Q: Electrical Discharge Machining (EDM) applications in manufacturing EDM is best suited for non-traditional removal on hard or difficult-to-machine materials. Which of the following practical applications correctly reflects where EDM is commonly appl…

Introduction / Context: Electrical Discharge Machining (EDM) is a non-traditional machining process that removes material by a series of rapidly recurring electrical discharges (sparks) between an electrode tool and a conductive workpiece. It is particularly valuable for creating intricate shapes in very hard materials where conventional cutting fails or becomes uneconomical. Given Data / Assumptions: The workpiece and tool are electrically conductive. Material removal occurs by localized melting and vaporization in a dielectric fluid. Goal: identify typical industrial applications of EDM. Concept / Approach: Because EDM does not rely on mechanical cutting forces, it can machine hard carbides, tool steels, superalloys, and delicate features without inducing large stresses. Its strengths include producing complex cavities, fine holes, and detailed markings with excellent dimensional control. Step-by-Step Solution: Match EDM capability to application: hard carbides/tool steels → die and punch shaping.Assess small-hole drilling: EDM (including fast-hole EDM) produces numerous precise micro-holes in nozzles and sieves.Consider surface detail: spark erosion enables embossing/engraving on hard substrates.Hence, all listed uses are valid → choose “all of these”. Verification / Alternative check: EDM dies and molds are industry standards; aerospace fuel injector orifices and turbine cooling holes frequently use EDM drilling; engravings on hardened components are routinely spark-machined. Why Other Options Are Wrong: Option (E) mentions soft plastics and HSS cutters—this relates to conventional machining, not EDM, and plastics are typically non-conductive. Common Pitfalls: Forgetting the conductivity requirement; assuming EDM is fast for bulk removal (it is slower than conventional machining for large stock removal); neglecting recast layer and the need for post-processing in high-spec components. Final Answer: all of these

Question 1

Grinding wheels: “Dressing” and “truing” often use the same tools (e.g., diamond dresser) but serve different purposes. Do you agree with this statement?

Accepted Answer

Introduction / Context: Grinding wheel maintenance ensures consistent geometry and cutting action. Two routine operations—truing and dressing—are sometimes conflated, yet they address different issues: geometric accuracy versus cutting sharpness. Given Data / Assumptions: Abrasive wheel used on a standard grinder. Diamond dressing tools or rotary dressers are available. Wheel has experienced wear, potential runout, and glazing. Concept / Approach: Truing = restoring wheel geometry (roundness, concentricity, and face flatness) to remove runout.Dressing = renewing the wheel surface by fracturing abrasive grains and removing bond bridges to expose sharp cutting edges.While both may use the same diamond tool, the intent and setup differ. After heavy truing, a dressing pass is often applied to restore cutting efficiency. Step-by-Step Solution: Assess wheel: check runout and face geometry → decide if truing is needed.Apply truing to correct geometry; adjust until the wheel runs concentric and flat.Dress the wheel lightly to open the face and create the desired surface condition. Verification / Alternative check: Manufacturers’ recommendations and shop manuals explicitly separate the objectives of truing (geometry) and dressing (sharpness/porosity conditioning). Why Other Options Are Wrong: “Disagree” variants: the distinction applies across common bond types; both operations can use the same tools but target different outcomes. Common Pitfalls: Skipping truing when runout exists, expecting dressing alone to fix geometry; over-dressing which shortens wheel life; neglecting coolant and proper dresser traverse. Final Answer: Agree

Question 2

Lathe taper turning methods: The tailstock set-over method is best suited for which kind of taper?

Accepted Answer

Introduction / Context: Several methods can generate tapers on a lathe: compound rest swiveling, taper attachment, form tools, and tailstock set-over. Each has a best-fit use case regarding taper length, angle, rigidity, and finish. Given Data / Assumptions: Taper turning on a conventional engine lathe. Work held between centers so the tailstock can be offset. Need to maintain good surface finish over a long length. Concept / Approach: The tailstock set-over method offsets the tailstock centerline by a small amount, causing the workpiece axis to be inclined relative to the carriage motion. This naturally produces a gentle taper along the full length between centers, ideal for long, slender external tapers where small taper angles and good support are needed. Step-by-Step Solution: Recognize that the method requires work between centers → external turning.Small offset suits gentle (not steep) tapers over considerable length.Therefore the best fit is long, slender external tapers. Verification / Alternative check: Handbooks indicate compound rest is quicker for short/steep tapers; taper attachment for precise control; set-over for long mild tapers with full center support. Why Other Options Are Wrong: Internal tapers: set-over does not suit boring operations well.Small/steep short tapers: compound rest or form tool is more efficient and precise. Common Pitfalls: Excessive offset causing center loading and poor finish; forgetting to realign the tailstock afterward. Final Answer: Long, slender external tapers

Question 3

Boring tool height effect: Setting an internal boring tool above the spindle centerline primarily causes which change in effective angles?

Accepted Answer

Introduction / Context: Tool setting height relative to the work centerline changes the geometry seen at the cutting edge. In boring (an internal turning operation), improper height can alter effective rake and clearance, influencing cutting forces, chip flow, and surface finish. Given Data / Assumptions: Internal boring with a single-point tool at nominal geometry. Small offsets relative to center height. Conventional right-hand tool and standard spindle rotation. Concept / Approach: Moving the tool above the centerline rotates the effective cutting wedge relative to the work. Geometrically, this tends to increase the effective rake angle (tool appears “sharper”), while reducing the effective clearance angle (greater risk of rubbing if excessive). The converse occurs if the tool is set below center. Step-by-Step Solution: Visualize the cutting wedge at the bore surface.Shift tool above center → edge meets work with a more open rake.At the same time, the heel of the tool approaches the work → reduced clearance.Therefore, the change is: rake ↑, clearance ↓. Verification / Alternative check: Sketching the tool at different heights relative to the bore center confirms the angular changes; shop practice warns about rubbing when boring tools are set too high. Why Other Options Are Wrong: Options showing rake ↓ with tool above center contradict the standard geometric effect.“No significant change” ignores the real geometric sensitivity to height. Common Pitfalls: Setting the tool so high that clearance vanishes, causing chatter or poor finish; misreading external vs. internal turning geometry. Final Answer: Increase in effective rake angle and decrease in effective clearance angle

Question 4

Taylor tool life concept: As cutting speed increases (with other variables fixed), tool life typically __________.

Accepted Answer

Introduction / Context: Tool life behavior with speed is central to process planning. The classic Taylor tool life equation captures the inverse relationship between cutting speed and tool life for a given tool-work combination and set of cutting parameters. Given Data / Assumptions: All else constant: feed, depth of cut, tool geometry, coolant usage. Defined tool life criterion (e.g., flank wear land width). Steady turning or similar machining process. Concept / Approach: Taylor relationship: V * T^n = C, where V is cutting speed, T is tool life, n and C are empirical constants. Holding C and n fixed, an increase in V must be offset by a decrease in T, i.e., tool life falls as cutting speed rises. Step-by-Step Solution: Start with V * T^n = C.Increase V → to keep C constant, T^n must decrease → T decreases.Therefore, tool life decreases as speed increases. Verification / Alternative check: Plotting log V vs. log T gives a straight line with negative slope (−n), confirming the inverse relationship across tested conditions. Why Other Options Are Wrong: Increases/Remains constant: contradicts Taylor’s well-established empirical law.First increases then decreases: not typical for fixed conditions; anomalies usually stem from changing wear mechanisms or cooling. Common Pitfalls: Ignoring that feed and depth also affect life; assuming the same constants apply when changing tool materials or coatings. Final Answer: decreases

Question 5

Nontraditional machining: Chemical milling is performed by which basic arrangement?

Accepted Answer

Introduction / Context: Chemical milling (a nontraditional process) removes metal by controlled chemical dissolution. It is used to lighten components, create shallow pockets, and adjust thickness without conventional cutting forces or chip formation. Given Data / Assumptions: Workpiece material is chemically etchable with a selected reagent. Maskants protect areas not to be etched. Process controls include time, temperature, agitation, and concentration. Concept / Approach: Unlike mechanical milling, chemical milling occurs in a bath or spray etch chamber. The masked workpiece is immersed or sprayed, and the exposed regions dissolve at a controlled rate, producing the desired cavity depth or thinning. Step-by-Step Solution: Select compatible chemical etchant for the alloy.Apply maskant and pattern; bake/cure as required.Immerse or spray-etch in the tank for a calibrated time to achieve target metal removal. Verification / Alternative check: Industry practices (aerospace, electronics) use dip or spray etching lines, not conventional milling machines, for chemical milling and photochemical machining. Why Other Options Are Wrong: Conventional milling machines use cutters, not etchants; they cannot perform chemical milling. Common Pitfalls: Underestimating undercut and edge effects; poor masking leading to dimensional errors; inadequate neutralization and waste handling. Final Answer: In a tank containing an appropriate etching (chemical) solution

Question 6

Turning forces: The thrust (feed) force generally increases with an increase in which parameter, all else being equal?

Accepted Answer

Introduction / Context: In orthogonal and oblique cutting, the cutting force components (tangential, radial, and feed/thrust) depend on geometry and cutting conditions. Understanding how tool nose radius affects thrust helps balance surface finish against loading. Given Data / Assumptions: Turning with a single-point tool at fixed speed, feed, and depth of cut. Only one geometry variable is changed at a time. Work and tool materials remain constant. Concept / Approach: Increasing nose radius increases the contact length between tool and work and enlarges the ploughing zone at small feeds. This raises the radial and thrust components even as it can improve surface finish and edge strength. In contrast, increasing positive rake generally reduces forces; changes to side/end cutting edge angles have subtler, directional effects. Step-by-Step Solution: Hold cutting parameters constant.Increase tool nose radius → larger tool–work contact area → greater ploughing → higher thrust force.Conclusion: thrust increases with nose radius (other factors fixed). Verification / Alternative check: Force dynamometer data commonly show feed/thrust rising with nose radius at low to moderate feeds due to increased edge contact and burnishing. Why Other Options Are Wrong: Side/End cutting edge angles: influence chip flow direction and distribution but do not consistently raise thrust as nose radius does.Rake angle: a higher positive rake typically lowers all force components. Common Pitfalls: Using an excessively large nose radius at light feeds can cause chatter due to higher radial forces; always match radius to feed and rigidity. Final Answer: Tool nose radius

Question 7

Nose radius effects: Which statement about increasing the tool nose radius is most accurate?

Accepted Answer

Introduction / Context: The tool nose radius is a key finishing parameter. A larger radius can strengthen the cutting edge and smooth the feed marks, but it may also increase certain force components. This trade-off must be managed for stability and finish goals. Given Data / Assumptions: Turning with constant speed, feed, and depth of cut. Incremental changes to nose radius only. Stable machine and rigid setup. Concept / Approach: A greater nose radius distributes stresses over a larger edge area, reducing localized wear and chipping, thereby improving tool life. It also blends feed marks, yielding a smoother surface. However, thrust and radial forces may rise, so excessive radius at light feeds can lead to chatter. Step-by-Step Solution: Increase nose radius → edge becomes stronger → reduced wear and chipping → longer life.Increase nose radius → larger blending radius across feed scallops → better surface finish.Therefore, both benefits (tool life and finish) generally improve. Verification / Alternative check: Surface roughness models show Ra roughly proportional to (feed^2)/(32 * nose radius) for finishing, indicating finish improves as radius increases. Why Other Options Are Wrong: Only (a) or only (b): understate the dual effect.“Always reduces cutting forces”: incorrect; thrust/radial forces often increase with larger radius. Common Pitfalls: Using too large a radius on a flexible setup; mismatch between radius and feed causing chatter or poor chip control. Final Answer: Both (a) and (b)

Question 8

Drill geometry selection: The preferred point angle for drilling stainless steel is typically ________.

Accepted Answer

Introduction / Context: Stainless steels are tough and work-harden readily, demanding robust drill geometry to reduce chisel edge thrust and improve penetration. Point angle choice directly affects cutting action and heat generation. Given Data / Assumptions: A standard twist drill is used (not a split-point or special geometry). Appropriate cutting fluid is applied. Machine rigidity and feeds/speeds are suitable for stainless steel. Concept / Approach: Larger point angles (e.g., 135°) create a shorter chisel edge and a stronger point, which helps when drilling tough, work-hardening materials. General-purpose drills for mild steel often use 118°, but stainless benefits from 135° with proper lip relief and possibly split-point to lower thrust and wandering. Step-by-Step Solution: Identify material: stainless → tough/work-hardening.Select larger point angle to strengthen the point and reduce thrust → 135°.Confirm suitability with appropriate speed, feed, and coolant. Verification / Alternative check: Machining handbooks routinely recommend 135° for tough alloys including stainless, often combined with split-point geometry. Why Other Options Are Wrong: 90°/100°: too acute for stainless; weak point and increased wandering.118°: common for mild steel, but not optimal for stainless.150°: excessive and may increase rubbing without special setups. Common Pitfalls: Running too fast causing work-hardening; inadequate coolant; dull drills leading to burnishing rather than cutting. Final Answer: 135°

Question 9

Tool materials: Stellite (cobalt-base alloy) preserves its hardness up to approximately what temperature?

Accepted Answer

Introduction / Context: Hot (red) hardness indicates a tool material’s ability to retain hardness at elevated temperature. Stellite, a cobalt-based alloy with chromium and tungsten, bridges the gap between high-speed steels and carbides for heat resistance and wear properties in certain applications. Given Data / Assumptions: Comparative ranges: HSS retains hardness roughly up to 550–650°C, stellite higher, straight carbides even higher (near 1000–1100°C depending on grade and binder). Conventional cutting without advanced coatings. Concept / Approach: Stellite grades exhibit very good hot hardness and abrasion resistance, retaining useful hardness up to about 850–900°C. This makes them suitable for high-temperature cutting of hard or scale-forming materials where HSS softens, though carbides usually surpass both for high-speed conditions. Step-by-Step Solution: Identify typical hot hardness plateaus: HSS < stellite < carbide.Stellite’s practical upper range ≈ 900°C for preserving hardness.Select 900°C as the best match among choices. Verification / Alternative check: Toolmaterial data sheets list stellite hot-hardness resistance around the stated range, aligning with shop experience in hard, hot cutting tasks. Why Other Options Are Wrong: 350°C/500°C: too low; even HSS exceeds these limits.1100°C: characteristic of certain carbides/ceramics rather than stellite.650°C: closer to HSS red-hardness region. Common Pitfalls: Confusing stellite with cemented carbide; overlooking that selection also depends on toughness, not only hot hardness. Final Answer: 900°C

Question 10

Electrical Discharge Machining (EDM) applications in manufacturing  EDM is best suited for non-traditional removal on hard or difficult-to-machine materials. Which of the following practical applications correctly reflects where EDM is commonly appl…

Accepted Answer

Introduction / Context: Electrical Discharge Machining (EDM) is a non-traditional machining process that removes material by a series of rapidly recurring electrical discharges (sparks) between an electrode tool and a conductive workpiece. It is particularly valuable for creating intricate shapes in very hard materials where conventional cutting fails or becomes uneconomical. Given Data / Assumptions: The workpiece and tool are electrically conductive. Material removal occurs by localized melting and vaporization in a dielectric fluid. Goal: identify typical industrial applications of EDM. Concept / Approach: Because EDM does not rely on mechanical cutting forces, it can machine hard carbides, tool steels, superalloys, and delicate features without inducing large stresses. Its strengths include producing complex cavities, fine holes, and detailed markings with excellent dimensional control. Step-by-Step Solution: Match EDM capability to application: hard carbides/tool steels → die and punch shaping.Assess small-hole drilling: EDM (including fast-hole EDM) produces numerous precise micro-holes in nozzles and sieves.Consider surface detail: spark erosion enables embossing/engraving on hard substrates.Hence, all listed uses are valid → choose “all of these”. Verification / Alternative check: EDM dies and molds are industry standards; aerospace fuel injector orifices and turbine cooling holes frequently use EDM drilling; engravings on hardened components are routinely spark-machined. Why Other Options Are Wrong: Option (E) mentions soft plastics and HSS cutters—this relates to conventional machining, not EDM, and plastics are typically non-conductive. Common Pitfalls: Forgetting the conductivity requirement; assuming EDM is fast for bulk removal (it is slower than conventional machining for large stock removal); neglecting recast layer and the need for post-processing in high-spec components. Final Answer: all of these

Question 11

Jigs vs fixtures in production tooling  Consider the statement: “Jigs are heavier than fixtures in construction.” Choose the correct evaluation.

Accepted Answer

Introduction / Context: In manufacturing, jigs and fixtures are special-purpose tools that improve productivity, accuracy, and interchangeability. Understanding their differences helps select the right device for drilling, milling, turning, and other operations. Given Data / Assumptions: A jig both locates/holds the work and guides the tool (e.g., drill jig). A fixture locates/holds the work but does not guide the tool (e.g., milling fixture). Heavier construction is needed where cutting forces are higher. Concept / Approach: Fixtures are typically used in operations with larger cutting forces (milling, turning, grinding). They must resist bending, vibration, and cutting loads, leading to robust, heavier designs. Jigs, common in drilling, reaming, and tapping, guide the tool with bushings and are usually lighter because forces are relatively lower. Step-by-Step Solution: Identify functional difference: jigs guide tools; fixtures do not but must withstand heavy forces.Relate to structural design: heavier bodies are needed to resist milling/turning loads → fixtures tend to be heavier.Evaluate statement: “Jigs are heavier than fixtures” is incorrect. Verification / Alternative check: Practical shop tooling shows simple plate or box jigs (relatively light) versus bulky milling fixtures and tombstones designed to absorb high loads. Why Other Options Are Wrong: (C), (D), and (E) add conditions unrelated to the fundamental distinction; material choice and batch size do not overturn the general rule that fixtures are heavier. Common Pitfalls: Confusing the presence of guide bushings (jigs) with mass; assuming all precision devices must be heavy; overlooking operational cutting loads. Final Answer: No

Question 12

Standard spindle taper used on drilling machines  The drill spindles on conventional drilling machines are commonly provided with which standard taper?

Accepted Answer

Introduction / Context: Tapers allow self-holding, accurate alignment, and quick tool changes in machine tools. Drilling machines around the world largely standardize on a particular taper for compatibility of spindles, sleeves, and drill shanks. Given Data / Assumptions: General-purpose pillar, radial, and bench drills. Self-holding taper fits without drawbar for typical sizes. Concept / Approach: The Morse taper series (MT1–MT7) is the de facto standard for drill spindles and shanks due to its self-holding characteristic, ease of ejection with drift slots, and broad availability. Other tapers exist in machine-tool practice but are not the predominant standard for drill spindles. Step-by-Step Solution: Identify common practice: drills and sleeves marked MT numbers.Confirm self-holding design suits drilling thrust loads.Select “Morse taper” as the standard. Verification / Alternative check: Tooling catalogs, drill sleeves, and spindle specifications consistently reference Morse tapers. Why Other Options Are Wrong: Seller’s, Chapman, Brown & Sharpe, and Jarno tapers exist but are less common for drill spindles in modern general-purpose drilling equipment. Common Pitfalls: Confusing milling spindle tapers (e.g., CAT/BT, R8) with drilling tapers; mixing Morse taper numbers with taper-per-foot specifications of other standards. Final Answer: Morse taper

Question 13

Comparing drilling cutting speeds: materials and tool type  The recommended cutting speed for drilling aluminium, brass, and bronze using carbon steel drills is _________ the cutting speed for drilling mild steel using high-speed steel (HSS) drills.

Accepted Answer

Introduction / Context: Cutting speed selection depends on both the work material and the tool material. Although aluminium and brasses are softer than steels, the thermal limits of carbon steel drills are much lower than those of high-speed steel (HSS), which constrains allowable speed. Given Data / Assumptions: Carbon steel (CS) drills have poor hot hardness; HSS has superior hot hardness. Work materials: aluminium/brass/bronze versus mild steel. Comparison requested: CS-on-soft metals vs HSS-on-mild steel. Concept / Approach: Allowable cutting speed is limited by tool material’s ability to maintain hardness at temperature. Even though non-ferrous materials often permit high speeds, carbon steel drills overheat quickly. HSS on mild steel commonly runs at higher speeds than CS on non-ferrous metals due to HSS’s thermal capability. Step-by-Step Solution: Set baseline: typical HSS drilling of mild steel uses higher surface speeds than CS can sustain on any material.Account for material softness: aluminium/brass would allow high speeds, but tool constraint (CS) dominates.Therefore, CS-on-Al/Br/Brz speed is less than HSS-on-MS speed. Verification / Alternative check: Typical charts: HSS on mild steel may allow substantially higher m/min than CS on aluminium; CS recommendations are conservative to avoid tempering loss. Why Other Options Are Wrong: (A) Equal ignores tool material effect; (C) More than misreads tool limitation; (D) and (E) contradict fundamental machining principles. Common Pitfalls: Assuming work material softness alone decides speed; overlooking tool material thermal limits; ignoring coolant and feed interactions. Final Answer: less than

Question 14

Classification of broaching motions  In which broaching arrangement does the workpiece move past a stationary multi-tooth tool to achieve rapid, continuous production?

Accepted Answer

Introduction / Context: Broaching removes material with a multi-tooth tool where each successive tooth removes a small additional chip. Different machine configurations suit internal, external, or surface features and varying production rates. Given Data / Assumptions: Stationary vs moving tool setups. Production emphasis on continuous throughput. Concept / Approach: In continuous broaching, the broach is held stationary while parts move continuously (often on a conveyor or chain), passing across the tool to machine surfaces at high rates. This contrasts with pull/push broaching where the tool travels through or over stationary work, and with surface broaching where the tool typically traverses the work but not necessarily in a continuous production line. Step-by-Step Solution: Identify motion: work moves; tool stationary.Associate with production: continuous transfer of parts → continuous broaching.Therefore, select “continuous broaching”. Verification / Alternative check: Automotive lines employ continuous broaching for high throughput on flats, slots, and profiles. Why Other Options Are Wrong: Pull/push broaching move the tool, not the work, in discrete strokes; surface broaching describes the feature type rather than the continuous transfer-line method; rotary swaging is a forming process, not broaching. Common Pitfalls: Confusing feature type (surface vs internal) with the production mode (continuous); assuming all broaching requires tool motion only. Final Answer: continuous broaching

Question 15

Function of the half-nut on a lathe  Evaluate the statement: “Half nut is used to lock the lathe carriage to the lead screw for thread cutting.”

Accepted Answer

Introduction / Context: Accurate thread cutting on a lathe requires synchronizing carriage motion with spindle rotation via the lead screw. The half-nut mechanism is central to engaging and disengaging this drive precisely. Given Data / Assumptions: Engine/centre lathe with lead screw and feed rod. Half-nuts mounted in the apron clamp around the lead screw. Concept / Approach: When the operator closes the half-nuts, the carriage couples directly to the lead screw’s helix, converting screw rotation into precise linear travel for thread cutting. Disengaging the half-nuts disconnects the carriage from the lead screw to stop or retract. Step-by-Step Solution: Identify purpose: synchronize carriage feed with spindle via gear train and lead screw.Engage half-nuts: secure carriage to lead screw for the threading pass.Therefore, the statement is true. Verification / Alternative check: Lathe apron diagrams show separate clutches for power feeds (via feed rod) versus half-nuts for threading (via lead screw). Why Other Options Are Wrong: (B) and (E) contradict standard lathe design; (C) and (D) add unnecessary conditions—thread type and speed do not change the core function of half-nuts. Common Pitfalls: Confusing feed-rod driven power feed with lead-screw threading; opening half-nuts mid-pass causing pitch errors; mis-timing re-engagement on metric threads when using an imperial lead screw. Final Answer: True

Question 16

Selecting a finishing process for a surface roughness of 0.75 µm to 1.25 µm (Ra)  Which manufacturing process is typically used to achieve a surface finish within 0.75 µm to 1.25 µm on cylindrical bores or surfaces?

Accepted Answer

Introduction / Context: Surface finish requirements drive the choice of finishing operations. Honing, grinding, lapping, and buffing each occupy a performance window in terms of achievable roughness and geometry control. Given Data / Assumptions: Target roughness range: approximately 0.75 µm to 1.25 µm Ra. Typical applications include hydraulic cylinders, engine liners, and precision bores. Concept / Approach: Honing uses low cutting speeds and bonded abrasive sticks with a reciprocating, expanding tool to correct form errors and impart a crosshatch surface. Its controllable stock removal and fine abrasive action make it ideal for finishes around 0.8–1.2 µm Ra. Grinding can reach near this range but is usually selected for slightly coarser to moderately fine finishes; lapping achieves much finer finishes; buffing is primarily cosmetic on external surfaces. Step-by-Step Solution: Map processes to finish ranges: grinding ~1.6–0.2 µm (varies), honing ~1.5–0.1 µm, lapping ~0.1–0.01 µm.Target lies well within honing’s sweet spot for bores.Select “honing”. Verification / Alternative check: Engine cylinder liners are honed to achieve oil-retaining crosshatch and controlled Ra within this range. Why Other Options Are Wrong: Grinding (A) may achieve the range but is less suited to correcting bore geometry and producing crosshatch; lapping (B) is typically finer; buffing (D) is for external shine, not precise bores; planing (E) is a roughing/forming method. Common Pitfalls: Confusing Ra targets for different components; assuming lapping is always required for high quality when honing suffices; overlooking geometric corrections offered by honing. Final Answer: honing

Question 17

Standard point angle for general-purpose twist drills  What is the usual included point angle for a standard general-purpose twist drill used on steels?

Accepted Answer

Introduction / Context: The point angle of a twist drill affects chisel edge length, thrust force, chip flow, and wear. A widely adopted standard exists for general-purpose drilling in steels and many other materials. Given Data / Assumptions: Conventional HSS twist drills for general shop use. No special-purpose geometry (e.g., split point, cobalt, or parabolic flutes). Concept / Approach: The most common point angle is 118°. It balances penetration and edge strength, producing reasonable thrust while allowing acceptable chip evacuation in many materials. Harder materials or specific applications may use 135° or other angles, but 118° remains the general baseline. Step-by-Step Solution: Identify general standard → 118°.Note variants (e.g., 135° split point) for tough materials, but that is not the “usual” case.Answer: 118°. Verification / Alternative check: Drill manufacturer catalogs and handbooks list 118° as the default point angle for general-purpose drills. Why Other Options Are Wrong: 70° and 100° are too small, increasing thrust and weakening lips; 130° or 150° are more specialized for hard alloys and reduce wandering but are not the default standard. Common Pitfalls: Confusing point angle with lip relief or helix angle; assuming one angle fits all materials without considering modifications. Final Answer: 118°

Question 18

Merchant’s force analysis assumptions in metal cutting  According to Merchant’s classical analysis of orthogonal cutting, which of the following assumptions are made?

Accepted Answer

Introduction / Context: Merchant’s force analysis provides foundational insight into chip formation, shear angle, and cutting forces in orthogonal cutting. The analysis relies on idealized assumptions to yield tractable relationships. Given Data / Assumptions: Orthogonal cutting model with a sharp tool. Steady-state cutting with a continuous chip. Defined friction along the rake face resulting in a resultant force. Concept / Approach: Key assumptions include a perfectly sharp tool with no flank contact, continuous chip (no built-up edge) to avoid transient effects, and constant cutting velocity for steady-state force balance. These yield the classic shear plane analysis and the Merchant shear-angle relation under a minimum energy criterion. Step-by-Step Solution: Evaluate (A): Sharp tool with no flank contact → assumed in the ideal model.Evaluate (B): Continuous chip, no BUE → steady-state simplifies analysis.Evaluate (C): Constant velocity → permits static force triangle and constant shear plane.Therefore, select “all of the above”. Verification / Alternative check: Textbook derivations explicitly list these simplifying assumptions before constructing force and velocity triangles. Why Other Options Are Wrong: (E) contradicts the assumption of a single resultant friction force at the rake face employed in the model. Common Pitfalls: Applying Merchant’s conclusions directly to interrupted cuts or built-up-edge conditions; ignoring tool wear and thermal effects not captured in the idealization. Final Answer: all of the above

Question 19

Buffing wheel composition for surface finishing  Buffing (polishing) wheels used in finishing operations are commonly made of which material?

Accepted Answer

Introduction / Context: Buffing is a finishing process used to improve luster and smoothness of surfaces after machining or grinding. The wheel material and applied compounds determine the final appearance and micro-roughness. Given Data / Assumptions: Common shop buffing wheels (not abrasive grinding wheels). Use of polishing compounds such as rouge, tripoli, or alumina. Concept / Approach: Buffing wheels are typically built from layers of cloth—most commonly cotton—stitched together to form a flexible face. The cotton holds and delivers polishing compound to the work, enabling gentle abrasion and plastic flow at the surface, producing a high shine. Step-by-Step Solution: Identify typical wheel structure: multiple plies of cotton cloth, stitched.Confirm function: carry compound and conform slightly to surface contours.Select “cotton fabric” as the correct material. Verification / Alternative check: Supplier catalogs list stitched cotton, loose-leaf cotton, and ventilated cotton buffs as standard options. Why Other Options Are Wrong: Metals (A) would scratch and are not used for buffing wheels; carbon/graphite (C/D) are not typical buffing wheel materials; glass fiber (E) relates to reinforced abrasive wheels rather than cloth buffs. Common Pitfalls: Confusing buffing (cloth + compound) with polishing using fixed abrasive wheels; using the wrong compound for the substrate leading to smearing or residue. Final Answer: cotton fabric

Question 20

Conventional milling (up milling): Which statement best describes a characteristic of up milling on a horizontal/vertical milling machine?

Accepted Answer

Introduction / Context: In conventional (up) milling, the worktable feeds against the direction of cutter rotation. This contrasts with climb (down) milling, where feed is in the same direction as rotation. The choice affects chip thickness evolution, cutting force direction, heat, and resulting surface finish. Understanding these differences is essential for selecting parameters and anticipating part quality. Given Data / Assumptions: Milling with a slab or end mill on a conventional machine with some mechanical backlash. Standard steels and aluminum alloys; no special cutters or serrated teeth assumed. Focus on qualitative behavior: chip formation, forces, finish, and coolant access. Concept / Approach: In up milling, chip thickness starts near zero and increases to a maximum at tooth exit. This rubbing-then-cutting sequence increases friction and can leave fine feed marks and a slightly wavy surface relative to down milling, where chip thickness starts thick and decreases, often giving a cleaner shearing action and better finish on rigid machines. Step-by-Step Solution: Identify chip thickness trend in up milling → thin-to-thick.Infer higher rubbing at entry → more heat, potential smearing, and fine waviness.Compare with down milling → typically better finish on tight/rigid machines. Verification / Alternative check: Process handbooks and shop experience consistently report that down milling often produces improved finish due to better chip formation, provided backlash is controlled. Up milling is preferred when backlash could cause self-feeding problems in down milling. Why Other Options Are Wrong: The chips are disposed of easily…: chip evacuation depends on setup; this statement is more typical of down milling where chips are swept behind the cut. Cannot be used on older machines: actually down milling is the one risky on machines with backlash; up milling is safer. Coolant always reaches the max-force zone: tooth entry in up milling involves rubbing; coolant access is intermittent. Cutter forces always push work down: in up milling, vertical components can lift the work, not always push it down. Common Pitfalls: Assuming finish is always the same for up and down milling; ignoring machine backlash and rigidity; confusing chip flow direction between the two processes. Final Answer: The milled surface quality tends to be slightly wavy compared with down milling.

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