18 Cutting Theory & Tooling Practice Questions & Answers

1. 1. During single-point metal cutting, how is the chip actually formed ahead of the cutting edge?

   • A.The work material is plastically deformed and shears along a shear plane ahead of the edge.✓ Answer
   • B.The cutting edge splits the material apart in front of it, much the way a wedge splits a log along its grain.
   • C.The heat of the cut melts a thin surface layer of metal, which the tool then wipes off the workpiece.
   • D.The tool abrades the surface, grinding away loose particles the way an abrasive wheel removes stock.

   Chip formation is plastic deformation, not splitting or melting: the tool compresses the material until it shears along a narrow shear zone (the zone of distortion) ahead of the edge. Nearly all the cutting energy is spent shearing that zone and rubbing the chip on the rake face, which is why the cut generates heat.

   Source: NIMS Machining Level I Standards (NIMS/ANSI 101-2001), KSAO 7.1 Cutting Theory — zone of distortion, cutting interface, chip formationReport a problem with this question

2. 2. A machinist turning gray cast iron sees the chips leave the tool as small separate segments instead of long coils. What does this indicate?

   • A.The tool has gone dull and must be reground, since a correctly sharpened tool always produces a long, continuous ribbon chip.
   • B.Normal discontinuous chip formation, because a brittle material such as gray cast iron fractures at the shear zone instead of flowing ahead of the tool.✓ Answer
   • C.The spindle speed has been set far above the safe range, and the chip is being torn apart by centrifugal force.
   • D.Coolant is not reaching the cut, so the chip is hardening and breaking before it has a chance to curl.

   Ductile materials such as low-carbon steel, aluminum and copper flow ahead of the tool and give continuous chips; brittle materials such as gray cast iron and bronze fracture in the shear zone and give discontinuous, segmented chips. That abrasive powdery chip is also why gray cast iron is commonly machined dry or with air rather than flood coolant.

   Source: NIMS Machining Level I Standards, KSAO 7.1 Cutting Theory — chip formation and machinability (continuous vs discontinuous chips)Report a problem with this question

3. 3. A soft, ductile low-carbon steel part is being turned at low speed. The finish is rough and torn and workpiece metal is found welded to the tool face. What is happening, and what is the correct remedy?

   • A.Crater wear is developing on the rake face; the correction is to change to a harder carbide grade and cut the feed rate roughly in half.
   • B.The relief angle is too large, so the unsupported edge is collapsing and smearing metal back onto the finished surface.
   • C.A built-up edge is forming; raise the cutting speed, increase rake angle, or improve the cutting fluid.✓ Answer
   • D.The work is strain hardening because the feed is too heavy; reduce the feed until the chip comes off as a fine powder.

   Built-up edge occurs when soft, gummy work material pressure-welds to the rake face at low cutting speed or with inadequate lubrication. The welded lump periodically breaks away and drags across the finished surface, so the cure is to get out of the BUE speed range (higher speed), reduce the tendency to weld (more positive rake), or improve lubrication.

   Source: NIMS Machining Level I Standards, KSAO 7.1 Cutting Theory — friction and cutting interface (built-up edge)Report a problem with this question

4. 4. In a normal metal-cutting operation with free chip flow, where does most of the heat generated at the cut go?

   • A.Into the workpiece, which absorbs most of the heat and must be allowed to cool between successive passes.
   • B.Into the cutting tool, which conducts the bulk of the heat away through the shank and into the toolholder.
   • C.Into the surrounding air and the machine structure, mainly by radiation from the exposed cutting zone.
   • D.Into the chip, which carries the large majority of the heat generated in the shear zone out of the cut as it leaves.✓ Answer

   Most of the energy of the cut becomes heat in the shear zone and at the chip/rake-face interface, and the chip carries the large majority of it away as it leaves. That is why a hot, discolored chip is normal while a hot workpiece or a hot tool signals that chip flow, speed, or coolant is wrong.

   Source: NIMS Machining Level I Standards, KSAO 7.1 Cutting Theory — heat, friction, cutting interfaceReport a problem with this question

5. 5. Wear that appears as a depression worn into the tool's rake face a short distance behind the cutting edge is called:

   • A.Crater wear, caused by the hot chip sliding across the rake face.✓ Answer
   • B.Flank wear, caused by rubbing between the relief face of the tool and the newly machined surface as the cut progresses.
   • C.Notch wear, caused by the abrasive hard skin or scale at the outer edge of the depth of cut biting into the tool.
   • D.Thermal cracking, caused by repeated heating and cooling cycles that open comb cracks across the cutting edge.

   Wear is classified by the surface it attacks: the rake face carries the chip, so friction and diffusion there hollow out a crater, while the relief (flank) face rubs the finished surface and wears a flat land. A deep crater thins the edge from behind and can cause sudden edge collapse, so it is watched as an end-of-tool-life indicator.

   Source: NIMS Machining Level I Standards, KSAO 7.1 Cutting Theory — tool wear modes (crater vs flank wear)Report a problem with this question

6. 6. A carbide insert keeps chipping at the cutting edge while taking an interrupted cut across a keywayed shaft. Which change is the most appropriate correction?

   • A.Switch to a ceramic insert and raise the cutting speed sharply, since ceramic is the hardest tool material and therefore resists every form of edge failure.
   • B.Select a tougher grade and a negative rake geometry so the edge is backed by more tool material and loaded in compression rather than bending.✓ Answer
   • C.Grind or index to a much larger positive rake so the sharper, keener edge slices through the interruption more easily.
   • D.Increase the relief angle so the flank clears the work and the edge no longer contacts the interrupted surface.

   Chipping is a mechanical shock failure, so the fix is toughness and edge support, not more hardness or a keener edge. Negative rake backs the edge with more tool material and loads it in compression, which brittle carbide withstands far better than the bending load imposed by a sharp positive-rake edge; ceramics are harder but more brittle still and are the worst choice for interrupted cuts.

   Source: NIMS Machining Level I Standards, KSAO 7.1/7.2 — shock, cutter geometry, and cutting tool material selectionReport a problem with this question

7. 7. Of cutting speed, feed rate and depth of cut, which variable has the greatest effect on tool life, and in what direction?

   • A.Depth of cut; increasing it shortens tool life more than any other variable, because it puts the greatest length of cutting edge into the work.
   • B.Feed rate; it dominates tool life because a heavier feed thickens the chip and drives cutting forces higher than speed ever can.
   • C.Cutting speed; raising it shortens tool life fastest, because speed drives cutting-interface temperature and the wear that ends tool life is temperature-driven.✓ Answer
   • D.All three change tool life by the same amount, so any one of them may be increased with equal consequences.

   The three cutting variables affect tool life in the order speed > feed > depth of cut, because speed drives cutting-interface temperature, and the wear mechanisms that end tool life are temperature-driven. That is why the standard response to premature tool failure is to reduce RPM first, and why more metal per hour is usually bought with feed and depth of cut rather than speed.

   Source: NIMS Machining Level I Standards, KSAO 7.1 Cutting Theory — speeds, feeds, depth of cut and tool lifeReport a problem with this question

8. 8. Why is negative rake geometry commonly chosen for carbide tooling on hard material and interrupted cuts?

   • A.It lowers cutting force and power consumption, which lets a light, low-powered machine take much heavier cuts than positive rake ever could.
   • B.It increases the effective relief angle at the flank, so the tool clears the work and no longer rubs the finished surface.
   • C.It forces the chip to curl tightly against the workpiece, which is how a negative-rake tool breaks chips without a chipbreaker.
   • D.It puts more tool material behind the edge and loads it in compression, strengthening brittle carbide against the shock of hard material and interrupted cuts.✓ Answer

   Positive rake cuts more freely and lowers cutting force, but it leaves a thin, weakly supported wedge at the edge. Negative rake trades higher cutting force and more power draw for a much stronger, compressively loaded edge, which is what brittle carbide needs for hard material, scale and interrupted cuts — and it is also why negative rake demands a rigid machine and setup.

   Source: NIMS Machining Level I Standards, KSAO 7.1/7.2 — cutter geometry (rake angle) and cutting tool materialsReport a problem with this question

9. 9. What is the consequence of grinding too little relief (clearance) angle on a single-point lathe tool?

   • A.The flank rubs the work behind the edge, generating friction heat, a poor finish and rapid flank wear.✓ Answer
   • B.The cutting edge becomes so thin and unsupported that it breaks down almost immediately under a normal cutting load.
   • C.The chip curls too tightly and packs into the tool, so the operator must stop and clear it after every pass.
   • D.The tool cuts freely but leaves an oversize part, because the workpiece deflects away from the unsupported edge.

   Relief angle exists only to keep the tool's flank from touching the work behind the cutting edge. Too little relief makes the heel rub, which produces friction heat, a poor finish and rapid flank wear; too much relief removes support and lets the edge break down — which is why the two errors have opposite symptoms and opposite fixes.

   Source: NIMS Machining Level I Standards, KSAO 7.1/7.2 — cutter geometry (relief and clearance angles)Report a problem with this question

10. 10. A long, slender shaft is being finish turned and the surface shows chatter marks with obvious tool pressure. Which tool-geometry change most directly reduces the radial pressure of the cut?

    • A.Increase the nose radius substantially, since a larger radius always improves surface finish no matter how rigid or flexible the setup is.
    • B.Use a smaller nose radius on the finishing tool, since a large radius lengthens tool-work contact and raises the radial force that deflects the part.✓ Answer
    • C.Increase the depth of cut so the tool stays fully engaged and cannot be deflected by the springing workpiece.
    • D.Grind a much larger side relief angle so the tool rides over the vibration instead of digging into the surface.

    A larger nose radius smooths the finish by overlapping the feed marks, but it also lengthens the contact between tool and work and raises radial (pushing-off) force. On a flexible part that extra force deflects the work and starts chatter, so the finishing answer is a smaller radius with a light depth of cut — and added support such as a follower rest.

    Source: NIMS Machining Level I Standards, KSAO 7.1 — cutter geometry (nose radius), tool pressure and surface finishReport a problem with this question

11. 11. Which statement comparing cemented carbide cutting tools with high-speed steel is FALSE?

    • A.Carbide keeps its hardness at higher cutting temperatures than high-speed steel does.
    • B.Carbide is more brittle than high-speed steel, so it needs a rigid setup and good support behind the cutting edge.
    • C.Carbide must be run at lower cutting speeds than high-speed steel in the same material.✓ Answer
    • D.Carbide tooling normally costs more per cutting edge than an equivalent high-speed steel tool.

    Hot hardness is the whole point of carbide: because it holds its hardness at temperatures that soften HSS, it is run at substantially HIGHER surface speeds, which is its main productivity advantage along with longer tool life. Its real limitations are brittleness and cost, not a speed penalty.

    Source: NIMS Machining Level I Standards, KSAO 7.2 Tooling — cutting tool materials (carbide vs high-speed steel)Report a problem with this question

12. 12. Why are diamond cutting tools not used to machine steel and other ferrous metals?

    • A.Diamond is not hard enough to cut hardened ferrous alloys, so its edge dulls before it can finish even a single pass.
    • B.Diamond tools cannot be manufactured with a cutting edge sharp or accurate enough for ferrous work.
    • C.Ferrous metals are magnetic, and the magnetic pull tears the diamond grit out of its bonding matrix.
    • D.Carbon from the diamond diffuses into the iron at cutting temperature, so the edge wears away rapidly.✓ Answer

    Diamond is the hardest tool material, but it is pure carbon and iron has a strong chemical affinity for carbon at cutting temperatures, so the tool literally dissolves into the chip. Diamond is therefore reserved for non-ferrous and non-metallic work (aluminum, brass, plastics, composites), while CBN/Borazon is the superabrasive used on hardened ferrous material.

    Source: NIMS Machining Level I Standards, KSAO 7.2 Tooling — cutting tool materials (diamond and CBN applications)Report a problem with this question

13. 13. A 2.500 in diameter steel bar is being turned. The cutting speed selected for the tool and material is 90 SFM. Using RPM = (3.82 x CS) / D, what spindle speed should be set?

    • A.138 RPM✓ Answer
    • B.344 RPM
    • C.55 RPM
    • D.275 RPM

    (3.82 x 90) / 2.500 = 343.8 / 2.500 = 137.5, rounded to 138 RPM. On a lathe the D in the formula is the diameter of the WORKPIECE being cut, not the tool, because it is the work surface that passes the cutting edge; 344 RPM is the classic error of never dividing by the diameter.

    Source: NIMS Machining Level I Standards, KSAO 7.1 — speed selection; RPM = (3.82 x CS) / D (equivalently (CS x 4) / D)Report a problem with this question

14. 14. A four-flute end mill is running at 900 RPM with a chip load of .003 in per tooth. What table feed should be set?

    • A.2.7 IPM
    • B.10.8 IPM✓ Answer
    • C.43.2 IPM
    • D.3.6 IPM

    Milling feed is IPM = feed per tooth x number of teeth x RPM = .003 x 4 x 900 = 10.8 IPM. The tooth count belongs in the calculation because every flute takes its own bite per revolution; leaving it out gives the 2.7 IPM trap, and applying it twice gives 43.2 IPM.

    Source: NIMS Machining Level I Standards, KSAO 7.1 — feed selection; IPM = feed per tooth x number of teeth x RPMReport a problem with this question

15. 15. A lathe is making one 9.0 in long pass at 300 RPM with a feed of .010 IPR. Using T = L / (f x N), how long does the pass take?

    • A.0.33 minutes
    • B.30 minutes
    • C.3.0 minutes✓ Answer
    • D.1.5 minutes

    f x N = .010 IPR x 300 RPM = 3.0 in per minute of tool travel, so T = 9.0 / 3.0 = 3.0 minutes. The formula works because multiplying inches per revolution by revolutions per minute converts the lathe's IPR feed into the inches-per-minute travel rate that the length of cut is divided by.

    Source: NIMS Machining Level I Standards, KSAO 7.1 — cutting time T = L / (f x N)Report a problem with this question

16. 16. In which units is feed normally designated on an engine lathe and a drill press, and in which units on a milling machine?

    • A.Lathe and drill press in inches per minute, while the milling machine is the one machine whose feed is stated in inches per revolution.
    • B.All three machines state feed in inches per minute, because feed is always a rate of table or spindle travel over time.
    • C.All three machines state feed in inches per revolution, and the control converts that value to a travel rate internally.
    • D.Lathe and drill press in inches per revolution; milling machine in inches per minute, since a milling cutter has several teeth.✓ Answer

    On the lathe and drill press a single tool or workpiece revolution produces one advance, so feed is naturally stated per revolution (IPR). A milling cutter has several teeth, each taking its own chip, so feed is stated as table travel per minute (IPM) and is built up from feed per tooth x teeth x RPM.

    Source: NIMS Machining Level I Standards, KSAO 7.1 — feed designation (IPR on lathe/drill press, IPM on milling machine)Report a problem with this question

17. 17. What is the major disadvantage of climb (down) milling on a manual milling machine with a conventional leadscrew?

    • A.The cutter pulls the work into itself, and leadscrew backlash lets the table lurch forward.✓ Answer
    • B.It gives a poorer surface finish and shorter cutter life, because each tooth enters the cut at maximum chip thickness and leaves it at zero.
    • C.It requires the table to be fed against the direction of cutter rotation, which nearly doubles the horsepower the machine must supply.
    • D.It generates far more heat at the cutting edge, so a flood of coolant is mandatory on every climb-milling cut.

    In climb milling the cutter rotation and the feed act in the same direction, so the cutter tends to drag the table along. Any backlash in a manual leadscrew lets the table jump into the cutter, which can break the tool or the part; that is the safety reason climb milling is reserved for machines with backlash eliminators or ball screws, even though it otherwise gives a better finish and longer tool life.

    Source: NIMS Machining Level I Standards, KSAO 7.1/7.2 — cutter presentation, climb (down) vs conventional (up) millingReport a problem with this question

18. 18. Why must cutting fluid applied to a carbide tool be delivered as a copious, uninterrupted flood?

    • A.Carbide cannot cut at all without lubrication, so if the flow ever stops the insert will immediately weld itself to the workpiece surface.
    • B.Intermittent coolant thermally shocks the hot carbide and can crack the cutting edge.✓ Answer
    • C.The only purpose of the fluid is to wash chips out of the cut, and a weak stream simply lets chips pile up around the tool.
    • D.Carbide rusts very rapidly at cutting temperature, and an unbroken film of fluid is what keeps oxygen away from the edge.

    Carbide is hard and heat resistant but brittle and a poor conductor, so a splash of coolant hitting a red-hot edge and then stopping sets up steep temperature cycling that opens thermal (comb) cracks across the edge. Either flood it continuously or run it dry — the failure mode comes from the temperature swing, not from the heat itself.

    Source: NIMS Machining Level I Standards, KSAO 7.1/7.5 — cutting fluid application to carbide tooling (thermal shock and thermal cracking)Report a problem with this question

Practice questions based on NIMS/ANSI 101-2001, Duties and Standards for Machining Skills Level I, and the published content of the NIMS Machining Level I theory exams, together with standard precision-machining practice. NIMS is a mark of the National Institute for Metalworking Skills; this site is not affiliated with or endorsed by NIMS. Machining Level I is a set of separate credentials, and most of them also require a hands-on performance test that this bank does not cover. The NIMS theory exams are open-reference, but questions here never depend on recalling a handbook table value, a citation number or a machine rating — always work from the print in front of you, your employer's written procedures, and the machine's own documentation, and confirm current requirements before testing. About the NIMS machining credentials →