Question 1

Grinding technology — specifying wheel hardness In abrasive machining, the hardness grade of a grinding wheel is designated by a letter of the alphabet rather than by conventional indentation scales. Which notation is used to specify grinding wheel …

Accepted Answer

Introduction / Context: Grinding wheels are engineered composites, and their ‘‘hardness’’ refers to the bond's holding power on the abrasive grains, not the intrinsic hardness of the abrasive mineral. This question checks whether you know the industry-standard way to specify wheel grade (hardness) versus material hardness scales used for metals and polymers. Given Data / Assumptions: The wheel is a bonded abrasive tool (e.g., aluminium oxide in vitrified or resin bond). Hardness here means bond retention strength, not grain hardness. Common material hardness scales (Brinell, Rockwell, Vickers) are for metallic indentation hardness. Concept / Approach: Wheel grade is standardized by letters from soft to hard (e.g., A = very soft through Z = very hard). This alpha code communicates how readily dull grains are released to self-sharpen. Indentation scales (Brinell, Rockwell, Vickers) measure resistance to plastic indentation and are unsuitable for a porous, multiphase wheel. Step-by-Step Solution: Identify what is being specified: grinding wheel grade (bond strength).Recall standard nomenclature: grades indicated by letters, often in the wheel specification string (e.g., 46A 60 K 7 V).Conclude that the correct notation is a letter of the alphabet, not a numeric indentation scale. Verification / Alternative check: Any wheel spec sheet lists the grain size, grade letter, structure number, and bond type; the grade position is always a letter that maps to soft/medium/hard categories. Why Other Options Are Wrong: Brinell, Rockwell, and Vickers measure metallic indentation hardness and cannot represent a bonded wheel’s grain-retention property. Shore hardness is primarily for elastomers and some plastics. Common Pitfalls: Confusing abrasive hardness (e.g., diamond harder than alumina) with wheel grade; a ‘‘hard’’ wheel can still contain a very hard abrasive but release it slowly, which affects grinding behavior. Final Answer: Letter of the alphabet

Question 2

Shaper mechanism — changing stroke length In a standard shaper with crank-and-slotted link (Whitworth) mechanism, how can the length of ram stroke be increased?

Accepted Answer

Introduction / Context: In shaping machines, the ram executes a reciprocating stroke produced by a crank-and-slotted link mechanism. Understanding which dimension governs stroke length is fundamental for setup and maintenance. Given Data / Assumptions: Whitworth quick-return mechanism is used. Stroke length is approximately twice the crank radius. Other link lengths mainly affect timing (quick return) rather than stroke magnitude. Concept / Approach: The ram stroke is generated by converting rotary motion of the bull gear to reciprocation via a crank pin and slotted link. The peak-to-peak displacement equals about 2 * crank radius. Therefore, increasing the crank radius directly increases stroke. Step-by-Step Solution: Relate stroke length S to crank radius r: S ≈ 2r.To increase S, increase r, which is the centre distance from bull gear centre to crank pin.Hence, select the option that increases this centre distance. Verification / Alternative check: Machine manuals show adjustable crank pins: moving the pin outward on the bull gear face plate increases stroke; moving inward decreases it. Why Other Options Are Wrong: Reducing the centre distance decreases stroke; modifying slotted link/arm length changes velocity characteristics, not stroke magnitude; clapper box angle affects tool relief on return, not stroke length. Common Pitfalls: Confusing quick-return ratio adjustments with stroke length; they are related but controlled by different geometric parameters. Final Answer: Increase the centre distance between the bull gear centre and the crank pin (i.e., increase crank radius)

Question 3

Broaching fundamentals — function of rear teeth What do the rear (trailing) teeth of a broach primarily do during a pass?

Accepted Answer

Introduction / Context: A broach is a multi-tooth tool with progressively increasing tooth height. Its tooth arrangement splits work between roughing, semi-finishing, finishing, and sometimes burnishing lands. Recognizing the role of each section is key to process design and surface integrity control. Given Data / Assumptions: Standard pull-type internal broach with roughing teeth, finishing teeth, and burnishing (sizing) lands at the rear. Feed per tooth (rise-per-tooth) is front-loaded; burnishing lands have zero rise. Concept / Approach: Roughing teeth remove the bulk allowance. Finishing teeth remove a small, uniform allowance to achieve size and reduce tool load. The last ‘‘rear’’ teeth are burnishing lands with no additional rise; they plastically smooth asperities and size the hole by ironing rather than cutting, hence removing essentially no metal. Step-by-Step Solution: Identify tooth sequence: rough → finish → burnish.Note burnish lands have zero chip load (rise-per-tooth = 0).Therefore, rear teeth do not cut; they size and smooth, removing no measurable metal. Verification / Alternative check: Surface roughness after burnishing typically improves by 1–2 grades without corresponding chip formation; chips end before the burnish zone. Why Other Options Are Wrong: Burnishing is a plastic deformation/ironing action, not metal removal; finishing teeth do remove minimum metal, but they are not the very rear burnishing lands; roughing removal is at the front. Common Pitfalls: Using the term ‘‘rear teeth’’ for finishing teeth; in many texts, ‘‘rear’’ specifically refers to the final, zero-rise burnishing lands. Final Answer: Remove no metal at all

Question 4

Thread grinding — recommended work (job) speed Typical workpiece peripheral speed selected for thread grinding operations is in the range of:

Accepted Answer

Introduction / Context: Thread grinding requires accurate lead control and crest-root definition. Because the form must be generated precisely by the wheel, job (workpiece) speed is kept low to maintain profile fidelity and minimize dynamic errors. Given Data / Assumptions: Cylindrical thread grinding with a single- or multi-rib form wheel. High wheel speeds; careful synchronization for lead. Goal is accuracy and fine finish, not stock removal rate. Concept / Approach: Lower work peripheral speeds reduce chatter risk and thermal distortion while allowing finer control of the helical path relative to wheel form. Typical practice limits work speed to only a few metres per minute, while the grinding wheel runs at very high surface speeds. Step-by-Step Solution: Recognize the need for positional accuracy → choose conservative work speed.Typical data tables specify work speeds approximately 1–3 m/min for thread grinding.Therefore, select 1 to 3 m/min. Verification / Alternative check: Machine builders’ charts and shop handbooks list low work speeds for thread grinding compared with plain cylindrical grinding, which often allows higher job speeds. Why Other Options Are Wrong: Speeds above ~5 m/min increase risk of profile errors and chatter; 10–20 m/min are more typical of other grinding operations, not precision thread grinding. Common Pitfalls: Confusing wheel speed (very high) with workpiece speed (low); mixing recommendations for traverse cylindrical grinding with form grinding of threads. Final Answer: 1 to 3 m/min

Question 5

Machinability criterion — key geometric indicator Which geometric parameter in metal cutting is often used as a criterion for machinability comparisons?

Accepted Answer

Introduction / Context: Machinability refers to how easily a material can be machined to an acceptable surface finish, dimensional accuracy, and tool life. Several indicators exist, but one geometric parameter directly connected to chip formation and cutting forces is frequently used: the shear angle. Given Data / Assumptions: Orthogonal cutting model for analysis. Chip thickness ratio and rake angle are measurable. Higher shear angle generally implies thinner shear plane and lower cutting force. Concept / Approach: From the orthogonal cutting model, shear angle phi relates to chip thickness ratio r and rake angle alpha. A larger phi reduces shear plane area, lowering energy per unit volume removed and enabling smoother chip flow. Materials exhibiting larger shear angles at comparable conditions typically show better machinability. Step-by-Step Solution: Link machinability to chip formation efficiency.Recognize that higher shear angle correlates with lower cutting forces and temperatures.Therefore, shear angle serves as a practical comparative criterion. Verification / Alternative check: Empirical tests show materials adding free-machining additives (e.g., S, Pb) exhibit increased shear angle and improved chip breakage, aligning with easier machining. Why Other Options Are Wrong: Cutting speed and feed rate are process settings, not intrinsic geometric indicators; tool nose radius and rake angle are tool geometry choices rather than material response metrics. Common Pitfalls: Assuming a single scalar defines machinability completely; in practice, machinability is multi-factor (surface finish, tool life, power, chip control). Final Answer: Shear angle

Question 6

Tool life and speed — Taylor’s law insight State the relationship: as cutting speed increases, what happens to tool life (all else equal)?

Accepted Answer

Introduction / Context: Taylor’s tool life equation captures the dominant influence of cutting speed on tool life. Recognizing this trend is essential for selecting economical cutting parameters and planning tool-change intervals. Given Data / Assumptions: Taylor’s equation in basic form: V * T^n = C (feed and depth constant). Workpiece–tool material pair is fixed. Failure criterion for tool wear is predefined (e.g., flank wear land). Concept / Approach: According to V * T^n = C, for a given tooling/workpiece combination, increasing speed V requires a compensating decrease in tool life T to maintain the constant C. Higher speed increases cutting temperature and wear rate (diffusion, abrasion, adhesion), thereby shortening life. Step-by-Step Solution: Start with V * T^n = C.If V increases ⇒ T must decrease because n > 0.Thus, tool life decreases as speed increases. Verification / Alternative check: Shop trials plotting log V versus log T give a straight line with negative slope (−1/n), confirming inverse relation. Why Other Options Are Wrong: Options claiming increased or constant life ignore thermal and wear mechanisms that accelerate with speed; non-monotonic behavior requires atypical conditions not implied here. Common Pitfalls: Changing feed/depth simultaneously can mask the speed effect; always compare at constant feed and depth. Final Answer: Yes — tool life decreases with higher cutting speed

Question 7

Tool wear mechanisms — where is crater wear most predominant? Identify the tool material that most commonly exhibits crater wear on the rake face under conventional cutting conditions.

Accepted Answer

Introduction / Context: Tool wear appears mainly as flank wear (clearance face) and crater wear (rake face). Which mechanism dominates depends on tool material, cutting temperature, and chemistry. Recognizing where crater wear is prevalent helps with material and coating selection. Given Data / Assumptions: Conventional machining of steels at moderate-to-high speeds. Uncoated baseline tool materials considered. Crater wear forms via diffusion/adhesion at high rake-face temperatures. Concept / Approach: HSS operates at lower hot hardness than carbides and ceramics; its rake face reaches temperatures that promote diffusion between chip and tool, forming a crater behind the cutting edge. Carbides and ceramics maintain higher hot hardness and better crater resistance; they more often show flank wear limits. Carbon tool steels are used at very low speeds and generally fail by softening; ceramics and diamonds resist crater but can suffer notch or brittle chipping. Step-by-Step Solution: Compare hot hardness and chemical stability among tool materials.Note crater wear prevalence when tool–chip interface temperature is high and tool hot hardness is modest (HSS).Conclude HSS tools are most prone to crater wear in typical conditions. Verification / Alternative check: Metallographic examination of worn HSS tools frequently shows a distinct crater zone on the rake face, whereas carbides show slower crater development but steady flank wear. Why Other Options Are Wrong: Carbides and ceramics have superior crater resistance; carbon tool steels are seldom used at speeds that create distinct crater wear; PCD resists crater under most metal cutting but is used for nonferrous materials. Common Pitfalls: Assuming the hardest material always avoids all rake-face wear; even hard materials can crater at extreme speeds, but relative tendency is highest for HSS. Final Answer: High-speed steel (HSS) tools

Question 8

Workholding on a shaper — table slot form The top and sides of a shaper table are machined with which standard slot type for clamping and fixtures?

Accepted Answer

Introduction / Context: Secure workholding is critical on shaping machines due to intermittent cutting and reversing forces. Standardized slots enable flexible clamping with bolts, nuts, and step blocks. Knowing the slot form used on shaper tables is basic shop knowledge. Given Data / Assumptions: Conventional horizontal shaper with box-type table. Need to restrain fixtures against uplift and lateral loads. Compatibility with common clamping kits. Concept / Approach: T-slots allow the bolt head or T-nut to slide under the table surface within a re-entrant feature, providing a positive mechanical interlock that resists pull-out. Straight or L-shaped open slots lack this undercut and are not standard for machine tables. Step-by-Step Solution: Identify standard machine tool tables (milling, shaper, planer) → T-slots.T-slots accept T-nuts/bolts to clamp vises, angle plates, and work directly.Therefore, choose T-type slots. Verification / Alternative check: Any shaper/milling table parts diagram highlights nominal width and pitch of T-slots for accessory compatibility. Why Other Options Are Wrong: L- or I-type open slots fail to capture bolt heads; dovetail slots are used for slides/ways, not general clamping on table surfaces. Common Pitfalls: Confusing dovetail slideways (guide geometry) with table clamping slots; they serve different purposes. Final Answer: T-type slots

Question 9

Lathe capacity terminology — swing over bed The swing diameter over the bed of a lathe is how many times the centre height (centre above bed)?

Accepted Answer

Introduction / Context: Lathe capacity is commonly specified by ‘‘swing over bed’’ and ‘‘distance between centres.’’ Understanding the geometric relationship between swing and centre height is essential for checking whether a workpiece diameter can clear the bed. Given Data / Assumptions: Centre height H is the vertical distance from bed top to spindle centreline. Swing over bed is the maximum work diameter that can rotate without hitting the bed. Concept / Approach: If the spindle centre is H above the bed, a circle of radius H can rotate without interference, so the maximum diameter equals 2H. Hence, swing over bed equals twice the centre height. Step-by-Step Solution: Let centre height = H.Clearance radius = H ⇒ maximum diameter = 2H.Therefore, swing over bed = 2 × centre height. Verification / Alternative check: Machine nameplates often list, e.g., ‘‘Swing over bed 400 mm’’ which implies centre height of 200 mm. Why Other Options Are Wrong: Other multiples do not match the simple geometry of radius versus diameter; one-half would correspond to radius, not diameter. Common Pitfalls: Confusing ‘‘swing over carriage’’ (smaller) with ‘‘swing over bed.’’ Accessories reduce practical swing further. Final Answer: Twice the centre height

Question 10

Selecting abrasives — high tensile strength materials Which abrasive is generally recommended for grinding steels and other high tensile strength materials?

Accepted Answer

Introduction / Context: Correct abrasive selection improves grinding performance, wheel life, and surface integrity. The choice depends strongly on the work material’s mechanical and chemical properties. Given Data / Assumptions: Target work materials: carbon/alloy steels with high tensile strength. Conventional vitrified or resin-bonded wheels are considered. Goal: efficient cutting without excessive wheel wear or loading. Concept / Approach: Aluminium oxide is tough and fracture-resistant, making it suitable for ferrous alloys with high tensile strength. Silicon carbide is sharper but more brittle; it excels on low-tensile, hard-brittle or nonferrous materials (cast iron, carbide, glass). Diamond is chemically reactive with iron at high temperatures, causing rapid wear; it is reserved for carbides, ceramics, and nonferrous composites. Natural stones like sandstone/garnet are obsolete for precision grinding. Step-by-Step Solution: Match abrasive toughness to ductile, high-tensile steels → choose Al2O3.Avoid SiC for steels where micro-chipping and rapid dulling occur.Exclude diamond for ferrous grinding due to graphitization/chemical wear. Verification / Alternative check: Wheel specification guides list Al2O3 (A) wheels for steel; SiC (C) wheels for cast iron, brass, aluminium, and carbides. Why Other Options Are Wrong: Silicon carbide is ideal for low-tensile or hard-brittle materials; sandstone/garnet are not used for modern precision grinding; diamond reacts with iron and is uneconomical for steels. Common Pitfalls: Choosing ‘‘harder’’ abrasives blindly; toughest is not always best—compatibility with work material and grinding heat is crucial. Final Answer: Aluminium oxide (Al2O3)

Question 11

Grinding practice – reducing glazing on a wheel: In production grinding, a wheel may “glaze” (dulled abrasive tips, shiny surface). Which change most effectively reduces glazing and restores cutting action?

Accepted Answer

Introduction / Context: Glazing of a grinding wheel occurs when abrasive grains become dull but are not shed by the bond. The wheel surface turns shiny, chip space clogs, forces rise, temperature increases, and the part may burn. This question tests corrective actions rooted in grinding wheel selection and cutting speed control. Given Data / Assumptions: Wheel has glazed (dull cutting points, high rubbing). Work material and coolant remain unchanged. Machine is capable of adjusting wheel grade and speed (or allowing a wheel change). Concept / Approach: Abrasive self-sharpening relies on timely grain fracture or pull-out. If the wheel is too hard or the peripheral speed is too high, dull grains are held too strongly and continue rubbing. Selecting a softer grade promotes grain release; lowering wheel speed reduces rubbing and encourages renewed cutting. Step-by-Step Solution: Identify symptom: shiny wheel face, higher power, poor surface → glazing.Root cause: wheel too hard for the job or speed too high, so dull grains cannot dislodge.Corrective actions: choose softer grade to enhance self-sharpening; reduce wheel speed to reduce rubbing and heat.Supplement: increase infeed or dress more aggressively to open the wheel structure. Verification / Alternative check: After switching to a softer wheel or reducing speed, the specific grinding energy drops, sparks become more active, and the surface finish improves without burn—evidence of restored cutting. Why Other Options Are Wrong: Harder wheel/increase speed: aggravates glazing. Harder wheel/decrease speed: still retains dull grains too long. Softer wheel/increase speed: higher speed promotes rubbing; mixed outcome. Dress less frequently: opposite of what is needed; dressing opens the wheel. Common Pitfalls: Confusing glazing with loading; loading is chip packing, fixed by dressing and coolant filtration, not merely wheel grade. Final Answer: Using a softer wheel or by decreasing the wheel speed

Question 12

Machining fundamentals – what is threading? Identify the process that correctly defines the threading operation on a lathe or similar machine.

Accepted Answer

Introduction / Context: Threading is a core turning operation used to produce fastening features. Confusing threading with related hole-finishing operations (reaming, counterboring) leads to incorrect process planning and tool selection. Given Data / Assumptions: Conventional single-point threading on a lathe is considered. External screw threads on shafts, studs, or bolts. Standard feeds synchronized with spindle via a leadscrew/gearbox. Concept / Approach: External threading removes material in a helical path to form crests, roots, and flanks according to thread standards (e.g., metric, unified). The tool follows a lead equal to pitch per revolution, generating the helix. Step-by-Step Solution: Classify operations: reaming sizes holes; counterboring squares a shoulder; trepanning bores a ring.Threading requires a single-point tool with included angle (e.g., 60 degrees for metric/unified).Set gearbox to thread pitch; align tool; make successive passes to full depth.The final result is a helical groove profile on the external surface. Verification / Alternative check: Measurement with thread pitch gauge and thread micrometer confirms the helix parameters match the target standard. Why Other Options Are Wrong: Smoothing/squaring a hole mouth describes counterboring/chamfering, not threading. Sizing/finishing a hole is reaming. Removing metal along a hollow tool circumference is trepanning or core drilling. Press fitting is an assembly method, unrelated to thread cutting. Common Pitfalls: Mixing tapping (internal threading) with reaming; assuming multi-point dies are mandatory—single-point tools are common for flexible thread generation. Final Answer: Cutting helical grooves on the external cylindrical surface

Question 13

Milling nomenclature: “Down milling” is commonly referred to by which other name in manufacturing practice?

Accepted Answer

Introduction / Context: Understanding climb (down) versus conventional (up) milling is essential for choosing feed direction, chip thickness progression, surface finish, tool life, and fixture design. The question tests terminology and associated process awareness. Given Data / Assumptions: Peripheral milling on a horizontal or vertical machine. Workpiece feed direction either with or against the cutter rotation at the contact point. Proper machine backlash control assumed for climb milling. Concept / Approach: In climb (down) milling, the cutter rotation and table feed are in the same direction at the engagement zone, so chip thickness starts at maximum and reduces to zero at exit. This tends to push the work into the table, improves surface finish, and reduces rubbing. Conventional (up) milling is opposite. Step-by-Step Solution: Relate “down” to the direction of the resultant force—pushing down on the work.Recognize industry synonym: down milling ≡ climb milling.Note machine requirements: minimal backlash and rigid fixturing are needed to prevent pull-in.Benefits include lower cutting temperature and better finishes for many materials. Verification / Alternative check: Chip thickness progression diagrams show maximum-to-zero in climb versus zero-to-maximum in conventional; this confirms the naming convention. Why Other Options Are Wrong: End and face milling describe tool geometry and operation type, not feed direction; conventional milling is the opposite of down (climb) milling; slot milling is a specific feature operation. Common Pitfalls: Attempting climb milling on worn machines with backlash—this can pull the table suddenly and damage the job or tool. Final Answer: Climb milling

Question 14

Capabilities of milling cutters: Which set best represents what can be performed on a milling machine using appropriate cutters and setups?

Accepted Answer

Introduction / Context: Milling machines are versatile. With the correct cutters, arbors, and indexing/gear trains or CNC interpolation, they can produce a wide range of features beyond simple slots and faces. Given Data / Assumptions: Availability of standard and form cutters (end mills, side-and-face, woodruff, involute gear cutters). Thread milling possible using single-form cutters or multi-tooth thread mills with synchronized motion. Dividing head (indexing) or CNC control for gear cutting and helical threads. Concept / Approach: Keyways are cut with end mills or woodruff cutters; external threads can be milled helically; spur gears are cut with involute gear cutters using indexing. The same platform supports complex profiles by coordinated toolpaths. Step-by-Step Solution: Keyways: center cutting end mill to required width and depth; maintain alignment.External thread milling: synchronize feed to create the helix lead; choose appropriate pitch-form tool.Spur gear cutting: mount dividing head; select involute cutter matching module/DP and tooth number.Verify dimensions with gauges and micrometers. Verification / Alternative check: Finished parts are checked using keyway gauges, thread plug/ring gauges, and gear tooth verniers or span measurements confirming feasibility on milling machines. Why Other Options Are Wrong: Each single-operation choice understates milling capability; claiming none is incorrect because all listed operations are routine with proper setup. Common Pitfalls: Poor fixturing or ignoring indexing accuracy during gear cutting; neglecting cutter selection per module or pitch. Final Answer: All of these (keyways, external threads by thread milling, and spur gear teeth)

Question 15

Single-point cutting tools – definition check: The back rake angle is the angle by which the tool face is inclined towards the back (away from the cutting edge) in the longitudinal plane. Is this statement correct?

Accepted Answer

Introduction / Context: Tool geometry controls chip flow, cutting forces, heat, and surface finish. Back rake angle and side rake angle are fundamental rake parameters for single-point tools used in turning and shaping. Given Data / Assumptions: ASA/ORS style definitions for tool angles. Reference planes: base reference and longitudinal plane through the cutting edge. Right-hand tool example for discussion. Concept / Approach: Back rake angle is measured in the plane that is parallel to the tool shank’s longitudinal axis and passes through the cutting edge. A positive back rake means the face slopes away from the cutting edge toward the shank (“back”), guiding chip flow and lowering cutting force. Negative rake strengthens the edge for hard materials. Step-by-Step Solution: Identify the tool face and cutting edge geometry.Back rake: inclination of face from a normal to the base measured in the longitudinal plane—slope toward the tool’s rear.Positive back rake enhances shear action and chip evacuation; negative rake increases edge strength and compressive loading.Therefore the quoted definition aligns with standard nomenclature. Verification / Alternative check: Compare with tool geometry handbooks: back rake (longitudinal) versus side rake (transverse); sketches confirm the inclination direction. Why Other Options Are Wrong: Limiting validity to specific tool types or feed rates is incorrect; back rake is a geometric definition independent of feed and applies to all single-point tools. Common Pitfalls: Confusing back rake with clearance angles; clearance prevents rubbing of the flank, while rake controls chip flow and cutting action. Final Answer: Agree

Question 16

Chip control in metal cutting: In machining of metals, chips tend to break primarily because of which material or process characteristic?

Accepted Answer

Introduction / Context: Chip formation governs surface finish, tool life, and safety. Chips may be continuous, segmented, or discontinuous. Knowing why chips break helps in selecting cutting parameters, chip breakers, and tool materials. Given Data / Assumptions: Orthogonal cutting with a sharp tool. Work materials showing strain hardening (work hardening) under plastic deformation. Moderate cutting speeds where thermal softening does not dominate. Concept / Approach: As the chip forms and flows up the rake face, it undergoes severe plastic strain and cyclic bending over the tool/chip breaker. Many alloys exhibit strain hardening: their flow stress rises with plastic strain. This promotes periodic fracture of the chip root or along shear bands, creating segmented or broken chips. Step-by-Step Solution: During cutting, shear deformation raises dislocation density → material work hardens.A harder, less ductile chip segment bends over the tool/chip breaker and experiences tensile stresses.When local stress exceeds the work-hardened chip strength in bending, a crack initiates and the chip breaks.Proper chip breaker geometry accelerates this process to produce manageable chip lengths. Verification / Alternative check: Metallographic examination of chips shows shear localization bands and higher hardness compared to the parent material, confirming work hardening. Why Other Options Are Wrong: Toughness: Greater toughness resists fracture, encouraging continuous chips. Ductility: High ductility favors long continuous chips rather than breakage. Elasticity: Elastic effects are recovered and small; breakage is a plastic deformation/fracture phenomenon. Perfect lubrication: Reduces friction and heat; it does not inherently cause chip breakage. Common Pitfalls: Assuming brittle materials are the only source of chip breakage; even ductile alloys can produce segmented chips due to work hardening and thermal effects at certain speeds. Final Answer: Work hardening of the work material

Question 17

Heat partition in cutting – continuous chip: In continuous chip machining (good ductility, sharp tool, adequate speed), which sink removes the largest fraction of generated heat? Assess the statement “the tool takes the maximum heat.”

Accepted Answer

Introduction / Context: Metal cutting converts mechanical work into heat at the primary shear zone and the tool–chip interface. Where that heat goes affects temperatures, tool wear, and part integrity. This question checks understanding of heat partition in continuous chip formation. Given Data / Assumptions: Ductile material, sharp tool, typical production speeds. Continuous chip with or without a built-up edge. Coolant may or may not be applied but does not change the basic partition trend. Concept / Approach: In continuous chip cutting, most heat is carried away by the flowing chip because it is in intimate contact with the hot shear zone and departs the cutting region quickly with a relatively high mass flow and temperature rise. The tool and work each receive smaller portions of the heat. Step-by-Step Solution: Consider energy balance: Q_total = Q_chip + Q_tool + Q_work.Experiments show Q_chip is the dominant term for many ductile alloys at moderate to high speeds.Therefore the assertion “tool takes the maximum heat” is false; the chip is the primary heat carrier.Tool temperature control still matters because even a smaller fraction can raise tool-tip temperature significantly. Verification / Alternative check: Thermocouple tools and inverse heat conduction models consistently attribute the largest share of heat to the chip stream in continuous chip cutting. Why Other Options Are Wrong: Conditional statements about specific tool materials or hardened steels are special cases; the general rule under continuous chip conditions remains that the chip removes the most heat. Common Pitfalls: Confusing local peak temperature at the tool tip with total heat fraction; peak temperature can be high even if the fraction of heat to the tool is smaller than to the chip. Final Answer: No

Question 18

Drilling parameters – definition of depth of cut: In drilling operations, the standard definition of depth of cut is related to the drill diameter. Choose the correct relation.

Accepted Answer

Introduction / Context: Nomenclature in machining differs across processes. In turning, depth of cut is a radial measure; in drilling, the equivalent concept must be referenced to the drill geometry. Consistent definitions are necessary for calculating metal removal rate (MRR) and selecting conditions. Given Data / Assumptions: Standard twist drill creating a through or blind hole. Uniform feed per revolution and steady cutting. Neglecting point angle effects on instantaneous chip thickness. Concept / Approach: In drilling, two cutting lips remove material symmetrically. By analogy with turning, the depth of cut is taken as the radial engagement on one side, which equals half of the drill diameter D/2. This aligns MRR expressions with turning-style formats. Step-by-Step Solution: Let D = drill diameter.Define depth of cut t = D/2 (radial), width of cut is circumferential.Metal removal rate MRR = (π * D * f * N) * t for analogous forms; in drilling the common practical form is MRR = (π * D^2 / 4) * f * N.Both representations are consistent only when t = D/2. Verification / Alternative check: Comparing volumetric removal per revolution (hole cross-sectional area times feed) corroborates the D/2 definition. Why Other Options Are Wrong: Equal to D or double D are geometric exaggerations; one-fourth D does not match conventional definitions; claiming independence from diameter contradicts standardized machining terminology. Common Pitfalls: Mixing up feed (axial advance per revolution) with depth of cut (radial engagement); the drill point angle affects chip thickness locally but not the standard definition of depth of cut. Final Answer: One-half of the drill diameter

Question 19

Lathe headstock operation – effect of engaging the backgear: When the backgear train is engaged in a back-geared headstock, what happens to the spindle speed?

Accepted Answer

Introduction / Context: Back-geared headstocks provide low-speed, high-torque ranges for heavy turning, large diameters, or threading. Understanding their purpose is essential for safe setup and correct surface speed selection. Given Data / Assumptions: Conventional cone pulley with backgear train on an engine lathe. Backgear engagement inserts an extra gear reduction between the cone pulley and spindle. No change in motor speed. Concept / Approach: Engaging the backgear introduces a large reduction ratio. Speed decreases substantially, while torque at the spindle rises in proportion (neglecting losses). This enables cutting at the low surface speeds required for large diameters or tough materials. Step-by-Step Solution: Spindle speed N_spindle = N_motor * overall ratio.With backgear out: ratio close to 1 via the direct belt drive on the cone pulley.With backgear in: gear reduction R >> 1, so N_spindle = N_direct / R → much lower speed.Torque multiplication T ≈ T_direct * R (minus losses) allows heavy cuts. Verification / Alternative check: Nameplate speed charts on lathes show two ranges; the backgear range lists much lower rpm for the same pulley step. Why Other Options Are Wrong: Speed does not increase; it changes substantially, not “unchanged.” Direction does not reverse simply by engaging backgear; torque and speed are coupled by the reduction. Common Pitfalls: Engaging the backgear without disengaging the bull gear lock pin can lock the headstock and damage components. Final Answer: Agree – the spindle speed reduces considerably

Question 20

Tool materials – permissible cutting speed: High-speed steel (HSS) twist drills can be operated at approximately what multiple of the speed used for high-carbon steel (HCS) drills, for similar conditions?

Accepted Answer

Introduction / Context: Cutting speed limits are governed by hot hardness and wear resistance of tool materials. HSS retains hardness and edge strength at significantly higher temperatures than high-carbon steel (HCS), enabling higher practical surface speeds. Given Data / Assumptions: Comparable work material and coolant conditions. Similar tool geometry for HSS and HCS twist drills. Focus on order-of-magnitude speed capability, not an exact recommended value chart. Concept / Approach: HSS maintains cutting performance at elevated temperatures due to alloying (W, Mo, V, Cr, Co). Typical shop rules of thumb allow roughly twice the cutting speed (or more) with HSS compared to HCS while maintaining tool life. Step-by-Step Solution: Recognize property difference: HSS has higher red-hardness than HCS.Translate to permissible surface speed: V_HSS ≈ 2 * V_HCS for many steels and general drilling tasks.Set spindle speed from V = π * D * N / 1000 (for metric units) to achieve the higher surface speed with HSS.Monitor tool wear and adjust for specific materials and coatings. Verification / Alternative check: Machining handbooks and tool catalogs list higher recommended speeds for HSS than for HCS; the ratio commonly falls around two or more depending on alloy and coolant. Why Other Options Are Wrong: One-half or one-fourth contradict improved hot hardness; four times can be excessive under many shop conditions; “exactly the same” ignores material science differences. Common Pitfalls: Forgetting to also adjust feed, coolant, and peck cycles; exceeding machine power limits when increasing speed with large diameters. Final Answer: Double

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