ITI/NCVT Tool & Die Maker (AITT Theory) cheat sheet

Fire classes: A = solid combustibles (water), B = flammable liquids (foam, CO2, dry powder), C = flammable gases, D = combustible metals (dry sand or dry powder only; never water); electrical fires need CO2 or dry powder.

Fire triangle = fuel + oxygen + heat; removing any one leg stops combustion. Foam blankets to exclude oxygen; water cools to remove heat.

Guarding rules: chucks, spindles, belts and gears need fixed or interlocked guards; press brakes use light curtains or two-hand control; interlock switches must never be bypassed.

Grinding wheel checks before mounting: ring test, wheel speed rating above machine speed, no cracks, guard covering at least half the wheel, tool rest gap within 3 mm.

Electrical safety: 30 mA RCD/ELCB for portable tools; earth continuity test; lockout/tagout with a personal lock before maintenance or jam clearing.

Waste segregation: metal swarf, oil-soaked rags, used coolant and batteries are separate hazardous streams; oil and coolant must never be poured into drains.

PPE: safety glasses for grinding, chipping and drilling; no gloves, ties or rings near rotating shafts; hearing protection in high-noise zones; leather apron for hot work.

First aid: eye splash - flush at an eyewash for at least 15 minutes and never rub; burns - cool with running water 10-20 minutes; report every injury and near miss.

5S housekeeping: sort, set in order, shine, standardize, sustain; keep aisles and exits clear, tools on shadow boards, spill absorbent near machines.

Fe-Fe3C diagram: eutectoid at 0.8% carbon and 723 °C (pearlite); hypoeutectoid steels below 0.8% C contain proeutectoid ferrite, hypereutectoid steels above 0.8% C contain cementite.

Carbon steel groups: low carbon 0.05-0.25% (mild steel, tough, formable), medium carbon 0.30-0.60% (hardenable by quenching), high carbon 0.60-1.50% (tools, wear resistant).

Annealing: heat 20-50 °C above the upper critical temperature, soak, then cool slowly in the furnace - removes stress, softens, refines grain and improves machinability.

Normalizing: heat 30-50 °C above the critical temperature and cool in still air - finer pearlite than annealing, higher strength, used to refine overheated or distorted structures.

Hardening: austenitize (727 °C + 30-50 °C), then quench in water for carbon steel or oil for alloy steel; martensite forms, hard and brittle, so tempering must follow.

Tempering: reheat below the lower critical temperature (150-650 °C), hold and cool; 150-250 °C favours wear resistance for tools, higher temperatures favour toughness.

Carburizing: low-carbon steel heated to 900-950 °C in a carbon-rich medium for a 0.5-1.5 mm case, then quenched and tempered; the core stays tough.

Nitriding: 500-550 °C in ammonia gives a very hard 0.1-0.5 mm case without quenching; requires alloy steel with Al, Cr or Mo and gives low distortion.

Identification tests: spark test for carbon content, file test for hardness, magnetic test for ferritic steels, Brinell HB for castings, Rockwell HRC for hard tools, Vickers HV for thin cases.

Vernier least count = 1 MSD − 1 VSD, usually 0.02 mm. Reading = main scale + (coinciding vernier division × LC) − zero error.

Micrometer least count = pitch / thimble divisions = 0.5 / 50 = 0.01 mm. Reading = sleeve reading + (thimble division × 0.01); always check zero error on the anvil.

Dial indicator least count is typically 0.01 mm (0.001 mm for precision models); used with a magnetic base for runout, flatness and alignment checks.

Fits: clearance (hole larger than shaft), transition (hole and shaft limits overlap), interference (shaft larger than hole). Tolerance = upper limit − lower limit; allowance = minimum clearance.

Hole basis system: the H hole is standard and the shaft letter fixes the fit - H7/g6 sliding, H7/h6 locational clearance, H7/p6 light press.

Metric tap drill size = nominal diameter − pitch; M10 × 1.5 uses an 8.5 mm drill. This gives roughly 75% thread engagement.

GO/NO-GO gauges follow Taylor's principle: the GO gauge is made to the maximum material limit and must enter; the NO-GO gauge is made to the least material limit and must not enter.

Files: double cut for rapid stock removal, single cut for finishing and sharpening, draw filing for flat surfaces and burr removal; clean with a file card.

Surface roughness Ra is the arithmetic mean deviation of the profile in micrometres: N5 ≈ 0.4 µm, N7 ≈ 1.6 µm; lower Ra means a finer finish.

Cutting speed V = πDN/1000 m/min, so N = 1000V/(πD) rpm with D in mm. Typical HSS in mild steel ≈ 25-35 m/min; carbide 100-300 m/min.

Lathe taper turning by tailstock set-over: S = L × (D − d) / (2 × l), where L = full workpiece length and l = taper length; use the compound rest for steep tapers.

Lathe thread cutting: gear ratio = workpiece pitch / leadscrew pitch; engage the half-nut at the same chasing-dial mark on every pass to keep the tool in the helix.

Up (conventional) milling: cutter rotates against the feed, chips start thin, safer where backlash exists. Down (climb) milling gives a better finish but needs a backlash eliminator.

Simple indexing = 40/N turns of the index crank; for N = 30 use 1 full turn plus 10 holes on a 30-hole circle. Use compound or differential indexing for primes outside the plate range.

Drilling: standard point angle 118° for general steel, 135° split point for hard materials, lip clearance 8-12°; drill speed ≈ 25-30 m/min in mild steel with HSS.

Reaming allowance is 0.1-0.2 mm on diameter; use about half the drilling speed and twice the feed, with cutting fluid, and never rotate a reamer in reverse.

Grinding wheel marking A 46 K 5 V: abrasive (A = Al2O3, C = SiC), grit number, grade (A soft to Z hard), structure (1 dense to 15 open), bond (V vitrified, B resinoid, R rubber).

Surface grinding: wheel speed 30-35 m/s and work speed 10-20 m/min; dress with a diamond dresser and balance the wheel before mounting to avoid vibration.

3-2-1 principle: three points on the primary base plane, two on the secondary side plane and one on the tertiary end plane remove all six degrees of freedom; avoid redundant fixed locators.

A jig locates, holds and guides the tool through hardened bushes; a fixture locates and holds only, with tool position set by the machine or a preset tool. Jigs suit drilling, fixtures suit milling and turning.

Locators: flat pads and buttons, cylindrical pins, V-blocks for round parts, diamond pins for two-hole location; make wear surfaces relieved and renewable.

Clamping rules: clamp opposite the main cutting force and directly over a support point, not across an unsupported span; use toggle, cam, strap, screw or hydraulic clamps.

Drill bushings: press-fit (fixed), renewable slip and liner types; the bushing bore equals the drill diameter, and head clearance plus chip clearance must be provided.

Blanking and piercing clearance per side is about 3-8% of sheet thickness for mild steel; too little causes burr and pick-up, too much causes roll-over and a poor edge.

Blanking: punch size = blank size, die opening = punch + 2 × clearance. Piercing: punch size = hole size, die opening = punch + 2 × clearance.

Bending: bend allowance BA = (π/180) × bend angle × (R + K·T), with K ≈ 0.33-0.5; compensate springback by over-bending or bottoming.

Injection mould path: sprue → runner → gate → cavity; provide 1-3° draft, cooling channels, ejector pins and shrinkage allowance (about 2% for PP, 0.5% for PS).

Blanking force F = L × t × τ (N), where L = sheared perimeter in mm, t = sheet thickness in mm and τ = shear strength in N/mm²; press tonnage must exceed F with a 20-30% margin.

A shear angle ground on the punch spreads the cut and lowers peak force; stepped or staggered punches give the same effect and reduce shock on the press.

Die set components: die shoe, punch holder, guide pillars and bushes, bolster plate, stripper, punch plate and back-up plate; guide pillars maintain punch-to-die alignment.

Die clearance per side ≈ 3-8% of thickness for mild steel, increasing with shear strength; verify by blue matching or feeler gauge during tryout.

Progressive die: the strip advances one station per stroke with separate operations at each station. Compound die: blanking and piercing in one station in a single stroke.

Strippers remove the strip from the punch: fixed stripper for thick sheet, spring stripper, urethane stripper; pilots locate the strip before piercing starts.

Die materials: OHNS for small dies, HCHCr (D2/D3 type) for high wear, carbide inserts for long runs; harden to 58-62 HRC and temper to relieve stress.

Press safety: two-hand control, light curtains, fixed guards and no hand feeding into the die; set shut height and check bottom dead centre before running.

Die maintenance: sharpen punches and dies by surface grinding, maintain clearance, polish draw radii, clear slug build-up and record strokes between sharpenings.

Common G-codes: G00 rapid, G01 linear feed, G02/G03 circular CW/CCW, G04 dwell, G17/G18/G19 plane selection, G20/G21 inch/mm, G28 home, G90/G91 absolute/incremental.

Feed and speed codes: G94 feed per minute (mm/min), G95 feed per revolution (mm/rev), G96 constant surface speed (m/min), G97 constant rpm, G50 maximum spindle clamp.

Compensation: G41 cutter radius left, G42 right, G40 cancel; G43 tool length positive, G44 negative, G49 cancel; D and H registers hold the offset values.

Canned cycles: G81 drilling, G82 spot drilling with dwell, G83 peck drilling, G84 tapping, G76 fine boring; G80 cancels the cycle.

Coordinates: machine zero (reference point), work zero (G54-G59) and G92 setting; Z is always along the spindle and the right-hand rule fixes X and Y.

Program structure: program number, safe start block, tool call (T/M06), spindle (M03/M04), coolant (M08), machining blocks, M05/M09, then M30 to end and rewind.

CAM workflow: CAD model → stock definition → toolpath strategy → simulation and gouge check → post-processor → G-code → DNC transfer to the machine.

CAD exchange formats: DXF/DWG for 2D drawings, IGES and STEP for 3D neutral models, STL for mesh and 3D printing; parametric models retain feature history and dimensions.

Circular interpolation needs I and J (arc centre offsets from the start point) or the radius R; helical interpolation combines circular motion with a Z-axis feed.

First-angle projection places the object between observer and plane, so the top view goes below the front view and the left side view appears on the right. Third angle puts the top view above the front view.

Line types: continuous thick = visible outline, dashed = hidden edges, chain thin = centre lines and pitch circles, chain thick = cutting plane, wavy = break line.

Scale: representative fraction RF = drawing length / actual length; 1:2 is reducing, 2:1 enlarging; state the scale and units in the title block.

Section views: full, half, offset, revolved and removed; hatch at 45° with even spacing, hatch adjacent parts in opposite directions, and omit hidden lines unless needed.

Dimensioning: extension lines from the feature, dimension line with arrowheads, leader for notes; datum dimensioning suits production, and fits appear as H7/g6.

Geometric tolerances: form (straightness, flatness, circularity, cylindricity), orientation (parallelism, perpendicularity, angularity), location (position, concentricity, symmetry) and runout.

Surface texture symbol: Ra value in µm with the machining process and lay symbol; a general note covers surfaces not individually marked.

Thread callout: M20 × 2.5 LH means metric thread, 20 mm major diameter, 2.5 mm pitch, left hand; minor diameter ≈ nominal − 1.0825 × pitch.

Title block and BOM: part name, drawing number, material, scale, revision, general tolerances and author; the BOM lists item, description, quantity and material.

Cutting speed V = πDN/1000 m/min; spindle speed N = 1000V/(πD) rpm; feed f in mm/rev; depth of cut for turning = (D − d)/2.

Turning time T = L/(f × N) minutes, where L = approach + job length + overtravel; milling time T = L/(f × z × N) with feed per tooth f and z teeth.

Taper: tan(α/2) = (D − d)/(2 × L); sine bar sin θ = h/L; a 100 mm sine bar is normally used for angles up to 45°.

Gear: module m = PCD / T; addendum = m, dedendum = 1.25m, whole depth = 2.25m; centre distance = m(T1 + T2)/2.

Indexing: crank turns = 40/N; angular indexing gives 360/40 = 9° per crank turn; differential indexing uses change gears for divisions outside the plate range.

Stress σ = F/A (N/mm²), strain ε = ΔL/L, Young's modulus E = σ/ε; torque T = F × r; rotational power P = 2πNT/60.

Work, power and efficiency: W = F × s (J), P = W/t (W), η = output/input × 100%; cutting power ≈ cutting force × cutting speed.

Mensuration: circle area = πd²/4, circumference = πd, cylinder volume = πr²h; Pythagoras c² = a² + b²; density = mass/volume.

Temperature and expansion: °F = (9/5)°C + 32; K = °C + 273.15; ΔL = α·L·ΔT.