setup. This range supports versatile machining orientations while maintaining alignment with the machine table. Backlash prevention is integral to the system's reliability, achieved through adjustable in the worm-wheel to minimize play, the inherent self-locking property of the low-lead-angle worm gear that resists reverse motion under load, and a dedicated spindle lock that secures the assembly during cutting to eliminate vibration-induced movement. These features collectively ensure positional stability, with the worm's tight engagement providing positive resistance to displacement.

Indexing Methods

Direct indexing involves disengaging the worm gear and using the index plate directly to divide the workpiece into a number of equal parts equal to the number of holes in the selected on the plate, typically up to 49 divisions. This method is suitable for simple, low-division tasks like 2, 3, 4, 6, 8, 12, or 24 segments. Simple indexing, also known as plain indexing, utilizes the sector arms and holes in the index plate to achieve divisions of the workpiece into equal parts. In this method, the operator rotates the crank handle connected to the worm gear, advancing the index pin through selected holes on the plate to position the spindle accurately for each division. For instance, to divide a into six equal parts, the crank is turned a specific number of times plus a determined by the plate's hole count, enabling precise angular positioning without additional gearing. Compound indexing extends the capabilities of simple indexing by employing two concentric circles of holes on a single index plate, allowing for finer divisions beyond the standard limits of plain methods, such as creating 127 equal spaces. This technique involves a two-step process where the crank is first rotated relative to one hole circle, followed by repositioning the index plate itself relative to the second circle, effectively multiplying the resolution through nested movements. It is particularly useful for non-standard divisions that cannot be achieved directly, providing greater flexibility in workpiece segmentation. Differential indexing addresses divisions that are not feasible with simple or methods by incorporating a gear train between the index crank and the index plate, which induces a controlled auxiliary in the plate to correct for fractional discrepancies. This adjustment ensures accurate positioning for non-integer relative to the worm gear's fixed , such as dividing into 53 parts, where the gear setup subtly shifts the plate's movement to align with the desired . The method relies on selecting gears that approximate the target division, making it suitable for complex, high-precision tasks despite its setup complexity. Angular indexing enables the setting of arbitrary angles on the workpiece without relying on index plates, using a built-in protractor or graduated scale on the indexing head for direct measurement and rotation of the spindle. This approach is ideal for irregular or non-divisible angles, such as 35 degrees, where the operator swivels or rotates the head to the specified marking and locks it in place. It bypasses the discrete hole-based system, offering versatility for custom angular requirements in operations.

Components and Accessories

Main Structural Parts

The headstock forms the foundational structure of an indexing head, serving as a robust housing for the spindle, worm gear, and crank handle while incorporating a precision-ground base with mounting holes or slots for secure attachment to the T-slots of a milling machine table. This base ensures stability during operation, and the headstock assembly is typically constructed from cast iron to minimize vibration and maintain alignment. The spindle is a precision-machined shaft within the , featuring a tapered bore, such as Morse taper #2 to #4 or taper #7 to #10 depending on the model, to accommodate arbors, chucks, or collets for workpiece attachment, along with a keyway that enables direct drive from the worm gear for rotational control. In some designs, the spindle includes a threaded , such as 1-1/2"-8, for additional accessory mounting, and it is supported by high-quality bearings to ensure smooth, accurate rotation. The index plate carrier is a rotatable component attached to the headstock, designed to hold interchangeable index plates with various hole patterns (for example, plates featuring 15-49 holes) and equipped with a spring-loaded locking pin to secure the selected plate in position. It also incorporates a vernier scale for fine angular adjustments in some designs, allowing precise alignment of the plate relative to the crank mechanism. The crank handle, connected to the worm shaft, provides manual rotation input to the spindle, while the accompanying sector arms—adjustable via cap screws—set limits on the number of crank turns by engaging with the index plate's holes through a spring-loaded , facilitating controlled and repeatable positioning. These arms are calibrated to track fractional rotations, enhancing the accuracy of the indexing process. The integrates with a tailstock for supporting extended workpieces in certain setups.

Workholding and Support Elements

Workholding and support elements are essential attachments for indexing heads, enabling secure fixation and precise positioning of workpieces during rotational operations. These components attach to the indexing head's spindle or auxiliary supports, accommodating various workpiece geometries while maintaining alignment and minimizing deflection. Common options include chucks, collets, centers, dogs, tailstocks, and specialized fixtures, each selected based on the workpiece's shape, size, and material. Chucks provide versatile gripping for a range of workpiece profiles. Three-jaw universal chucks, featuring self-centering jaws, are ideal for round or hexagonal stock, achieving tolerances of 0.002 to 0.003 inches when properly seated. Four-jaw independent chucks, with individually adjustable jaws, suit irregular or square shapes, allowing fine alignment using a dial indicator for high precision. These chucks mount directly to the indexing head's spindle via a threaded backplate or . Collets offer superior accuracy for cylindrical workpieces; spring collets in sets (e.g., 5C type) auto-center round stock up to 1-1/8 inches in diameter with tolerances as tight as 0.0005 inches, while step collets accommodate specific disc-like parts by splitting into sections for custom sizing. For elongated or between-centers holding, centers and dogs facilitate rotation without slippage. Live centers, which revolve with the workpiece via ball bearings, and dead centers, featuring a stationary 60-degree taper point, support the workpiece ends in tandem, with dead centers requiring to prevent overheating. Driving dogs clamp onto the workpiece and engage slots in a faceplate or carrier, transmitting rotational force from the indexing head's spindle while allowing axial freedom. These are particularly effective for long, slender parts to avoid chuck distortion. The tailstock, also known as a footstock, provides adjustable end support opposite the indexing head's spindle, enhancing stability for extended workpieces. It features a with a Morse taper (e.g., #2 or #4) that aligns in height and laterally via a handwheel, with heights ranging from 4 to 8.26 inches depending on the model. This support prevents sagging or vibration during indexing, and its position can be locked firmly to the machine base. Additional fixtures expand versatility for non-cylindrical or complex workpieces. Vises clamp prismatic parts securely to the indexing plate, while clamps and plates secure odd-shaped items via T-slots. Mandrels include solid types with a taper of 0.0005 to 0.0006 inch per inch for precise centering, and expansion mandrels that grip internally by expanding against the bore for true . These elements, often custom-fabricated, ensure adaptability without compromising the indexing head's precision.

Types of Indexing Heads

Plain Indexing Heads

Plain indexing heads feature a fixed horizontal spindle orientation, with the spindle rotating solely about a horizontal axis via a worm and worm wheel mechanism, typically at a 40:1 gear ratio, enabling precise rotational control for simple and compound indexing operations. This design lacks a swiveling base, restricting its use to non-helical applications and focusing on basic circular divisions without angular adjustments. The index plate and crank handle allow for direct selection of divisions, supporting even spacing through sector arms and locking mechanisms to secure positions during machining. These heads are commonly employed in high-volume production scenarios requiring even divisions, such as bolt hole circles on flanges or milling basic spur gears where repetitive, straightforward indexing suffices. Their mechanical simplicity facilitates rapid setup for tasks like cutting hexagonal bolt heads or uniform slots, prioritizing efficiency in batch operations over complex geometries. The advantages of plain indexing heads stem from their streamlined construction, which eliminates tilting components found in more versatile models, resulting in lower manufacturing and acquisition costs while providing enhanced rigidity suitable for heavy cuts on robust workpieces. This rigidity minimizes deflection under load, improving accuracy for production runs, though it limits versatility compared to heads with swivel capabilities for angular work. Early examples include Milling Machines' plain indexing heads, available in 12-inch and 16-inch swings, capable of indexing divisions of 3, 5, and even numbers from 4 to 50, often paired with raising blocks for elevated setups in mid-20th-century shops.

Universal Indexing Heads

Universal indexing heads incorporate a swiveling that enables tilting of the workpiece for angular and helical operations. The typically adjusts from 0° to 90° relative to the horizontal, with many models offering an extended range of -10° to +90° to accommodate undercuts and overhead positions. A dedicated , often with a 40:1 worm-to-spindle ratio, facilitates differential indexing for non-standard divisions and spiral generation by linking the head's input to the machine's lead screw. These devices support all conventional indexing techniques, including , simple, compound, and differential methods, allowing precise rotational positioning of the workpiece. Helical milling is achieved by coordinating the table's longitudinal feed with rotations of the index crank, where the or lead attachment synchronizes spindle turns with table advancement to produce uniform helical paths. The tilting capability provides significant versatility over non-tilting plain indexing heads, enabling the fabrication of intricate features like twisted flutes and bevel gears in a single setup. This design reduces alignment errors and enhances efficiency for work requiring both rotational and angular precision. Early examples include & Sharpe's universal dividing heads, developed in the late 19th and early 20th centuries as components of their universal milling machines, which featured curved seating for the index plate and a 40-tooth sector plate; these models continue to serve in precision shops for their and fine graduations.

CNC and Modern Variants

CNC indexing heads represent an evolution in precision machining, replacing traditional manual cranks with servo motors that enable electronic control and high-speed operation. These devices incorporate digital encoders, often absolute or incremental types such as Hiperface, to provide feedback for exact rotational positioning, achieving resolutions down to 0.001 degrees. Programmability occurs through keypads on standalone units or direct integration with CNC controllers, allowing users to input sequences for automated indexing without mechanical sector plates. The capabilities of CNC indexing heads extend to automated sequencing for complex contours, such as helical or multi-faceted polygons, by eliminating backlash through closed-loop servo systems that dynamically adjust for any positional errors. Integration with CAD/CAM software facilitates the import of rotational paths directly into machine programs, streamlining workflows for production environments. This supports high-volume runs while maintaining consistency across operations. Key advantages include enhanced production speed and exceptional repeatability of ±0.001 degrees, critical for and automotive components requiring tight tolerances. Hybrid models blend CNC precision with manual overrides, allowing operators to switch modes for setup or low-volume tasks, thus combining versatility with . These features minimize downtime and improve overall efficiency in modern shops.

Setup and Operation

Mounting and Alignment Procedures

Mounting an indexing head to a milling machine begins with preparing the worktable and the head's base. The table surface and the base of the must be thoroughly cleaned and stoned to ensure flat contact and prevent inaccuracies. Alignment keys or tongues on the base are inserted into the table's T-slots to initially position the parallel to the machine's X-axis, promoting alignment with the spindle axis. The is then secured using T-slot bolts, clamps, or studs passed through the base's mounting holes into the table's T-slots, tightened evenly to avoid distortion. For the tailstock, it is positioned adjacent to the , aligned by sliding it along the T-slots before clamping with similar hardware. Parallelism between the spindle axis and the tailstock center is verified using a test indicator mounted in the spindle or on the table, sweeping the tailstock center to achieve zero deviation over a 360-degree . Alignment further involves leveling the assembly if the machine table is not perfectly level, using a precision level or dial indicator to check the base relative to the table. Shims may be inserted under the base edges to correct any tilt, ensuring the spindle axis remains parallel to the machine's Y-axis within 0.001 inches. The workpiece is centered between the and tailstock centers by adjusting the tailstock with a until a test indicator shows less than 0.001 inches when rotated. Safety checks are essential prior to operation. Locking mechanisms on the spindle and index crank must be engaged to prevent unintended , and gear in the worm system should be confirmed by attempting manual , which should meet resistance. Adequate clearance between the cutter, workpiece, and components is verified by manual traversal of the table and . Common errors include misalignment of the tailstock, leading to taper in the workpiece or binding during ; these are corrected by repacking the tailstock base with shims and re-indicating for alignment.

Indexing Calculations and Techniques

Simple indexing, the most basic technique for dividing a workpiece into equal parts using an indexing head, relies on the standard 40:1 worm-to-spindle gear ratio common in many models. The number of crank turns required per division is calculated as 40N\frac{40}{N}, where NN is the number of desired divisions around the full 360-degree circle. This value is typically expressed as a mixed number: an number of full crank turns plus a fractional turn, with the fraction determined by selecting an appropriate hole circle on the indexing plate that closely approximates the required movement. For instance, to create 7 equal divisions, the calculation yields 407≈5.714\frac{40}{7} \approx 5.714 crank turns, or precisely 5575 \frac{5}{7} turns. Using a standard indexing plate with a 49-hole circle (common in Brown & Sharpe-style setups), the fractional 57\frac{5}{7} turn corresponds to moving the index pin 35 holes, since 57×49=35\frac{5}{7} \times 49 = 35. The sector arms are adjusted to span 35 holes, ensuring precise repetition for each of the 7 positions. This method works well for divisions where NN is a factor that aligns with available plate hole counts, such as 15, 18, 21, or 49 holes per circle. Compound indexing extends simple indexing for divisions requiring finer or non-standard fractions that cannot be achieved with a single plate circle, by employing an auxiliary shaft geared between two indexing plates (often labeled A and B plates). The crank is disengaged from the main worm, and motion is transmitted through change gears connecting the plates, allowing the effective indexing step to be a product of the two fractions. For example, to achieve complex divisions like those in multi-start threads or irregular polygons, an A-plate with an 18-hole circle might be paired with a B-plate using a 21-hole circle, geared at a 1:1 ratio initially, then adjusted for the specific step (e.g., moving 1 hole on the A-plate while advancing 1 hole on the B-plate per cycle, compounded over multiple turns). This technique multiplies the resolution, enabling up to hundreds of divisions with standard plates. Differential indexing is used for highly precise divisions where simple or compound methods fall short, particularly for large NN values like gear teeth counts not matching plate holes. It involves gearing the index plate directly to the spindle via change gears, creating a continuous adjustment to the indexing motion. The gear ratio RR is calculated as R=40(M−N)MR = \frac{40 (M - N)}{M}, where NN is the desired divisions, MM is the nearest whole number of divisions achievable by simple indexing (approximate value), and 40 is the worm wheel teeth count. For example, to index 51 divisions, select M=50M = 50; then R=40(50−51)50=−45R = \frac{40 (50 - 51)}{50} = -\frac{4}{5}. This ratio is realized with a (e.g., driver 32 teeth to driven 40 teeth, with idlers for direction), allowing the plate to "creep" relative to the spindle for exact spacing. In practice, executing any indexing technique follows a consistent sequence: first, select the appropriate indexing plate and hole circle based on the calculated turns and ; adjust the sector arms to mark the exact movement (e.g., spanning the required holes); engage the index pin in the starting hole and rotate the crank the specified turns plus holes; lock the spindle securely; perform the machining operation; then disengage, advance to the next position, and repeat until all divisions are complete, verifying the full circle closes accurately. This ensures uniform spacing without cumulative error.

Applications

Gear and Flute Cutting

Indexing heads are essential for gear cutting on milling machines, where they enable precise division of the workpiece circumference to form evenly spaced teeth. The gear blank is typically mounted between the centers of the indexing head spindle and a footstock for support, ensuring stability during . A form cutter, such as an cutter selected based on the diametral pitch and number of teeth, is installed in the milling spindle. For a with N teeth, the indexing requires turning the crank 40/N times per tooth space, assuming a standard 40:1 worm gear in the indexing head. For example, cutting a 20-tooth gear involves 40/20 = 2 full crank turns per index to advance the blank by 18 degrees per tooth. The cutting process begins with aligning the blank and cutter, then feeding the cutter into the blank to mill the first tooth space to the required depth, often using climb milling for smoother finishes on materials. After each cut, the cutter is retracted, the indexing head is advanced to the next position, and the cycle repeats for all teeth. To avoid backlash errors, the crank is always rotated in the same direction, and the sector arms on the index plate guide the precise movement. This method achieves typical accuracies of 0.005 inches per tooth space, suitable for many industrial applications. For custom gear profiles, a single-point tool can be used instead of form cutters, allowing greater flexibility in tooth shape. Flute cutting for tools like or reamers follows a similar indexing approach to create straight or helical grooves for chip evacuation and cutting edges. The blank is secured between centers, and equal angular divisions are made based on the number of flutes; for a 4-flute end mill, each index is 90 degrees, requiring 40/4 = 10 full crank turns. A peripheral or is fed axially along the blank while the indexing head rotates it incrementally. For helical flutes, the milling table is geared or manually fed in coordination with the indexing head rotation to produce the spiral path, though detailed helical techniques are covered elsewhere. This process ensures uniform flute spacing and depth, maintaining tool balance and performance.

Polygonal and Helical Machining

The indexing head enables the precise creation of multi-sided polygonal shapes, such as hexagons and octagons, through simple indexing methods that divide the workpiece circumference into equal angular increments. For instance, milling a hexagon on a cylindrical workpiece involves mounting the part between the headstock and tailstock centers, then using straddle milling with two side cutters spaced to the desired flat width; the indexing crank is turned 6 2/3 times (calculated as 40 divisions per turn of the worm wheel divided by 6 sides) to position each face accurately before feeding the workpiece into the cutters. This sequential approach ensures uniform flats without the need for complex setups, commonly applied in producing nuts, bolts, or shaft ends requiring regular polygonal profiles. Helical machining leverages the universal indexing head's ability to tilt the spindle and synchronize with longitudinal table feed, generating spiral paths on the workpiece. The setup connects the table's lead screw to the head via a , allowing controlled advancement per ; the is determined by the relationship, where tan⁡θ=feed per revolutionworkpiece circumference\tan \theta = \frac{\text{feed per revolution}}{\text{workpiece circumference}}, ensuring the cutter traces a true as the part rotates and advances simultaneously. This technique is essential for producing helical grooves, such as those in twist drills or reamers, where the universal head's tilt adjusts for the desired lead angle, and power feed maintains consistent to avoid irregular spirals. Beyond basic polygons and helices, the indexing head supports versatile applications like bolt hole circles on flanges, where simple or differential indexing spaces evenly around a , often using sector arms for rapid positioning. It also facilitates milling curved slots in cams by combining angular indexing with partial rotations to approximate non-circular profiles, converting rotary motion into precise irregular paths. On drill presses, the head attaches to the table for angular hole , tilting the workpiece to exact orientations for features like tapered pins or compound angles in assemblies. These operations achieve tolerances down to 0.001 inches in positioning, supporting high-precision components in demanding fields.

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  18. https://rdl.train.army.mil/catalog-ws/view/100.ATSC/6784A124-F6A8-4CFB-A6D2-1959DE88CCC5-1274445112896/tc_9-524.pdf
  19. https://www.msdiscounttool.com/catalog/content/images/indexing_fixtures.pdf
  20. https://www.petengg.ac.in/department/MECH/notes/Regulation%202021/Sem%2004/MANUFACTURING%20TECHNOLOGY/MT%20NOTES%20UNIT%203.pdf
  21. https://deewanbittal.files.wordpress.com/2017/12/manufacturing-engineering-ii1.pdf
  22. https://www.howengineeringworks.com/questions/what-is-indexing-in-milling-and-how-is-it-performed/
  23. https://www.scribd.com/presentation/358976875/Indexing-in-Milling
  24. https://www.lathes.co.uk/cincinnati/page8.html
  25. https://www.travers.com/product/phase-ii-225-006-indexing-spacer-65-800-001
  26. https://www.knuth.com/en-us/universal-indexing-head-ut-110980
  27. https://www.alibaba.com/product-detail/Universal-indexing-head-F11-200A-with_1601016000669.html
  28. http://vintagemachinery.org/pubs/2098/6525.pdf
  29. https://motionindexdrives.com/product/servo-rotary-index-table/
  30. https://www.kencnc.com/product/view/2
  31. https://www.silvercnc.com/rotary-table/
  32. https://www.okuma.com/files/documents/MA-H2_series-E-8a-300Feb2019.pdf
  33. https://www.eumach.com/umc-1000
  34. https://www.gsaplus.com.tw/e/products_1_4.html
  35. https://uhv.cheme.cmu.edu/procedures/machining/ch8.pdf
  36. https://www.practicalmachinist.com/forum/threads/dividing-head-math-help.220761/
  37. https://www.practicalmachinist.com/forum/threads/dividing-head-plates.76143/
  38. https://www.easymetalworking.mahtg.com/differential-indexing-using-the-dividing-head/
  39. https://www.machinetoolhelp.com/Learn/armymachinetool/ch8.pdf
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