ITI/NCVT Tool & Die Maker (AITT Theory) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Class D fire

Fire involving combustible metals such as magnesium, sodium or aluminium swarf; extinguish with dry powder or dry sand, never with water or CO2, because water reacts and can explode.

Grinding wheel ring test

Before mounting, suspend a clean wheel on a finger and tap it lightly 45 degrees from the vertical axis; a clear ring means sound, a dead thud means cracked and reject.

Lockout tagout

Isolate all energy sources with a personal lock and tag before repairing or clearing a machine; only the person who applied the lock removes it, preventing accidental start-up.

5S housekeeping

Sort, set in order, shine, standardize and sustain: a workplace discipline that removes unneeded items, marks locations, cleans equipment and audits results to reduce accidents and lost time.

Eutectoid carbon percentage

Plain carbon steel with 0.8% carbon is eutectoid; on slow cooling it transforms to 100% pearlite, giving maximum hardness and strength among slowly cooled plain carbon steels.

Case carburizing

Packing or gas carburizing heats low-carbon steel to about 900-950 °C in a carbon-rich atmosphere, diffusing carbon to 0.5-1.5 mm depth; quenching then hardens only the case.

Tempering purpose

Reheating a hardened steel below the lower critical temperature and cooling reduces internal stress and brittleness, trades some hardness for toughness, and is done immediately after quenching.

HSS 18-4-1 composition

High-speed steel containing about 18% tungsten, 4% chromium and 1% vanadium; it retains hardness up to roughly 600 °C, allowing cutting speeds several times those of carbon steel.

Vernier least count

Least count = 1 main scale division minus 1 vernier scale division; for a 49 mm vernier divided into 50 parts it equals 0.02 mm, the smallest reading the caliper can show.

Micrometer least count

Least count = screw pitch divided by number of thimble divisions; a 0.5 mm pitch screw with a 50-division thimble reads to 0.01 mm, with a vernier sleeve giving 0.001 mm.

Sine bar angle formula

The angle is found from sin θ = h/L, where h is the height of the slip gauge stack and L is the centre distance between the sine bar rollers, usually 100 or 200 mm.

Taylor principle gauges

The GO gauge is made to the maximum material limit and checks the full feature; the NO-GO gauge is made to the least material limit and should not enter, so both limits are controlled.

Cutting speed formula

Cutting speed V = πDN/1000 m/min, where D is the workpiece or cutter diameter in mm and N is spindle speed in rev/min; rearrange to N = 1000V/(πD).

Climb milling

In climb (down) milling the cutter rotates in the same direction as the feed, so teeth start at full depth; it gives a better finish but needs a backlash eliminator to avoid breakage.

Simple indexing formula

Simple indexing on a dividing head uses 40/N turns of the crank, where N is the number of divisions required; 40 is the worm-to-table ratio of a standard Brown and Sharpe head.

Grinding wheel marking

A marking such as A 46 K 5 V means aluminium oxide abrasive, 46 grit, K medium grade, 5 fairly dense structure and V vitrified bond; letters progress soft to hard from A to Z.

3-2-1 locating principle

Three locating points on the base plane, two on the side plane and one on the end plane remove all six degrees of freedom, fully locating a rectangular workpiece without over-constraint.

Jig versus fixture

A jig locates and holds the workpiece and also guides the cutting tool through bushes; a fixture locates and holds but relies on a preset tool or machine axis for position.

Blanking versus piercing

In blanking the punched-out piece is the product and the surrounding sheet is scrap; in piercing the hole is the product and the piece removed is scrap, though both use the same die action.

Blanking force formula

Cutting force F = L × t × τ, where L is the cut perimeter in mm, t the sheet thickness in mm and τ the shear strength in N/mm²; punch force must exceed this for clean shearing.

Die clearance rule

Clearance per side is typically 3-8% of sheet thickness for blanking and piercing of mild steel, balanced so the punch clears the die without excessive burr or force.

Compound die

A compound die performs blanking and piercing in one press stroke at a single station, producing a part with accurate hole-to-outline relationship and high output per stroke.

G02 and G03 codes

G02 moves the tool clockwise and G03 counter-clockwise along a circular arc; the arc is defined by end point plus radius R, or by arc centre offsets I and J.

Cutter radius compensation

G41 compensates to the left of the programmed path and G42 to the right, allowing the part program to use the part outline while the control offsets by tool radius; G40 cancels.

Absolute and incremental modes

G90 interprets coordinates as absolute positions from a fixed origin, while G91 interprets them as incremental distances from the current point; mixing modes without care causes positioning errors.

CAM post-processor role

A post-processor converts neutral CAM toolpath data into machine-specific G-code, applying the particular machine kinematics, control dialect, feed and tool-change formats.

First angle projection

In first-angle projection the object sits between the observer and the plane, so the top view is placed below the front view and the left view appears on the right.

Geometric tolerance MMC

Maximum material condition is the limit at which the feature has the most material, for example the smallest hole or largest shaft; applying it allows bonus tolerance as the feature departs.

Surface roughness Ra

Ra is the arithmetical mean deviation of the roughness profile from its mean line over the sampling length, expressed in micrometres; lower Ra means a smoother surface.

Machining time turning

For a single longitudinal cut, machining time T = L/(f × N), where L is the tool travel in mm including approach, f is feed in mm/rev and N is spindle speed in rev/min.

Gear module formula

Module m = pitch circle diameter divided by number of teeth in mm; addendum equals m and dedendum equals 1.25m, so standard metric gears mesh with equal modules.

Torque and power

Torque T = F × r in N·m; rotational power P = 2πNT/60 in watts; for the lathe the cutting power equals cutting force times cutting speed divided by efficiency.