Machining Process Cheatsheet

Cheatsheet Content

### Machine Tools A machine tool is used for **shaping or machining** metal or other rigid materials by cutting, boring, grinding, shearing, or other forms of deformation. They employ a **tool** that performs the cutting or shaping. **Examples of Machine Tools:** - Broaching machine - Drill press - Gear shaper - Hobbing machine - Hone - Lathe - Screw machines - Milling machine - Shear (sheet metal) - Shaper - Saws - Planer - Stewart platform mills - Grinding machines - Multitasking machines (MTMs): CNC machine tools with multiple axes that combine turning, milling, grinding, and material handling. ### Lathe Machine A lathe is a machine tool that **rotates the workpiece on its axis** to perform various operations such as cutting, sanding, knurling, drilling, deformation, facing, or turning. Tools are applied to the workpiece to create an object with symmetry about an axis of rotation. Lathes are used to **remove metal** from the workpiece to achieve a required shape and size. #### Parts of a Lathe - **Bed:** Supports all major components. - **Carriage:** Slides along the ways and consists of the cross-slide, tool post, and apron. Used for longitudinal feed. - **Headstock:** Holds the jaws for the workpiece, supplies power to the jaws, and has various drive speeds. - **Tailstock:** Supports the other end of the workpiece. - **Feed Rod and Lead Screw:** The feed rod is powered by gears from the headstock and is used for turning operations. The lead screw transmits power from the headstock to the carriage for screw thread cutting operations. Unless engaged, there will be no automatic feed. - **Stand (or legs):** Holds the lathe and elevates the bed to a working height. - **Spindle:** A hollow horizontal axle with interior and exterior threads for mounting workpieces. - **Cross-slide:** A flat piece that sits crosswise on the bed, cranked at right angles for cross feed. - **Tool Post:** Sits on top of the cross-slide and holds the cutting tool. - **Tool Rest:** A horizontal area in line with the spindle and tailstock, used to brace hand tools. #### Lathe Accessories Divided into two categories: 1. **Work-holding, -supporting, and -driving devices:** * Lathe centers, chucks, faceplates * Mandrels, steady and follower rests * Lathe dogs, drive plates **1.1 Lathe Centers:** * Work turned between centers must have a center hole drilled in each end. * Support during cutting. * Most common are solid Morse taper shank 60º centers, steel with carbide tips. * Require occasional adjustment and lubrication. **Types of Centres:** * **Live Centre (Revolving Centre):** Constructed so the 60° center runs in its own bearings. Fits in the headstock spindle and rotates with it. * **Dead Centre:** Fits in the tailstock spindle and remains stationary while the work rotates. * **Difference:** A live center revolves with the work in the headstock spindle, while a dead center remains stationary in the tailstock spindle. **1.2 Chucks:** A lathe chuck is mounted on the headstock and holds a rotating workpiece. * **Three-jaw Universal Chuck:** * Holds round and hexagonal work. * Grasps work quickly and accurately. * Three jaws move simultaneously when adjusted by a chuck key. * **Four-Jaw Independent Chuck:** * Used to hold round, square, hexagonal, and irregularly shaped workpieces. * Has four jaws, each adjustable independently by a chuck key. * Jaws can be reversed to hold work by inside diameter. **Difference between Universal Chuck and Independent Chuck:** | Feature | Universal Chuck | Independent Chuck | |-----------------|-----------------------------|-----------------------------| | Workpiece Setup | Easy | Difficult | | Gripping Power | Less | More | | Depth of Cut | Comparatively less | Comparatively more | | Heavy Jobs | Cannot be turned | Can be turned | **1.3 Steady Rest / Fixed Steady:** * Used to support long work held in a chuck or between lathe centers. * Located on and aligned by the ways of the lathe. * Positioned at any point along the lathe bed. * Three jaws tipped with plastic, bronze, or rollers adjust to support any work diameter. **1.4 Travelling Steady/Follower Rest:** * Mounted on the saddle. * Travels with the carriage to prevent work from springing up and away from the cutting tool. * Cutting tool generally positioned just ahead of the follower rest. * Provides a smooth bearing surface for two jaws. **Differences between Steady Rest and Follower Rest:** * Both hold long workpieces steady during turning. * Steady rest is mounted to the lathe bed and does not move with the lathe. * Follower rest is fastened to the carriage and moves with the cutting tool. **1.5 Faceplates:** * Used for holding workpieces that cannot be conveniently held in a chuck. **1.6 Lathe Dog or Carrier:** * Rotates work placed on a mandrel or held between centers by clamping the dog or carrier to the end of the work. * Engaged with a pin attached to the drive plate or face plate. **1.7 Mandrels:** * Cylindrical bars with a center hole at each end. * Used to hold hollow workpieces for machining external surfaces. * The work revolves with mandrels mounted between the lathe centers. 2. **Cutting-tool-holding devices:** * Straight and offset toolholders * Threading toolholders, boring bars * Turret-type tool posts #### Working Principle of Lathe * Holds work between two supports (centers) or using a chuck/faceplate. * Chuck or faceplate is mounted on the machine spindle. * Cutting tool is held and supported on a tool post. * Movement of the job is rotation about the spindle axis. * Tool is fed against the revolving work. * Movement of the tool is either parallel to or at an inclination to the work axis. * If the tool moves parallel, a cylindrical surface is formed. * If the tool moves inclined, a taper surface is produced (taper turning). #### Lathe Operations * **Turning:** Produces straight, conical, curved, or grooved workpieces. * **Facing:** Produces a flat surface at the end of the part or makes face grooves. * **Boring:** Enlarges a hole or cylindrical cavity made by a previous process, or produces circular internal grooves. * **Drilling:** Produces a hole by fixing a drill in the tailstock. * **Threading:** Produces external or internal threads. * **Knurling:** Produces a regularly shaped roughness on cylindrical surfaces. * **Chamfering:** An essential operation after thread cutting. #### Classification of Lathe The following classification covers most lathes used today: 1. **Speed Lathe:** * Named for its **high headstock spindle speed** (usually 1200 to 3600 rpm). * Simplest form, consisting of a headstock, tailstock, and tool-post. * No gearbox, lead screw, or carriage. * Tools are **hand operated**. * **Cone-pulley** is the only source for spindle speed variation. * Applied in wood turning, metal spinning, and polishing. 2. **Engine Lathe or Centre Lathe:** * Most important and widely used machine tool in the lathe family. * Early machine tools were driven by separate engines or from a central engine with overhead belts and shafts. * **Stepped cone-pulley or geared head** often used for varying spindle speed. * Cutting tools controlled by hand or power, fed in cross and longitudinal directions via **carriage, feed rod, and lead screw**. * Can fit a wide range of attachments. 3. **Turret Lathe:** * Used to perform many operations simultaneously. * **Several tools are set on a revolving turret** to facilitate operations with minimum time wastage. * An indexable square tool post on the cross-slide for turning and parting-off tools. * Turret accommodates six tools for operations like drilling, countersinking, reaming, tapping, etc., brought into position by indexing. * Widely used for repetitive batch production. 4. **Capstan Lathe:** * Similar to turret lathes. * In a capstan lathe, the hexagonal turret is carried on a slide mounted in a saddle bolted to the bed. In a turret lathe, the turret is mounted on a slide directly on the bed. * Best suited for **fast production of small parts** due to light weight and short stroke of the capstan slide. 5. **Tool Room Lathe:** * Modern engine lathe with all necessary accessories for accurate tool room work. * Geared head driven machine with considerable range in spindle speeds and feed. * Best suited for production of small tools, dies, gauges, etc. 6. **Bench Lathe:** * Small lathe mounted on a workbench for small, precision, and light jobs. 7. **Gap Bed Lathe:** * Has a gap in the bed near the headstock to handle jobs with flanges or other protruding parts. 8. **Hollow Spindle Lathes:** * Provided with spindles having large through bores to facilitate turning ends of long tubular workpieces. 9. **Vertical Turret Lathes:** * Vertical orientation, used for turning large components conveniently mounted on the machine table. #### Difference Between Centre Lathe and Capstan Lathe | Feature | Centre Lathe | Capstan Lathe/Turret Lathe | |-------------------|---------------------------|----------------------------| | Operation | Manually operated | Semi-automatic | | Number of Speeds | Less | More | | Operations at Once| One | More than one | | Tailstock | Has tailstock | Turret head instead | | Tools Fitted | One | Six different tools | | Tool Changing | More time | Less time | #### Difference Between Capstan Lathe & Turret Lathe | Feature | Capstan Lathe | Turret Lathe | |-----------------|---------------------------|---------------------------| | Duty | Light duty machine | Heavy duty machine | | Workpiece | Short workpiece | Long workpiece | | Saddle Movement | Not moved during machining| Moved during machining | | Turret Head | Mounted on ram | Directly on saddle | #### Copying Lathe Used to reproduce shapes faithfully and consistently from a template. * **Types:** Mechanical, Hydraulic, and Electric. * **Hydraulic Type:** Servo-motor systems that magnify a small input force to provide a large output force for machine operation. #### Size and Specification of Lathe Size is specified by: 1. Height of centers measured over the lathe bed. 2. Swing or maximum diameter that can be rotated over the bed ways. 3. Swing or diameter over carriage (largest diameter of work revolving over the saddle). 4. Maximum job length (mm) between centers. 5. Bed length (meters). 6. Diameter of the hole through the lathe spindle. Additional specifications for ordering: i. Length, width, and depth of bed. ii. Depth and width of the gap (for gap lathe). iii. Swing over gap. iv. Number and range of spindle speeds. v. Number of feeds. vi. Lead screw diameter. vii. Number and range of metric threads. viii. Tailstock spindle travel. ix. Tailstock spindle set over. x. Back gear ratio. xi. Power rating of electric motor. ### Milling Machine Milling is a machining process using **rotary cutters** to remove material from a workpiece by advancing (feeding) the cutter at an angle to its axis. It covers various operations from small parts to large, heavy-duty gang milling. It's widely used for machining parts to precise sizes and shapes. The milling cutter is a rotary cutting tool with multiple cutting points. Unlike drilling, where the tool advances along its rotation axis, in milling, the cutter is usually moved **perpendicular to its axis** so cutting occurs on its circumference. As the cutter enters, its cutting edges repeatedly cut into and exit the material, shaving off chips (tiny clumps of material). The cutting action is **shear deformation**. #### Specifications of Milling Machine 1. **Size of the work table:** Expressed in length x width (e.g., 1500 x 30mm). 2. **Longitudinal movement (X-direction):** Total movement of table in mm (e.g., 800mm). 3. **Transverse movement (Y-direction):** Total movement of saddle along with table in mm (e.g., 200mm). 4. **Vertical movement (Z-direction):** Total movement of table, saddle & knee in mm (e.g., 380mm). 5. **Range of the speed:** Speed variation in the gearbox in RPM (e.g., 45 to 200 rpm). 6. **Power capacity of the motor:** In HP (e.g., 2 HP). #### Principal Parts * **Base:** Provides rest for all parts, made of grey iron casting. * **Column:** A rigid vertical long box housing the spindle's driving mechanism. The table and knee are fixed to its guideways. * **Knee:** Adjustable in height on the column, houses the **feed mechanism** of the table and other controls. * **Saddle:** Placed on top of the knee, provides **guideways** for table movement. * **Table:** Rests on the saddle, has T-slots for clamping the workpiece. **Feed motions** are controlled by a lead screw. * **Overhanging Arm:** Mounted on the column, serves as a **bearing support for the arbor**. Adjustable to provide support near the milling cutter. * **Arbor:** Holds **rotating milling cutters** rigidly and is mounted on the spindle. A stub arbor is supported at maximum distance like a cantilever. Locking provisions ensure reliability. * **Front Brace:** Adjusts the relative position of the knee and overhanging arm, providing extra support for rigidity. * **Spindle:** Projects from the column face with a tapered hole for the arbor. Its performance depends on accuracy, strength, and rigidity. Transfers motive power to the arbor via belt or gear. #### Types of Milling Machines I. **Knee and Column Type:** a. Horizontal b. Vertical c. Universal d. Turret type II. **Production (Bed) type:** a. Simplex b. Duplex c. Triplex III. **Plano millers** IV. **Special type:** a. Rotary table b. Drum type c. Copy milling d. Key way milling machines e. Spline shaft milling machines #### Universal Milling Machine * Used for a **large variety of operations**. * Distinguishing feature: **table is mounted on a circular swiveling base** with degree graduations. * Table can be **swiveled to any angle** on either side of normal position. * **Helical milling operation** is possible as the table can be fed to the cutter at an angle. * Large number of auxiliaries (dividing head, vertical milling attachments, rotary table) make it versatile. #### Milling Operations 1. **Angular Milling:** For angular cuts like V-notches & grooves (double angle cutter). 2. **Form Milling:** Produces various types of forms (form cutter). 3. **Plain Milling/Slab:** Creates flat surfaces on the workpiece (plain cutter). 4. **Face Milling:** Produces flat surfaces (face milling cutter). 5. **End Milling:** Produces flat surfaces (end milling cutter). 6. **Slot Milling:** Produces slots like T-slot, plain slots etc. 7. **Gang Milling:** Produces many surfaces on a workpiece simultaneously. **Two Major Classes of Milling Process:** * **Face Milling:** * Cutting action primarily at the **end corners** of the milling cutter. * Used to cut flat surfaces (faces) or flat-bottomed cavities. * Cutter axis is **perpendicular** to the surface being machined. * **Peripheral Milling:** * Cutting action primarily along the **circumference** of the cutter. * The cross-section of the milled surface receives the shape of the cutter. * Cutter axis is **parallel** to the surface being machined, and cutting edges are on the outside periphery. #### Indexing The method of dividing the periphery of a job into an equal number of divisions. * Operation of rotating the job through a required angle between successive cuts. * Accomplished using a **dividing head**, an accessory to the milling machine. * Divides the job periphery into equal divisions. * To rotate a job through a required angle, a device to rotate the job and a source to ensure rotation through the desired angle are needed. * In a dividing head, an index-crank rotates the job, and an index plate ensures the correct angle. * The index-plate has concentric circles of equally spaced holes. * Crank rotation is transmitted to the job via a gear. * The ratio of the crank and the shaft on which the job is mounted is **40:1** (40 turns of the index crank for one spindle revolution). **Methods of Indexing:** 1. Direct Indexing 2. Simple Indexing 3. Compound Indexing 4. Differential Indexing 5. Angular Indexing Method #### Index Plate Types * **Brown and Sharpe type:** 3 plates, 6 circles each. * Plate I: 15, 16, 17, 18, 19, 20 holes * Plate 2: 21, 23, 27, 29, 31, 33 holes * Plate 3: 37, 39, 41, 43, 47, 49 holes * **Cincinnati type:** One plate drilled on both sides. * First side: 24, 25, 28, 30, 34, 37, 38, 39, 41, 42, 43 holes * Second side: 46, 47, 49, 51, 53, 54, 57, 58, 59, 62, 66 holes #### Simple Indexing or Plain Indexing * An index plate is selected, fitted on the worm shaft, and locked by a pin. * To index, the crank pin is withdrawn, the crank is turned through a calculated number of revolutions and holes, and the pin is re-located. * Formula: $N = 40 / Z$, where $Z$ is the number of divisions. * Example: For 8 teeth, $40/8 = 5$ turns. For 10 teeth, $40/10 = 4$ turns. * Example: For 16 divisions, $40/16 = 2 \frac{8}{16}$ turns (2 complete rotations + 8 holes on a 16-hole circle). #### Difference Between Horizontal and Vertical Milling Machine | Feature | Horizontal Milling Machine | Vertical Milling Machine | |---------------------|---------------------------------|-------------------------------| | Spindle Orientation | Horizontal to worktable | Vertical to worktable | | Cutter Movement | Cannot move up/down | Can move up/down | | Spindle Tilt | Cannot be tilted | Can be tilted | | Operations | Plain, form, gang milling | Slot, T-slot, angular, flat milling | | Cutter Mounting | Mounted on arbor | Directly on spindle | #### Difference Between Up Milling & Down Milling | Feature | Up Milling (Conventional) | Down Milling (Climb) | |---------------------|---------------------------------|-------------------------------| | Workpiece Feed | Opposite direction of cutter | Same direction of cutter | | Cutting Force | Directed upwards | Directed downwards | | Clamping | Strong clamping required | Strong clamping not required | | Chips | Progressively thicker | Progressively thinner | | Surface Finish | Poor | Good | | Material | Used for hard material | Used for soft material | ### Shaper A shaper is a machine tool that produces **flat surfaces** in horizontal, vertical, or inclined planes, depending on the cutting tool's orientation. #### Features * **Single point cutting tool** is used. * Tool is clamped in the tool post on the ram. * The ram reciprocates, the tool cuts material in the **forward stroke**, and there is no cutting in the return stroke. * Job is held rigidly in a vice. #### Principle of Working * The job is rigidly fixed on the machine table. * The single point cutting tool, held in the tool post, is mounted on a reciprocating ram. * The ram's reciprocating motion is obtained by a **quick return motion mechanism**. * During the forward stroke, the tool cuts. The return stroke is an **idle stroke** with no cutting action. * The forward and return strokes constitute one operating cycle. * Shaping machines use a quick return mechanism (usually crank and slotted-link design) to reduce time wasted during the non-cutting return stroke. #### Quick Return Mechanism * Mechanism that makes the return stroke faster than the cutting stroke. * Converts rotary motion into reciprocating motion. * Reduces idling time. Shaper machine is a primary example. #### Working of Quick Return Mechanism The crank AB (adjustable length R) rotates at a uniform angular speed. The crank pin B (die block) slides freely inside the slot of the slotted lever OBC. Lever OBC is pivoted at O, and its other end C connects to the ram by a short link arm. When crank AB rotates clockwise from AB₁ to AB₂, the ram moves forward. When it rotates from AB₂ to AB₁, the ram returns. The time for the forward stroke is proportional to angle $\alpha$, and the return stroke is proportional to angle $\beta$. The return stroke is completed in less time. #### Why Quick Return Mechanism? * A shaper cuts only on the forward stroke; the backward stroke is idle (wastage). * To minimize this wastage, the return stroke should be completed as quickly as possible. #### Specification of Shaper Machine 1. Maximum length of stroke of Ram 2. Power input 3. Floor Space required 4. Weight of the machine 5. Cutting to Return Stroke ratio range 6. Feed range 7. Adjustable range (depth) #### Difference Between Shaper and Planer Machine | Feature | Shaper Machine | Planer Machine | |---------------------|---------------------------------|-------------------------------| | Cutting Tool | Reciprocates | Stationary | | Workpiece | Stationary | Reciprocates | | Workpiece Size | Suitable for small workpieces | Suitable for larger workpieces| | Tool Size | Smaller | Larger | | Cut | Lighter cut | Heavier cut | | Initial Cost | Less | High | | Space | Occupies smaller work area | Occupies larger work area | ### Other Machining Operations #### Boring Operation Enlarging a hole that has already been drilled or cast, using a single-point cutting tool or a boring head with multiple tools (e.g., in gun barrels or engine cylinders). #### Broaching Operation * Uses a toothed tool called a **broach** to remove material. * **Types:** Linear and rotary. * **Linear broaching:** Broach runs linearly against workpiece. * Broaching is used for **precision machining**, especially for odd shapes (circular/non-circular holes, splines, keyways, flat surfaces). * Typical workpieces: small to medium-sized castings, forgings, screw machine parts, stampings. * Broaches are expensive, but favored for **high-quantity production runs**. * Broaches are shaped like a saw, with teeth height increasing along the tool. * Contains three sections: roughing, semi-finishing, finishing. * The feed is built into the tool; the machined surface's profile is inverse to the broach's. #### Sawing Operation * Uses a **multipoint cutting tool (saw)**. * Multiple teeth move through the workpiece, each deepening the cut. * Feed is given to either the saw or the workpiece. #### Honing Machine * Abrasive machining process that produces a precision surface by scrubbing an abrasive stone along a controlled path. * Primarily improves geometric form; can also improve surface texture. * Applications: finishing cylinders for internal combustion engines, air bearing spindles, gears. * Many types of hones, all with one or more abrasive stones held under pressure. * The hone rotates in the bore while moving in and out. * Special cutting fluids are used for smooth cutting and material removal. #### Hobbing Machine * Machining process for gear cutting, cutting splines, and cutting sprockets. * A special type of milling machine. * Teeth or splines are progressively cut into the workpiece by a series of cuts from a cutting tool called a **hob**. #### Difference Among Drilling, Boring, and Reaming * **Drilling:** Makes cylindrical bores using a drill bit. * **Boring:** Enlarges existing drilled holes using a boring bar. * **Reaming:** Finishes holes or slightly removes material for accuracy using a reamer. #### Difference Among Counter Boring, Counter Sinking & Counter Drilling * **Counter Boring:** Enlarges one end of an existing hole concentrically. * **Counter Sinking:** Enlarges the top portion of an existing hole to a conical shape. * **Counter Drilling:** Drilling in the opposite direction. ### Cutting Tools A cutting tool (or cutter) removes material from a workpiece to achieve the required size and shape. #### Types of Cutting Tools 1. Single Point Cutting Tool 2. Double Point Cutting Tool 3. Multi Point Cutting Tool #### Characteristics of Cutting Tools * Hot hardness * Wear resistance * Toughness * Chemical affinity * Favorable cost * Availability * Low coefficient of friction * Shock resistance #### Difference Between Single Point and Multi Point Cutting Tool | Feature | Single Point Cutting Tool | Multi Point Cutting Tool | |----------------|-------------------------------------|--------------------------------------| | Cutting Edges | One | Two or more | | Shape | Simple | Complex | | Typical Use | Lathe machine | Milling and drilling machines | #### Cutting Tool Material * Diamond * Tool steel * High speed steel * High carbon steel * Ceramics #### Working and Auxiliary Motion * **Auxiliary Motion:** Motion not directly involved in forming the surface but essential for the working motion (e.g., clamping/unclamping workpiece). * **Machining Process Relationship:** Cutting speed and feed rate define the process. * **Cutting speed ($V$):** m/min * **Feed rate ($S$):** mm/rev (lathe, boring, drilling), mm/tooth (milling), mm/stroke (shaping, planning), mm/min (milling). #### Formulas * **For Rotary working motion:** $V = \pi DN/1000$ (where $D$ is diameter in mm, $N$ is rpm). * **For Reciprocating motion:** $V = L/(1000 T_c)$ (where $L$ is length in mm, $T_c$ is time of cutting stroke in min). * **Relation between cutting stroke and cutting speed:** $V = nL(K+1)/1000K$ * Where $K = T_i/T_c$ ($T_i$ = time of idle stroke in min), $n$ = number of strokes per minute = $1/(T_c+T_i) = K/T_c(1+K)$. * **Feed per revolution/stroke and feed per minute:** $S_m = S \cdot n$ (where $S_m$ is feed per minute, $S$ is feed per rev/stroke, $n$ is number of rev/stroke per min). * **Feed per tooth in multiple cutter:** $S = S_z \cdot Z$ (where $S$ is feed per rev/stroke, $Z$ is number of teeth, $S_z$ is feed per tooth). * **Machining time ($T_m$):** $T_m = L/S_m$ (where $L$ is length of machined surface, $S_m$ is feed per minute). #### Mathematical Problems (Examples) 1. **Spindle speed:** Determine for a 12mm diameter high steel drill cutting medium carbon steel at 28 m/min. 2. **Machining time (drilling):** Determine for a 20mm diameter hole, 25mm thick, cutting speed 30 m/min, feed 0.2 mm/rev. 3. **Time required (drilling):** For a 30mm H.S.S. drill in a 100mm thick cast iron block, feed 0.30 mm/rev, over travel 4mm, cutting speed 20 m/min. 4. **Time required (shaper):** For a 600mm x 30mm flat surface, 20mm over-travel at each end, average cutting speed 8m/min, feed rate 0.3mm/stroke, return time to cutting time ratio 1:2. 5. **Optimum tool cost (lathe turning):** For 250mm length, 25mm diameter bars, feed 0.2mm/rev. Regrinding cost Rs. 20, tool change time 1 min. Tool life equation $VT^{0.2}=24$. 6. **Planning time:** For a 2000mm length, 300mm width workpiece, feed 0.3mm/stroke, 10 double strokes/min. 7. **Time required (drilling):** For a 31.8mm HSS drill in a 100mm thick cast iron block, cutting speed 20 m/min, feed 0.3 mm/rev, over travel 4mm, approach 9mm.