Question 1

Manufacturing process identification Which metal-cutting process removes material by pushing or pulling a multi-tooth cutting tool through (or across) a preformed hole or surface to generate accurate profiles in a single pass?

Accepted Answer

Introduction / Context: Broaching is a high-productivity machining process in manufacturing where a toothed tool (the broach) is either pushed or pulled across a workpiece. It is used to produce precise internal and external profiles such as keyways, splines, hex holes, and noncircular shapes in one continuous stroke. Given Data / Assumptions: The process under discussion uses a multi-tooth tool. Material removal occurs in a single pass with increasing tooth height (rise per tooth). Tool motion is linear (push or pull) rather than rotational. Concept / Approach: Each successive tooth on a broach removes a small additional layer of material. The combination of roughing, semi-finishing, and finishing teeth in one tool yields tight tolerances and excellent surface finish without multiple setups. Step-by-Step Solution: Identify processes that use push/pull motion with a multi-tooth tool → broaching.Confirm that milling (up/down) uses a rotating cutter, not a push/pull stroke → eliminate.Forming generally plastically deforms metal rather than chips it away → eliminate.Therefore, the correct answer is broaching. Verification / Alternative check: Common broaching applications include internal keyways and splines formed in a single stroke, confirming the push/pull nature and multi-tooth action. Why Other Options Are Wrong: Up/Down milling: chip removal by a rotating cutter; not a single linear push/pull stroke.Forming: plastic deformation, no chip removal.Slotting: reciprocating single-point cutting, not multi-tooth progressive tool. Common Pitfalls: Confusing broaching with slotting or shaping due to the linear motion; the defining difference is the multi-tooth progressive geometry. Final Answer: Broaching

Question 2

Machining heat generation — which mechanism dominates at the tool–chip interface? In metal cutting, the work–tool contact (chip–tool interface) is a major heat source primarily due to what phenomenon?

Accepted Answer

Introduction / Context: During machining, heat is generated in three regions: (1) the primary shear zone (plastic deformation), (2) the secondary deformation zone at the chip–tool interface (friction and some plastic deformation), and (3) the tertiary zone at the tool flank (rubbing/burnishing). Understanding which mechanism dominates at the work–tool contact helps in selecting tool materials and cutting fluids. Given Data / Assumptions: The “work–tool contact zone” here refers to the chip sliding over the rake face. Steady cutting, conventional speeds and feeds, typical ductile materials. Concept / Approach: At the rake face, the newly formed chip is at high temperature and pressure; it slides (or sticks–slides) over the tool, causing intense frictional heating. Although plastic deformation dominates in the primary zone, the specific zone asked is the tool–chip interface where friction is the principal source. Step-by-Step Solution: Identify the region: chip–tool contact on the rake face.Associate mechanism: sliding/sticking friction between chip and tool.Conclude: dominant heat source in that zone is friction. Verification / Alternative check: Temperature maps show peak temperatures near the tool–chip interface at high speeds, corroborating frictional origin. Why Other Options Are Wrong: Plastic deformation in the primary shear zone occurs ahead of the tool, not at the rake face interface.Burnishing on the machined surface is the flank region and contributes less heat than the rake face.Radiation and shank shear are negligible compared to frictional and plastic work. Common Pitfalls: Assuming the primary shear zone is always the hottest; at high speeds, the chip–tool interface often reaches the maximum temperature. Final Answer: Friction between the moving chip and the tool face

Question 3

Grinding machine selection Which grinder is best suited for machining irregular, curved, tapered, convex, and concave surfaces and for sharpening complex cutters?

Accepted Answer

Introduction / Context: Different grinding machines serve distinct geometries. Selecting the correct grinder impacts accuracy, finish, and productivity, especially for complex profiles and multi-edge cutting tools. Given Data / Assumptions: Need to grind irregular, curved, convex/concave, and tapered surfaces. Application includes sharpening of milling cutters, drills, reamers, and form tools. Concept / Approach: Tool and cutter grinders provide multi-axis motions (e.g., swiveling work head, tilting wheel head, and adjustable tables) enabling complex geometries and precise relief/clearance angles. Jigs and fixtures extend versatility. Step-by-Step Solution: Match required geometry complexity → requires multi-axis flexibility.Tool and cutter grinder offers necessary degrees of freedom and accessories.Other grinders specialize in simpler geometries (flat, cylindrical, or internal), hence less suitable. Verification / Alternative check: Manufacturers catalogues list tool and cutter grinders for sharpening helical and form cutters, confirming suitability. Why Other Options Are Wrong: Surface grinder: primarily for flat surfaces.Cylindrical grinder: external cylinders and shoulders.Internal grinder: internal bores.Centerless grinder: external cylindrical surfaces without centers; limited profiling. Common Pitfalls: Trying to produce complex cutter reliefs on a surface or cylindrical grinder; setups become impractical and inaccurate. Final Answer: Tool and cutter grinder

Question 4

Tool material characteristics Carbon tool steels exhibit low heat resistance and low wear resistance compared with HSS and carbides. Is this statement correct?

Accepted Answer

Introduction / Context: Tool material selection balances hot hardness, wear resistance, toughness, and cost. Carbon tool steels were historically common but are now limited to low-speed applications due to poor hot-strength and rapid softening at modest temperatures. Given Data / Assumptions: Carbon tool steels lose hardness rapidly above roughly 200–250 °C. Comparators: high-speed steel (HSS), cast/cemented carbides, ceramics. Operations: general cutting where heat generation is significant. Concept / Approach: Hot hardness describes a material's ability to retain hardness at elevated temperatures. Carbon tool steels temper easily and cannot maintain an edge under modern cutting speeds, leading to accelerated flank wear and built-up edge formation. Step-by-Step Solution: Assess heat resistance: carbon tool steels soften at relatively low temperatures → low heat resistance.Assess wear resistance: softening plus limited alloy carbides → poorer wear resistance than HSS/carbides.Conclusion: the statement is correct. Verification / Alternative check: Tool life curves (Taylor's equation) show dramatically lower permissible cutting speeds for carbon steels versus HSS/carbide for the same life. Why Other Options Are Wrong: Claiming incorrectness or exceptions (interrupted cuts, high temperatures) misunderstands the fundamental deficiency in hot hardness and wear resistance. Common Pitfalls: Using carbon tool steel where heat cannot be controlled; choose HSS or carbide for sustained industrial speeds. Final Answer: Correct

Question 5

Lathe spindle construction Lathe spindles are commonly made hollow and provided with which feature for accurate location of centers, arbors, and tooling?

Accepted Answer

Introduction / Context: Machine tool spindles must locate accessories precisely and transmit torque safely. In engine lathes, the headstock spindle is typically hollow to pass bar stock and to accept standard tooling. Given Data / Assumptions: Typical workshop/engine lathe. Use of centers, taper shank drills, arbors, and live centers. Concept / Approach: An internal self-holding taper (commonly Morse taper) inside the spindle nose ensures accurate, repeatable alignment for taper-shank tools and centers. The hollow spindle also allows long bars to pass through for production convenience. Step-by-Step Solution: Identify standard locating feature → internal Morse taper in spindle bore.Recognize purpose → quick, precise seating of taper shank tools and centers.Conclude that “internal taper” is correct. Verification / Alternative check: Manufacturer specifications for engine lathes list Morse taper numbers (e.g., MT4, MT5) for the headstock spindle. Why Other Options Are Wrong: External tapers are used on noses, sleeves, or tooling—not as the primary locating feature inside the spindle bore. A straight bore cannot firmly seat taper shanks without adapters. Common Pitfalls: Confusing spindle nose mounting standards (e.g., Camlock, A, L types) with the internal Morse taper; both can coexist for different purposes. Final Answer: Internal taper

Question 6

Definition precision — shear angle in orthogonal cutting In metal cutting theory, the shear angle is defined as the angle between the shear plane and which reference direction?

Accepted Answer

Introduction / Context: The shear angle is central in chip-formation mechanics. It appears in Merchant's analysis and affects chip thickness, cutting force, and heat generation. Given Data / Assumptions: Orthogonal cutting with a straight cutting edge normal to the cutting velocity. Shear occurs along a single shear plane. Concept / Approach: The shear angle φ is defined as the angle between the shear plane and the direction of cutting velocity. With chip thickness t_c, uncut chip thickness t_o, and rake angle α, the relationships include geometry and force models (e.g., Merchant's minimum energy criterion). Step-by-Step Solution: Establish cutting kinematics → velocity direction is tangential to workpiece motion past the tool.Define shear plane → plane along which primary plastic deformation concentrates.By definition, φ is measured from cutting velocity direction to the shear plane → correct reference is the direction of cutting velocity. Verification / Alternative check: Alternative equivalent definition uses 90° − φ as the angle between the shear plane and the work surface; hence choosing the work surface would be incorrect without that complement. Why Other Options Are Wrong: Work surface relates by complement (90° − φ), not φ itself. Tool rake face angle is α, not φ. Spindle axis and normal to work surface are unrelated reference directions for defining φ. Common Pitfalls: Interchanging φ with 90° − φ, leading to errors in chip-thickness ratio and force predictions. Final Answer: Direction of cutting velocity

Question 7

Grinding wheel selection for soft materials To grind comparatively soft materials efficiently without wheel loading, which grain size should be chosen?

Accepted Answer

Introduction / Context: Grinding wheel selection balances grain size, grade (hardness), structure, and bond. For soft materials, chip size and wheel self-sharpening behavior determine performance and risk of loading (clogging). Given Data / Assumptions: Material characterized as soft and gummy relative to wheel abrasives. Conventional abrasives (Al2O3, SiC) and standard bonds. Concept / Approach: Coarser grains provide larger chip pockets and stronger cutting points, promoting chip clearance and reducing wheel loading. Softer wheel grade is also typical so dull grains can release and expose new sharp edges. Step-by-Step Solution: Identify need: avoid loading and glazing on soft work materials.Select larger grit size → coarse grained wheel increases chip space.Combine with appropriate softer grade for self-sharpening. Verification / Alternative check: Grinding handbooks recommend coarse grit and open structure for soft, ductile metals to maintain cutting efficiency and surface finish. Why Other Options Are Wrong: Fine or ultra-fine grits have small chip spaces and quickly load up on soft materials; medium grit may still load. CBN selection depends on material (best for hardened steels), not merely softness. Common Pitfalls: Choosing a hard-grade, fine-grit wheel for soft metals results in glazing, burning, and rapid wheel wear. Final Answer: Coarse grained wheel

Question 8

Cemented carbide tool composition In cemented carbide (sintered carbides such as WC-based) cutting tools, which binder metal is typically used to cement the carbide grains?

Accepted Answer

Introduction / Context: Cemented carbides are composite tool materials consisting of hard carbide particles bonded by a metallic binder. They offer high hot hardness and wear resistance for modern machining. Given Data / Assumptions: Common systems: WC–Co, WC–TiC–Co, and additions like TaC, NbC. Application: turning, milling, drilling at higher speeds than HSS. Concept / Approach: Cobalt serves as the ductile metallic binder that cements tungsten carbide grains after powder pressing and sintering. Co content (e.g., 3–15%) tunes toughness versus wear resistance: higher Co improves toughness, lower Co improves hot hardness and wear. Step-by-Step Solution: Identify the matrix/binder in cemented carbides → cobalt.Recognize role: ductility, crack bridging, toughening of the brittle carbide skeleton.Conclude cobalt is the standard binder in WC-based carbides. Verification / Alternative check: Materials datasheets for ISO P/M/K carbides universally list Co as binder; alternative binders (Ni, Fe) exist for corrosion resistance but are less common in general-purpose cutting. Why Other Options Are Wrong: Tungsten is the primary carbide former (WC), not binder. Chromium and silicon are minor alloying/processing elements; molybdenum is used in some carbides and steels, not the primary binder. Common Pitfalls: Confusing cemented carbides with cermets (TiCN-based) or ceramics, which have different bonding mechanisms and properties. Final Answer: Cobalt

Question 9

Choose the correct grinding wheel grain size for soft materials Fill in the blank: A __________ grinding wheel is generally preferred for grinding soft materials to minimize loading and improve cutting action.

Accepted Answer

Introduction / Context: Wheel grit size determines chip accommodation and the aggressiveness of cutting points. For soft, ductile work materials, the tendency to smear and clog the wheel must be countered by appropriate grit selection. Given Data / Assumptions: Soft material (e.g., mild steel, aluminum alloys). Conventional vitrified or resinoid bonds. Concept / Approach: Coarse grains create larger chip spaces, reduce wheel loading, and promote a free-cutting action. This is often paired with a softer grade and more open structure to enhance self-sharpening. Step-by-Step Solution: Assess work material behavior → ductile, tends to load wheels.Select larger grit size → more chip clearance.Therefore, choose a coarse grained wheel. Verification / Alternative check: Shop practice and grinding handbooks recommend coarse grit/open structure for soft metals to avoid glazing. Why Other Options Are Wrong: Fine and dense wheels quickly load on soft materials; medium grit may still be inadequate. Extra-hard grades exacerbate glazing rather than prevent it. Common Pitfalls: Attempting to improve finish on soft metals with excessively fine grit; finish often worsens due to wheel loading and heat marks. Final Answer: Coarse grained

Question 10

Trepanning operation — correct definition In hole-making, trepanning is best described as which of the following operations?

Accepted Answer

Introduction / Context: Trepanning is a specialized hole-making method used to produce large-diameter holes efficiently by removing only an annular ring of material. It is common in plate fabrication and where core preservation is desired. Given Data / Assumptions: Goal: create relatively large holes in plates, pipes, or solid stock. Tool: hollow, circular cutter (trepanning tool or hole saw) guided about an axis. Concept / Approach: Instead of drilling out the entire cross-section, trepanning cuts the circumference and leaves a solid core. This reduces power consumption and chips compared to drilling a full solid, and the slug may be reused as a blank. Step-by-Step Solution: Identify process that removes metal only along the periphery → trepanning.Contrast with reaming (sizing) and spot facing (squaring around a hole).Conclude the correct description: producing a hole with a hollow cutting tool removing an annulus. Verification / Alternative check: Power calculations show reduced torque for trepanning vs. drilling same diameter, validating the operational definition. Why Other Options Are Wrong: Spot facing and chamfering shape the mouth/surroundings of a hole, not through-hole creation. Reaming only sizes an existing hole. Tapping forms threads, not the basic hole. Common Pitfalls: Assuming trepanning equals hole saw use only; trepanning can also be performed on lathes and milling machines with dedicated tools and coolant arrangements. Final Answer: Producing a hole by removing material along the circumference using a hollow cutting tool

Question 11

Turning on a lathe: maintaining constant cutting speed  In a turning operation on a lathe, as machining proceeds the workpiece diameter reduces. To keep the cutting speed (surface speed at the tool–work interface) approximately constant, how should …

Accepted Answer

Introduction / Context: In machining, tool life, surface finish, and productivity depend strongly on cutting speed at the tool–work interface. In turning, the instantaneous cutting speed is set by both spindle revolutions per minute (RPM) and the current workpiece diameter. Given Data / Assumptions: Cylindrical turning on a lathe. Cutting speed V is the target value recommended for the tool–work material pair. Diameter D decreases during the pass as material is removed. Concept / Approach: The relationship between cutting speed V, spindle speed N, and diameter D is V = pi * D * N / 1000 (for V in m/min, D in mm, N in rev/min). To maintain V constant while D decreases, N must increase proportionally. Step-by-Step Solution: Start with V_target for the material and tool.Use V = pi * D * N / 1000 to find N = (1000 * V) / (pi * D).As D reduces during machining, the denominator decreases, so N must rise to keep V constant. Verification / Alternative check: Example: If V = 120 m/min, D from 60 mm to 40 mm. Initially N ≈ (1000120)/(pi60) ≈ 637 RPM; later N ≈ (1000120)/(pi40) ≈ 955 RPM. RPM increases as expected. Why Other Options Are Wrong: Decrease/keep constant: both reduce surface speed as D shrinks, risking rubbing and poor finish. Alternating or back-gear suggestions do not control V systematically and are unrelated to D changes. Common Pitfalls: Confusing feed rate with cutting speed; forgetting to adjust RPM on manual lathes during deep roughing cuts. Final Answer: Increase the spindle speed

Question 12

Single-point cutting tool nomenclature  The angle formed between the tool face and a plane parallel to the tool base (reference plane) is called what?

Accepted Answer

Introduction / Context: Tool geometry terms—rake, clearance, and edge angles—govern chip formation, cutting forces, heat generation, and tool life. Accurate definitions are essential for setup and troubleshooting. Given Data / Assumptions: Orthogonal tool geometry terminology per standard reference planes. Plane parallel to base is the reference (rake) plane. Concept / Approach: The rake angle is the inclination of the tool face relative to the reference plane. Positive rake promotes easier shearing and lower forces; negative rake strengthens the edge for hard materials. Clearance (relief) is the angle between the flank and the work surface to prevent rubbing. Step-by-Step Solution: Identify the surfaces: “face of the tool” versus “plane parallel to the base.”By definition, this is the rake angle that controls chip flow direction and shear deformation. Verification / Alternative check: Standard tool signature formats (e.g., ASA, ORS) list rake angles with respect to reference planes parallel to the base. Why Other Options Are Wrong: Cutting angle/lip angle refer to resultant included angles at the cutting edge, not the face-to-base relation. Clearance angle is between flank and work surface. Approach angle relates the cutting edge to feed direction. Common Pitfalls: Mixing rake and clearance; forgetting that rake deals with chip flow while clearance prevents rubbing. Final Answer: Rake angle

Question 13

Twist drill geometry for soft materials  For drilling softer materials (e.g., aluminium, brass, plastics), how should the drill point angle be chosen relative to the common 118° point used for steels?

Accepted Answer

Introduction / Context: Drill point angle affects chisel edge length, thrust force, centering, and chip evacuation. Different materials call for different geometry to minimize burrs and improve finish. Given Data / Assumptions: “Softer” materials imply lower strength and often gummy behavior. Standard steel drills commonly use about 118° point angle. Concept / Approach: Reducing the point angle (making it sharper) decreases the chisel edge length and cutting load, improving penetration and reducing thrust for soft metals and plastics. It also promotes more efficient shearing at the lips. Step-by-Step Solution: Target: Lower thrust and cleaner entry in soft materials.Choose a point angle less than 118° (e.g., 90–110° depending on material) to sharpen the point and ease cutting. Verification / Alternative check: Machining handbooks list smaller point angles for soft, non-ferrous materials; harder alloys often use 130–140° to strengthen the point. Why Other Options Are Wrong: =118° is acceptable but not optimal for many soft materials. >118° suits harder materials; increases thrust on soft stocks. “Any of these” ignores material-specific optimization. “Exactly 135° only” is too blunt for many soft materials. Common Pitfalls: Using the same drill geometry for all materials; ignoring lip clearance and helix angle which also affect performance. Final Answer: Less than 118° (sharper point)

Question 14

Effect of side cutting edge (approach) angle  If the side cutting edge angle of a single-point tool is made significantly larger than about 15°, what is the most likely consequence?

Accepted Answer

Introduction / Context: The side cutting edge angle (approach angle) influences chip width and thickness, radial/axial force components, and tool edge strength. Choosing it poorly can cause chipping or chatter. Given Data / Assumptions: Turning with a single-point tool on ductile metals. Other angles, feeds, and depths of cut are moderate. Concept / Approach: Increasing the side cutting edge angle spreads the cut over a wider edge, reducing chip thickness and often improving finish. However, beyond a typical range (about 10–15° for general work), the long, exposed cutting edge becomes weaker, susceptible to chipping at the nose and along the edge, especially under interrupted cuts or hard spots. Step-by-Step Solution: As the side cutting edge angle increases, chip thickness reduces and radial force can rise.Edge strength decreases because a longer edge is engaged; localized load at the nose increases risk of micro-chipping.Result: accelerated wear and chipping → reduced tool life. Verification / Alternative check: Tool-life tests show that very large approach angles can trigger chatter and edge breakdown, outweighing any finish gain. Why Other Options Are Wrong: “Increases tool life” conflicts with edge-strength considerations at large angles. “Slightly decreases but improves finish” can occur at moderate angles, not when it is significantly larger than 15°. “Excessive stress regardless of feed” is too absolute; process parameters matter. “No effect” is incorrect; approach angle affects force decomposition and chip load. Common Pitfalls: Assuming “more angle always better finish” without considering tool strength and chatter limits. Final Answer: Produces edge chipping and decreases tool life

Question 15

Centreless grinding: factors affecting axial feed rate  Which parameters primarily influence the axial feed rate of the workpiece in centreless through-feed grinding?

Accepted Answer

Introduction / Context: In centreless through-feed grinding, work does not rely on centers or chucks. The regulating wheel imparts rotation and axial feed, while the grinding wheel removes material. Understanding what drives feed rate is essential for productivity and roundness control. Given Data / Assumptions: Through-feed setup with a work-rest blade. Steady-state grinding with properly dressed wheels. Concept / Approach: Axial feed rate in through-feed depends on the regulating wheel kinematics and geometry. The axial component of the regulating wheel’s surface velocity, created by tilting its axis by a small angle relative to the grinding wheel axis, pushes the work along. Step-by-Step Solution: Diameter of regulating wheel affects surface speed for a given RPM.Regulating wheel speed directly sets tangential velocity and thus axial component.Inclination angle determines the proportion of tangential speed resolved in the work-axis direction → higher angle, higher feed. Verification / Alternative check: Feed per minute ≈ V_reg * sin(theta), where V_reg is regulating wheel peripheral speed and theta is the inclination angle; diameter influences V_reg for fixed RPM. Why Other Options Are Wrong: Focusing only on grain size ignores the kinematic origin of feed; grain size affects finish and forces, not the primary feed mechanism. Common Pitfalls: Confusing grinding wheel speed with feed control; in centreless grinding, the regulating wheel governs feed and rotation. Final Answer: All of the above

Question 16

Selecting cutting speed with HSS tools  When machining with a high-speed steel (HSS) tool, for which of the following materials is the recommended cutting speed typically the lowest?

Accepted Answer

Introduction / Context: Choosing cutting speed depends on tool material and work material. HSS has lower hot hardness than carbides, so speeds must be conservative, especially on abrasive or hard materials. Given Data / Assumptions: Conventional dry or lightly lubricated turning/milling. Standard HSS grades and average setups. Concept / Approach: Cast irons (especially grey cast iron) contain free graphite and hard carbides that abrade edges and generate discontinuous chips. To preserve tool life with HSS, lower cutting speeds are used than for ductile, free-cutting nonferrous metals like aluminium or brass. Step-by-Step Solution: Rank typical speeds (HSS): Aluminium >> Brass > Mild steel > Cast iron (lowest).Therefore, select cast iron for minimum recommended cutting speed among listed choices. Verification / Alternative check: Machining data tables confirm that HSS speeds for aluminium can be several times those for grey cast iron; brass also allows higher speeds than steels. Why Other Options Are Wrong: Mild steel, brass, aluminium permit higher speeds with HSS due to better machinability and less abrasion. Common Pitfalls: Confusing feed or depth of cut with cutting speed; underestimating abrasive wear in cast iron. Final Answer: Cast iron

Question 17

Chip formation and built-up edge (BUE)  Under which cutting conditions are continuous chips with a built-up edge most likely to form during metal cutting?

Accepted Answer

Introduction / Context: Built-up edge (BUE) is a transient layer of work material that adheres to the tool rake face and cutting edge, altering geometry and degrading finish. Controlling BUE is key to consistent surface quality. Given Data / Assumptions: Ductile materials, moderate to low cutting temperatures. Ordinary tool surfaces without special coatings or lubrication. Concept / Approach: BUE tends to form when friction and adhesion dominate, which occurs at low cutting speeds (insufficient temperature to stabilize a shear zone and promote clean separation) and with small rake angles (higher normal pressure on the rake face). This increases sticking and promotes accumulation of welded material at the edge. Step-by-Step Solution: Low speed → lower shear-zone temperature → higher adhesion and friction.Small rake angle → larger negative normal force on rake face → more sticking.Result: continuous chip with BUE is likely. Verification / Alternative check: Raising cutting speed, using sharper (larger positive rake) tools, or adding cutting fluids reduces BUE occurrence, which aligns with shop practice. Why Other Options Are Wrong: Large rake or high speeds reduce contact length and adhesion, mitigating BUE. Very high speed with sharp rake and coolant typically yields continuous chips without BUE or even discontinuous chips depending on material. Common Pitfalls: Confusing BUE with serrated chips at very high speeds; ignoring tool coatings that also suppress BUE. Final Answer: Low cutting speed and small rake angle

Question 18

Indexing on a milling machine  Which indexing method enables obtaining virtually any number of equal divisions on a workpiece gear/blank, beyond those available with simple plates alone?

Accepted Answer

Introduction / Context: Indexing heads allow precise angular divisions for gear cutting and fluting. Some tooth counts cannot be achieved with fixed hole circles and simple ratios. Given Data / Assumptions: Universal dividing head with change gears available. Objective: realize arbitrary tooth numbers. Concept / Approach: Direct indexing uses a fixed plate, limited to specific divisions (e.g., 24). Simple indexing uses one index plate and crank, limited by hole counts. Compound indexing extends choices via two-hole-circle operations but still finite. Differential indexing gears the index plate to the spindle, creating a small additional rotation that effectively produces almost any division. Step-by-Step Solution: Identify tooth count not available on existing hole circles.Set change gears to create the necessary differential motion.Crank turns while plate slowly rotates, yielding the required division. Verification / Alternative check: Shop texts list that differential indexing can generate prime numbers like 73 teeth not obtainable by simple plates. Why Other Options Are Wrong: Direct/simple indexing limited by plate holes. Compound indexing expands options but still constrained. Hand rotary tables lack precise equal divisions without verniers/gearing. Common Pitfalls: Incorrect gear train setup causing cumulative error; forgetting to lock the plate properly in non-differential modes. Final Answer: Differential indexing

Question 19

Relief (clearance) angle for soft materials  In machining soft materials, is it correct practice to use a tool with a negative relief (clearance) angle?

Accepted Answer

Introduction / Context: The relief (clearance) angle prevents the tool flank from rubbing the freshly cut surface. Its selection depends on work material and tool material, affecting heat, wear, and surface integrity. Given Data / Assumptions: Soft, ductile materials (e.g., aluminum, copper, plastics). Conventional single-point tools or drills. Concept / Approach: A negative relief angle would cause the flank to press against the work, dramatically increasing friction and heat, leading to rubbing, built-up edge, and poor finish. For soft materials, positive rake and adequate positive relief are preferred to reduce cutting forces and avoid smearing. Step-by-Step Solution: Recognize that relief angle must be positive for clearance.For soft materials, use larger positive rake and suitable positive relief to minimize rubbing and adhesion.Therefore, the statement that negative relief is used is incorrect. Verification / Alternative check: Tool geometry charts show relief angles typically 6–12° (or higher for very soft materials); negative relief is reserved for special cases on hard/brittle materials with negative rake, not negative relief. Why Other Options Are Wrong: Limiting to specific alloys or inserts does not justify negative relief; modern carbides sometimes use negative rake, but relief remains positive. High cutting speeds do not change the need for flank clearance. Common Pitfalls: Confusing rake (which can be negative for strength) with relief (which must remain positive to avoid rubbing). Final Answer: Incorrect

Question 20

Producing tapers by centreless grinding  Which centreless grinding method is commonly used to produce a tapered workpiece profile?

Accepted Answer

Introduction / Context: Centreless grinding has three principal modes: through-feed, infeed (plunge), and end-feed. Each suits different geometries such as straight cylinders, shoulders, and tapers. Given Data / Assumptions: Standard centreless setup with regulating wheel, grinding wheel, and work-rest blade. Objective is a continuous taper over length, not a short chamfer or shoulder. Concept / Approach: Through-feed keeps the work moving axially at a constant rate and is ideal for straight cylindrical parts; it cannot generate an intentional taper unless the machine is set with a tapered blade or special alignment, which is not typical. Infeed (plunge) is used for shouldered/formed parts where grinding occurs without axial feed. End-feed feeds the work axially until it stops (often against a stop) while the regulating wheel axis is set at a slight angle or the work-rest arrangement is adjusted to produce a taper along the part. Step-by-Step Solution: Select end-feed mode for parts requiring a taper over length.Set regulating wheel angle and/or work-rest blade height to achieve desired taper per unit length.Grind while feeding the work until the stop is reached, forming the taper. Verification / Alternative check: Machine manuals specify end-feed for cones/tapers; infeed is for profiles/shoulders, through-feed for straight bars and pins. Why Other Options Are Wrong: Through-feed: produces straight parallel diameters by default. Infeed: used for localized features and forms, not a continuous taper length. “Any” or “form wheel only” misstate the typical centreless methods. Common Pitfalls: Confusing centre-type cylindrical grinding methods (where wheel dressing can create tapers) with centreless practices. Final Answer: End-feed grinding

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