Question 1

Turning practice: What is the typical average cutting speed range for turning mild steel using a high-speed steel (HSS) single-point tool?

Accepted Answer

Introduction / Context: Choosing a proper cutting speed in turning is fundamental for tool life, surface finish, and productivity. For mild steel turned with a high-speed steel (HSS) tool, recommended speeds are modest because HSS loses hot hardness at elevated temperatures. This question checks recall of standard shop-floor values and the reasoning behind them. Given Data / Assumptions: Work material: mild steel (low carbon steel). Tool material: HSS single-point tool. Objective: typical average cutting speed range, not the extreme ends. Normal dry or lightly lubricated conditions, conventional lathe. Concept / Approach: Cutting speed must balance reasonable metal removal with acceptable tool life. HSS tools retain hardness up to a lower temperature than carbide or ceramics; therefore, their recommended speeds are lower. Practical shop tables and the Taylor tool life relationship support speeds in the few tens of metres per minute for mild steel with HSS. Step-by-Step Solution: Identify tool material limitations: HSS requires relatively low speeds.Identify work material: mild steel is not abrasive but still generates heat.Use common ranges from handbooks: about 25–30 m/min for general turning with HSS.Select the listed option that brackets this range. Verification / Alternative check: Applying Taylor’s tool life notion qualitatively: raising speed sharply reduces tool life for HSS, confirming that high values such as 60–90 m/min or greater are usually reserved for carbide or coated tools. Why Other Options Are Wrong: 15 to 19 m/min: overly conservative for routine mild steel turning. 60 to 90 m/min and 90 to 120 m/min: typical of carbide or better tool materials, not HSS. Common Pitfalls: Confusing HSS recommendations with carbide; ignoring coolant and rigidity effects can also mislead selection. Final Answer: 25 to 31 m/min

Question 2

Drilling fundamentals: A 20 mm diameter drill runs at 500 r.p.m. with a feed of 0.2 mm/rev to make a through-hole in a 20 mm thick mild-steel plate. What is the depth of cut in this drilling operation?

Accepted Answer

Introduction / Context: In drilling, several quantities are defined differently than in turning. The term “depth of cut” in drilling is a geometric measure defined by convention and does not refer to plate thickness or feed. This question tests correct identification of the drilling depth of cut. Given Data / Assumptions: Drill diameter, D = 20 mm. Rotational speed, N = 500 r.p.m. (not required for depth of cut). Feed, f = 0.2 mm/rev (not required for depth of cut definition). Plate thickness = 20 mm (this is the drilling depth, not the “depth of cut”). Concept / Approach: By standard machining terminology, for drilling: depth of cut (t) = D/2. The rationale is that each cutting lip removes material equivalent to a radial engagement equal to half the drill diameter. The feed per revolution relates to chip thickness per lip, while the plate thickness relates to the axial drilling depth, not the depth of cut. Step-by-Step Solution: Use definition: t = D/2.Substitute D = 20 mm.t = 20 / 2 = 10 mm.Therefore, the depth of cut is 10 mm. Verification / Alternative check: If asked for material removal rate, one would use feed and speed; here, only the geometrical convention for drilling depth of cut is needed. Why Other Options Are Wrong: 0.2 mm: this is the feed per revolution, not depth of cut. 20 mm: this is the plate thickness (axial depth), not the drilling depth of cut. 100 mm: unrelated numerical distractor. Common Pitfalls: Confusing axial drilling depth with depth of cut; mixing feed with depth of cut definition. Final Answer: 10 mm

Question 3

Lathe spindle standard: The built-in spindle taper commonly provided in engine lathes is approximately

Accepted Answer

Introduction / Context: Lathe spindles incorporate a self-holding taper to accept centres, drive plates, and tool holding attachments. Recognizing the typical taper ratio helps with accurate setup and compatibility across standard tooling. Given Data / Assumptions: Conventional engine lathe, internal spindle nose taper is of the self-holding type. Approximate ratio is sought (on diameter basis). Focus is on typical practice rather than a specific manufacturer variant. Concept / Approach: Self-holding tapers like Morse tapers are widely used. Their included angles and taper ratios are such that they wedge securely under light load but can be released when needed. A commonly remembered approximate taper magnitude is close to 1 in 20 on diameter for these applications, aligning with many shop exam conventions. Step-by-Step Solution: Recall the standard self-holding taper used in lathe spindles.Associate the typical taper magnitude used in exam and shop references.Select 1 in 20 as the commonly accepted approximate ratio.Hence, the correct option is 1 in 20. Verification / Alternative check: Handbooks list exact Morse taper data varying by size; the approximate value aligns best with 1 in 20 among the options provided. Why Other Options Are Wrong: Ratios such as 1 in 10 or 1 in 30 do not match the widely cited approximate spindle self-holding taper for general engine lathes. Common Pitfalls: Confusing different taper systems (self-releasing vs self-holding) or mixing angle vs ratio on radius vs diameter. Final Answer: 1 in 20

Question 4

Tool life dependence: According to practical machining experience and Taylor’s equation, tool life is __________ cutting speed.

Accepted Answer

Introduction / Context: Tool life is a primary economic and quality metric in machining. The classic Taylor tool life equation formalizes how tool life varies with cutting speed and other factors. Understanding this dependency guides reliable process planning. Given Data / Assumptions: Conventional turning or similar cutting process. Other variables (feed, depth, tool and work materials) are held comparable. We refer to the qualitative dependence, not exact exponents. Concept / Approach: Taylor’s tool life equation is commonly stated as V * T^n = C, where V is cutting speed, T is tool life, n is an exponent depending on tool/work pair, and C is a constant. This shows an inverse relationship between speed and life: as speed increases, tool life decreases rapidly. Step-by-Step Solution: Recognize the governing empirical relationship V * T^n = C.For constant C and n, higher V forces T to reduce.Therefore, tool life clearly depends on cutting speed.Select the option reflecting dependence. Verification / Alternative check: Shop data consistently show accelerated flank wear and crater wear at higher speeds for the same feed and depth, confirming dependence. Why Other Options Are Wrong: “Independent of” contradicts extensive empirical and theoretical evidence. Common Pitfalls: Assuming only speed matters; in reality, feed, depth, tool grade, and coolant also influence T, but speed is the dominant factor in most cases. Final Answer: dependant upon

Question 5

Grinding abrasives: Aluminium oxide (Al2O3) wheels are chiefly recommended for grinding which of the following materials?

Accepted Answer

Introduction / Context: Selecting the proper abrasive is critical for grinding efficiency and surface integrity. Aluminium oxide is the most widely used abrasive for ferrous materials because it fractures in a controlled way and resists chemical reaction with iron at grinding temperatures. Given Data / Assumptions: Abrasive: aluminium oxide (Al2O3). Target materials: high speed steel, carbon steel, and wrought iron. General-purpose surface or cylindrical grinding conditions. Concept / Approach: Aluminium oxide is preferred for steels and wrought iron. Silicon carbide, in contrast, is harder but more brittle and is preferred for non-ferrous metals, hard carbides, and cast iron of certain grades. Therefore, for the list of ferrous materials provided, aluminium oxide is suitable for all. Step-by-Step Solution: Identify the work materials: all are ferrous and ductile relative to abrasives.Match abrasive to material: Al2O3 for steel and wrought iron.Conclude that all listed materials suit Al2O3 wheels.Select “All of these”. Verification / Alternative check: Manufacturer catalogs recommend Al2O3 for tool steels (including HSS), plain carbon steels, and wrought iron products. Why Other Options Are Wrong: Limiting the choice to any single listed material understates the broad applicability of aluminium oxide to ferrous metals. Common Pitfalls: Confusing aluminium oxide with silicon carbide applications; mixing up the role of grit size with abrasive type. Final Answer: All of these

Question 6

Heat generation in machining: The region where maximum heat is produced due to plastic deformation of the work material is called the

Accepted Answer

Introduction / Context: Understanding where heat is generated in cutting helps in selecting cutting parameters, tool materials, and coolants. Heat affects tool wear, surface integrity, and dimensional accuracy. Given Data / Assumptions: Orthogonal cutting model for clarity. Three regions of interest: primary shear zone, secondary deformation (friction) zone on rake face, and tertiary zone at tool flank. We seek the region of maximum heat generation from plastic deformation. Concept / Approach: The primary shear zone (often called the shear zone) is where the chip forms as layers of metal undergo severe plastic shear. Most plastic work—and thus the bulk of heat from deformation—occurs here. The friction zone also generates heat, but it is due to sliding at the tool–chip interface, not primarily plastic deformation. Step-by-Step Solution: Identify heat sources: primary shear work and frictional work.Attribute plastic deformation heat to the primary shear zone.Conclude that the region of maximum plastic-deformation heat is the shear zone.Select the option “shear zone”. Verification / Alternative check: Energy partition studies show a dominant share of mechanical work converting to heat in the shear zone for typical cutting conditions. Why Other Options Are Wrong: Friction zone is a major heat source but arises from sliding, not primarily plastic deformation; “work–tool contact zone” is a broad phrase and does not isolate the primary shear region. Common Pitfalls: Assuming all heat is from friction; in many metals and conditions, primary shear work dominates. Final Answer: shear zone

Question 7

Shaper kinematics: In a standard shaper, which element reciprocates during cutting while the other stays stationary?

Accepted Answer

Introduction / Context: A shaper is used to produce flat surfaces by a single-point tool attached to a ram. Knowing the basic motion scheme is essential to understand stroke settings, feeds, and productivity. Given Data / Assumptions: Conventional horizontal shaper with a ram and tool head. Work is clamped on the table or vice. Feed is provided by incremental table movement between strokes. Concept / Approach: The shaper operates with a reciprocating ram carrying the tool. The cutting happens primarily on the forward stroke (quick-return mechanisms shorten the return). The work remains stationary during each stroke, except for a small indexing feed after each cycle. Step-by-Step Solution: Identify the moving component that executes the stroke: the ram with tool.Recognize that the work is clamped and does not reciprocate.Hence, the correct description is: work stationary, tool reciprocates.Select the appropriate option. Verification / Alternative check: Observation of any standard shaper confirms the reciprocating tool motion and fixed work during strokes. Why Other Options Are Wrong: They contradict the basic design of the shaper where the tool, not the work, performs the reciprocating motion. Common Pitfalls: Confusing a shaper with a planer; in planers, the worktable reciprocates while the tool is stationary except for feed. Final Answer: Work is stationary and tool reciprocates

Question 8

Hole finishing: The operation that produces a cone-shaped enlargement at the mouth of a drilled hole is called

Accepted Answer

Introduction / Context: After drilling, holes are often modified to seat fasteners or improve fit. Recognizing the correct secondary operation is important for proper assembly and surface quality. Given Data / Assumptions: A drilled hole requires a conical mouth to seat a flat-head screw or remove burrs. Standard shop operations are considered. Concept / Approach: Counter-sinking cuts a cone at the hole entrance, typically matching screw head angles. Counter-boring creates a cylindrical recess for socket heads; spot facing produces a flat, smooth seating surface around a hole; trepanning removes a circular disk rather than producing a conventional hole. Step-by-Step Solution: Identify the desired geometry: conical recess at the hole entrance.Match operation to geometry: counter-sinking produces a cone.Therefore, select counter-sinking.Reject alternatives that produce cylindrical or flat seats. Verification / Alternative check: A countersink tool has a conical cutting form (commonly 60°, 82°, 90°, or 120° included angle) corresponding to standard screw heads. Why Other Options Are Wrong: Counter-boring: cylindrical recess, not conical. Trepanning: core removal method. Spot facing: flat circular seat, not a cone. Common Pitfalls: Confusing counter-sinking with counter-boring; always visualize the required seat shape. Final Answer: counter-sinking

Question 9

Grinding methods: Which grinding process is used primarily to finish internal cylindrical holes and internal tapers?

Accepted Answer

Introduction / Context: Grinding processes are chosen based on the surface to be generated. Internal features require specialized wheel shapes, spindles, and setups to achieve accuracy and surface finish inside bores and tapers. Given Data / Assumptions: Feature to be finished: internal cylindrical holes and internal tapers. Conventional precision grinding equipment is available. Concept / Approach: Internal cylindrical grinding uses a small grinding wheel mounted on a high-speed spindle inserted into the bore. The work typically rotates on a chuck or between centres while the wheel feeds and traverses to generate the required geometry and finish. This differs from external cylindrical grinding, which treats the outside diameter, and surface grinding, which treats planar surfaces. Step-by-Step Solution: Match the required surface (internal bore/taper) to the process.Identify “internal cylindrical grinding” as the process designed for bores and internal tapers.Eliminate processes aimed at external or planar features.Select internal cylindrical grinding. Verification / Alternative check: Inspection of typical machine configurations confirms that internal grinders accommodate small wheels and precise bore gauging. Why Other Options Are Wrong: Form grinding is for complex profiles; external cylindrical grinding is for outside diameters; surface grinding is for flat faces. Common Pitfalls: Attempting to use external grinding on internal geometries or misidentifying honing/lapping as grinding; those are distinct finishing processes. Final Answer: Internal cylindrical grinding

Question 10

Turning tapers: For producing a small taper over a long workpiece on the lathe, which method is generally the most suitable?

Accepted Answer

Introduction / Context: Several methods exist to turn tapers on a lathe. Selecting the right method depends on the taper angle magnitude and the length of the taper required. This question targets the common scenario of a small (shallow) taper over a relatively long workpiece. Given Data / Assumptions: Taper is small (shallow angle). Taper length is long relative to workpiece diameter. General purpose engine lathe with standard accessories. Concept / Approach: Setting over the tailstock offsets the axis of rotation slightly, producing a gradual taper along the full length between centres. It is ideal for long, shallow tapers. Swivelling the compound rest is better for short, steeper tapers. A taper turning attachment is flexible and accurate for various angles but is often used when higher precision or repeatability is needed. A form tool is only suitable for short tapers due to deflection and tool geometry limits. Step-by-Step Solution: Identify the taper requirements: long length and small angle.Match method: tailstock set-over yields long shallow taper between centres.Eliminate methods more appropriate for short or steep tapers.Choose “Setting over the tailstock”. Verification / Alternative check: Workshop practice confirms tailstock offset is conventional for long gentle tapers with minimal setup complexity. Why Other Options Are Wrong: Form tool: poor for long tapers, high cutting load. Taper attachment: good but not necessary for small angles over long lengths. Compound rest: limited travel, best for short tapers. Common Pitfalls: Overusing the compound rest for long tapers, leading to feed travel limitations and non-uniform finish. Final Answer: Setting over the tailstock

Question 11

Understanding shear velocity in metal cutting In orthogonal/oblique machining, “shear velocity” refers to the velocity of material flow along the shear plane within the work material (relative to the work), not along the tool face or relative to the…

Accepted Answer

Introduction / Context: In metal cutting theory (Merchant analysis), three fundamental velocities are used: cutting velocity, chip (sliding) velocity, and shear velocity. Students often confuse these with one another because they occur simultaneously at different interfaces of the cutting zone. Given Data / Assumptions: Conventional turning or orthogonal cutting is considered. The tool is sharp and the chip forms by primary shear along a well-defined shear plane. Steady-state cutting (constant speed, feed, and depth of cut). Concept / Approach: Cutting velocity V is the velocity of the work surface past the tool (work relative to tool). Chip (or sliding) velocity Vc is the velocity of chip flow up the rake face (chip relative to tool). Shear velocity Vs is the material flow velocity along the shear plane, i.e., inside the work material across the primary deformation zone, typically taken relative to the work. Step-by-Step Solution: Identify what is being asked: the definition of shear velocity.Recall the velocity triangle: V is the vector sum of Vs and Vc (V = Vs + Vc). Each vector represents a different interface.Observe that “chip relative to tool” corresponds to Vc, not Vs; “tool relative to work” corresponds to V, not Vs.Therefore, none of the listed options directly states “velocity along the shear plane in the work material,” so “None of these” is correct. Verification / Alternative check: Standard machining texts depict the velocity triangle and label Vs along the shear plane, distinct from V (work-tool) and Vc (chip-tool) directions. Why Other Options Are Wrong: Tool relative to the workpiece: that is the cutting velocity V, not Vs.Chip relative to the tool: that is chip/sliding velocity Vc, not Vs.Tool motion along the tool face: describes Vc direction, not Vs. Common Pitfalls: Assuming the largest velocity must be the shear velocity or equating chip sliding with shearing. Always relate each velocity to its physical interface. Final Answer: None of these

Question 12

Recommended drill point angle for bakelite and fibrous plastics In practical drilling of brittle thermosets (e.g., bakelite) and fibrous plastics, which point angle is commonly used to reduce cracking and delamination while ensuring a clean entry?

Accepted Answer

Introduction / Context: Bakelite (a thermoset phenolic) and many fiber-reinforced plastics are prone to edge chipping and delamination during drilling. Choosing a suitable point angle helps control thrust and cutting action to protect the material. Given Data / Assumptions: Brittle or fibrous non-metallic workpiece. Standard twist drill geometry is being considered (no special brad-point, step, or core drills). Conventional manual or machine drilling with appropriate fixturing. Concept / Approach: A smaller point angle (sharper point) like about 90° produces a keener cutting action and reduces the pushing (extrusion-like) effect that promotes cracking. Typical “general-purpose” 118° or 135° points suit metals but can induce higher thrust in brittle plastics. For bakelite and laminates, 90° and specialized geometries (e.g., spade or brad points) are commonly recommended. Step-by-Step Solution: Identify the material behavior: brittle or layered → sensitive to high thrust and heat.Select a point angle that minimizes thrust at the chisel edge → approximately 90°.Confirm that this geometry improves entry quality and reduces delamination risk. Verification / Alternative check: Shop handbooks and plastics drilling guidelines list 90° as a go-to for brittle plastics, often with reduced feed and higher spindle speeds plus backing support. Why Other Options Are Wrong: 118° and 135°: common for steels; tend to increase thrust on plastics.150°: excessively blunt for these materials; likely to crack the surface.60°: too acute; weak chisel region and potential wandering. Common Pitfalls: Neglecting backup boards under thin laminates; not clearing chips (melting/smearing); using feeds/speeds meant for metals. Final Answer: 90°

Question 13

Velocity triangle insight In orthogonal cutting, consider the standard velocity triangle that relates cutting velocity (V), chip velocity along the tool face (Vc), and shear velocity along the shear plane (Vs). The vector sum of cutting velocity and…

Accepted Answer

Introduction / Context: Understanding the velocity triangle helps in analyzing chip flow and energy partitions in machining. Each velocity corresponds to a distinct physical interface: work-tool, chip-tool, and shear plane within the work material. Given Data / Assumptions: Orthogonal cutting with a defined rake angle. Steady state cutting and continuous chip formation. Conventional sign and vector directions (Merchant diagram). Concept / Approach: The well-known vector relationship is V = Vs + Vc (vector sum). That is, the cutting velocity equals the vector sum of shear and chip velocities, not vice versa. Consequently, if one were to sum V and Vc, the resulting vector would not equal Vs and will generally have a larger magnitude than Vs due to triangle inequality. Step-by-Step Solution: Recall the velocity triangle: V is the vector sum of Vs and Vc.Rearrange: Vs = V − Vc (vector), not V + Vc.Therefore, the vector sum (V + Vc) must have a magnitude greater than Vs (in general), so the correct relational word is “more than.” Verification / Alternative check: Draw a representative triangle for a positive rake angle; measure magnitudes to see |V + Vc| > |Vs| typically holds. Why Other Options Are Wrong: Equal to: incorrect by the fundamental relation (V = Vs + Vc).Less than: contradicts the triangle inequality for typical geometries.Undefined without rake angle: directions depend on geometry, but the algebraic relation and inequality stand in general.Opposite to: incorrect; the vectors are not opposite by definition. Common Pitfalls: Confusing which pair sums to which; always anchor the triangle on the physical interfaces to avoid sign/direction errors. Final Answer: more than

Question 14

Standard included angle of lathe centres In general-purpose engine lathes, what is the standard included angle used for live and dead centres that support workpieces between centres?

Accepted Answer

Introduction / Context: Turning between centres requires accurately ground centres on both the work and the lathe. The included angle of these centres must be standardized for compatibility and load-carrying capability. Given Data / Assumptions: Conventional engine lathe with Morse taper live/dead centres. No special-purpose centres (e.g., carbide-tipped bull-nose) are considered. Concept / Approach: The widely adopted standard included angle for lathe centres is 60°. This angle offers a good compromise between seating area and self-centering capability, minimizing deformation while supporting axial and radial loads during turning. Step-by-Step Solution: Identify the standard: 60° included angle.Check compatibility: centre drills and countersinks are also standardized to 60° to match.Conclude that the correct choice is 60°. Verification / Alternative check: Machine tool standards, centre drill geometry, and inspection gages reflect the 60° convention for most turning operations. Why Other Options Are Wrong: 30°/45°/90°/75°: nonstandard for general turning centres; would not match standard centre drills. Common Pitfalls: Confusing the included angle of centres (60°) with Morse taper angles used in spindles and tailstocks; these are unrelated geometric standards. Final Answer: 60°

Question 15

Effect of depth of cut on metal removal rate (MRR) In turning or similar machining operations, how does the material removal rate change when the depth of cut is increased (with all other parameters held constant)?

Accepted Answer

Introduction / Context: Material removal rate (MRR) is a primary productivity measure in machining. Knowing how speed, feed, and depth of cut affect MRR lets a process engineer balance cycle time against power, tool wear, and surface integrity. Given Data / Assumptions: Turning operation on a lathe (similar logic holds for many processes). Feed and cutting speed held constant; depth of cut is varied. Stable cutting without chatter or tool overload. Concept / Approach: For turning, a common expression is MRR = cutting speed * feed per revolution * depth of cut * constant (accounting for units and geometry). With speed and feed fixed, increasing depth of cut increases the uncut chip cross-sectional area linearly, therefore increasing MRR linearly—up to machine power and rigidity limits. Step-by-Step Solution: Hold speed and feed constant.Increase depth of cut → larger chip thickness across width → larger chip cross-section.MRR increases proportionally to depth of cut. Verification / Alternative check: Power consumption and cutting force rise with depth of cut; this correlates with higher MRR. Machine power charts show permissible depth increases until reaching spindle/drive limits. Why Other Options Are Wrong: Decreased/Unchanged: contradicts the geometric definition of MRR.Zero after a limit: not physically meaningful in normal ranges.Non-linear/unpredictable: under steady conditions the relation is straightforward. Common Pitfalls: Pushing depth too far can cause chatter, poor finish, or tool breakage; productivity gains must be balanced with tool life and machine rigidity. Final Answer: Increased

Question 16

Grinding wheel grade and grain retention A grinding wheel is said to be of which grade if its abrasive grains are relatively easy to dislodge from the bond during operation?

Accepted Answer

Introduction / Context: Grinding wheel performance depends on grit size, bond type, structure, and grade. Among these, grade expresses how strongly the bond holds the abrasive grains (i.e., wheel hardness in the grinding sense, not the grain’s mineral hardness). Given Data / Assumptions: Conventional vitrified or resinoid bonded wheels. Steady grinding with proper dressing and coolant. Focus on the definition of grade (holding power), not grit size or structure. Concept / Approach: A “soft grade” wheel releases dull grains readily, exposing fresh sharp edges and avoiding glazing. This is helpful when grinding hard materials or when self-sharpening is desirable. A “hard grade” wheel retains grains longer, which can be useful on softer materials to avoid rapid wear but risks glazing. Step-by-Step Solution: Define grade: measure of bond holding strength on abrasive grains.Identify property: easy dislodging of grains indicates weaker holding → soft grade.Conclude the correct option is “Soft grade.” Verification / Alternative check: Manufacturer catalogs and standards list grade letters (softer to harder). Recommendations match material hardness and wheel loading tendencies. Why Other Options Are Wrong: Medium/Hard/Super-hard: imply stronger grain retention, contrary to the statement.Open structure: spacing between grains; not a measure of bond holding strength. Common Pitfalls: Confusing grit size (coarse/fine) and structure (open/dense) with grade; each affects performance differently and must be selected together. Final Answer: Soft grade

Question 17

In a shaper, during which stroke is metal actually removed? Consider the standard quick-return shaper mechanism. Identify the stroke during which cutting takes place and chips are formed.

Accepted Answer

Introduction / Context: A shaper produces flat surfaces by reciprocating a single-point tool over a stationary work. The quick-return mechanism makes the non-cutting return stroke faster to reduce idle time. Given Data / Assumptions: Conventional shaper with clapper box on the tool head. Tool set with proper rake and clearance angles. Feed is given at the end of each cycle. Concept / Approach: In a typical shaper, cutting is performed during the forward stroke. The clapper box allows the tool to lift or swing slightly on the return stroke to avoid rubbing against the newly machined surface, thus no cutting occurs on the return stroke. The quick-return linkage ensures the return is faster than the forward cutting stroke, improving productivity. Step-by-Step Solution: Observe tool motion: tool engages the work during forward motion → chip forms.During return, clapper lifts the tool edge to prevent contact → no cutting.Therefore, metal is removed during the forward stroke only. Verification / Alternative check: Manufacturer cycle diagrams show feed increment after the return stroke, confirming forward-only cutting. Why Other Options Are Wrong: Return stroke: non-cutting by design.Both/Neither: contradicts shaper operating principle.Clapper orientation: assists non-contact return but does not change which stroke cuts. Common Pitfalls: Setting tool incorrectly so it rubs on return stroke; failing to secure the clapper can mar the surface or chip the tool. Final Answer: Forward stroke

Question 18

Key characteristics of Electrical Discharge Machining (EDM) Which of the following statements correctly describe EDM as a non-traditional machining process?

Accepted Answer

Introduction / Context: Electrical Discharge Machining (EDM) removes material by controlled spark discharges between an electrode and a conductive workpiece submerged in a dielectric. It is widely used for tooling, dies, and hard alloys that are difficult to machine conventionally. Given Data / Assumptions: Workpiece is electrically conductive (e.g., tool steel, carbides with cobalt binder). Appropriate dielectric fluid (e.g., kerosene, deionized water) and pulse generator are used. Process parameters are tuned to balance removal rate and finish. Concept / Approach: EDM relies on electrical discharges that locally melt and vaporize minute craters; there is no macroscopic cutting force and no mechanical contact. Because hardness does not prevent electrical erosion, EDM readily machines hardened steels and superalloys. With fine finishing pulses and optimized flushing, excellent surface finishes and complex cavities are achievable. Step-by-Step Solution: Check hardness capability: EDM is indifferent to mechanical hardness → can machine hardest conductive materials.Check finish/complexity: pulsed control and shaped electrodes allow fine finishes and intricate geometries.Check contact: erosion occurs across a spark gap; there is no mechanical rubbing or cutting. Verification / Alternative check: EDM process descriptions consistently emphasize spark gap control, crater formation, and lack of cutting forces as defining features. Why Other Options Are Wrong: Choosing any single statement alone underrepresents EDM; all listed statements are concurrently true. Common Pitfalls: Attempting to EDM non-conductive ceramics; neglecting electrode wear compensation; poor flushing causing arcing and surface damage. Final Answer: All of these

Question 19

Milling direction where cutting force starts maximum and ends minimum Identify the milling mode in which the instantaneous chip thickness starts at its maximum value when the tooth first engages the work and reduces toward minimum at exit.

Accepted Answer

Introduction / Context: The direction of cutter rotation relative to table feed defines up (conventional) or down (climb) milling. This choice affects chip thickness variation during a tooth’s engagement, which in turn influences force, finish, and tool life. Given Data / Assumptions: Standard slab or face milling engagement. Properly controlled backlash (e.g., CNC or well-maintained machine). Work is rigidly fixtured. Concept / Approach: In down (climb) milling, cutter rotation and feed are in the same direction at the point of contact. The tooth bites into the work with the largest chip thickness at entry and exits with near-zero thickness. This lowers rubbing at entry and can improve finish, provided backlash is managed. In up milling, the chip thickness starts at nearly zero and increases to maximum at exit. Step-by-Step Solution: Relate engagement geometry: “maximum at entry → minimum at exit” corresponds to climb milling.Name the process correctly: down milling (climb milling).Explain benefit: reduced rubbing and potential for better finish. Verification / Alternative check: Chip thickness sketches from machining texts clearly show the opposite progression for up vs. down milling. Why Other Options Are Wrong: Up milling: chip starts at zero and ends at maximum; opposite trend.Face/End milling: refer to cutter orientation, not chip-thickness progression.Slotting: an operation type; does not specify direction relationship. Common Pitfalls: Attempting climb milling on worn machines can cause part pull-in. Always minimize backlash and secure the work. Final Answer: Down milling (climb milling)

Question 20

End-of-life indicators for cutting tools in production machining  In practical shop practice, a tool is considered to have reached the end of its useful life when which of the following symptoms appear during cutting?

Accepted Answer

Introduction / Context: Tool life is a central concept in machining economics and quality control. In turning, milling, drilling, and grinding, a cutting edge gradually deteriorates until it can no longer maintain required accuracy, finish, or productivity. Recognizing the practical end-of-life indicators helps prevent scrap, spindle overloads, and unsafe conditions. Given Data / Assumptions: Conventional metal cutting with either high speed steel or cemented carbide tools. Machine tools operating at steady feeds, speeds, and depths of cut. End-of-life is determined by process performance, not solely by microscopic wear measurements. Concept / Approach: As wear increases (flank wear, crater wear, notch wear), cutting mechanics deteriorate. Friction rises along the tool–chip and tool–work interfaces, increasing power draw and temperature. The worn edge rubs instead of shearing cleanly, degrading surface finish. These symptoms appear together near the end of useful life, prompting tool indexing or replacement. Step-by-Step Solution: Identify practical indicators: surface finish, power/force spikes, and visible smoke or discoloration from overheating.Relate each to wear: higher friction from dull edges → higher forces → more heat → oxidation/smoke and poor finish.Conclude that the simultaneous presence of these symptoms defines end-of-life in shop practice. Verification / Alternative check: Maintenance logs often show power trends rising shortly before scheduled tool changes. Surface profilometer readings degrade as flank wear approaches its limit (e.g., a specified wear land width). Operators also note audible changes (squeal) and visible sparking/smoke at failure. Why Other Options Are Wrong: Poor surface finish alone (A) can arise from chatter or setup error; it is only one indicator. Force/power spikes alone (B) can also result from chip packing or coolant loss. Overheating/fuming (C) is a late symptom but not the only one. Only dimensional drift (E) ignores the coupled thermal and frictional effects typical at end-of-life. Common Pitfalls: Waiting for catastrophic edge failure; attributing rising power solely to material variability; ignoring coolant flow and chip evacuation, which can accelerate wear symptoms. Final Answer: all of the above

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