RRB ALP Fitter Trade — Complete CBT-2 Study Guide

• Fitting is the process of assembling machine parts through hand/machine operations (filing, chipping, scraping, grinding) to achieve precise fits between mating components — types of fit include Clearance fit (loosest, easy assembly/disassembly), Transition fit (may be slightly loose or tight), and Interference fit (tightest, requires force/press-fitting, used for permanent assemblies). • Filing operations remove small amounts of material to achieve a required size/finish; files are classified by cut (single-cut for finishing, double-cut for faster stock removal) and grade (rough, bastard, second-cut, smooth — increasing fineness). • Marking-out tools establish reference lines/points before machining: scriber (draws fine lines), surface plate + surface gauge (establishes height reference), punch (marks center points for drilling) — accurate marking-out prevents costly machining errors downstream. • Chipping uses a hand hammer and chisel to remove excess/unwanted material, typically where machine tools cannot reach — flat chisel for general flat-surface work, cross-cut chisel for cutting grooves/keyways.

• Drilling produces round holes using a rotating cutting tool (twist drill); drill point angle is typically 118° for general-purpose work in mild steel, with a smaller angle (~90°) for softer materials and larger angle for harder materials. • Cutting speed for drilling depends on material and drill diameter — too high a speed overheats/dulls the drill bit prematurely, too low reduces productivity; proper cutting fluid/coolant is essential for extended tool life and finish quality, especially in steel. • Tapping cuts internal threads into a pre-drilled hole using a tap tool; the tap drill size must be smaller than the finished thread's major diameter by an amount equal to the thread pitch (approximately), leaving correct material for the thread crest to form. • Taper tap, second (plug) tap, and bottoming (plug) tap are the three-tap set used in sequence for blind holes — taper tap starts the thread gradually, bottoming tap completes threading closer to the hole's bottom.

• Arc welding uses an electric arc between an electrode and the workpiece to generate intense heat, melting both the base metal and filler (electrode) material to form a fused joint upon cooling. • Gas welding (oxy-acetylene) uses a controlled flame from burning acetylene with oxygen — offers good control for thin sheet metal and pipe work, though generally slower than arc welding for thicker sections. • Common welded joint types: Butt joint (edges meet end-to-end, in the same plane), Lap joint (one piece overlaps another), Tee joint (perpendicular pieces forming a "T" shape), Corner joint (pieces meet at an angle, forming a corner). • Weld defects to identify: Porosity (trapped gas bubbles in the weld, weakens it), Undercut (a groove melted into the base metal at the weld toe, reducing joint strength), Incomplete fusion/penetration (weld metal fails to fully bond/penetrate the base metal).

• Vernier caliper measures internal, external, and depth dimensions; Least Count = value of 1 Main Scale Division ÷ total number of Vernier Scale divisions — standard vernier caliper LC = 0.02mm or 0.05mm depending on the instrument. • Micrometer (screw gauge) measures with higher precision than a vernier caliper; Least Count = Pitch of the screw ÷ number of divisions on the thimble (circular scale) — standard LC = 0.01mm. • Zero error correction: Positive zero error (scale reads above true zero when jaws/anvils are closed) is SUBTRACTED from the observed reading; Negative zero error is ADDED to the observed reading — always check and correct zero error before taking measurements. • Surface plate provides a precise, flat reference surface for inspection/marking-out work — typically made of cast iron or granite, checked periodically for flatness using a precision spirit level or optical flat. • Angle plates, V-blocks, and clamps are precision workholding fixtures used to hold a workpiece securely and accurately during marking-out, inspection, or machining operations.