Blueprint Reading, Symbols, and Layout
Core Concepts
Candidates must read welding symbols per AWS A2.4: the reference line, arrow, tail, groove and fillet symbols, size and length placement, the distinction between arrow side and other side, all-around and field-weld flags, and supplementary contour and finish symbols. You should interpret orthographic and isometric views, first-angle vs. third-angle projection, dimensioning and tolerances, and basic geometric dimensioning and tolerancing. Layout skills include datum selection, baseline layout, and allowance for shrinkage and distortion. Also know how to read a bill of materials, weld maps, and structural drawings.
Traps
Symbol placement is the classic trap: a fillet symbol below the reference line means the weld goes on the arrow side; above means the other side. A circle at the symbol junction means weld all around; a flag means field weld. Size is always shown to the left of the symbol, length to the right. Confusing first-angle and third-angle projection is another common distractor.
Worked Example / Rule of Thumb
Read a symbol left to right: size, then symbol, then length and pitch. Example: a triangle below the line with "1/4" on the left and "6" on the right means a 1/4-in. fillet on the arrow side, 6 in. long. Rule: "below the line = arrow side; above the line = other side."