This cheat sheet covers the basic welding symbols and joint types used on engineering and fabrication drawings. Students need it because welding instructions are often shown with compact symbols instead of long written notes. Reading these symbols correctly helps a builder know what type of weld to make, where to place it, and how large it should be.
It is especially useful for design, manufacturing, robotics, and shop projects.
Key Facts
- The reference line is the main horizontal line of a welding symbol, and weld information is placed above or below it.
- A weld symbol below the reference line means the weld is made on the arrow side of the joint.
- A weld symbol above the reference line means the weld is made on the other side of the joint.
- A fillet weld symbol is a right triangle, and its size is usually written to the left of the symbol, such as 1/4 fillet weld.
- A groove weld symbol shows the prepared edge shape, such as square, V, bevel, U, or J groove.
- The length of a weld is written to the right of the weld symbol, such as 3 meaning a 3 inch weld.
- Intermittent welds use length and pitch notation, such as 2-6 meaning 2 inch weld segments spaced 6 inches center to center.
- A circle at the junction of the arrow and reference line means weld all around the joint.
Vocabulary
- Welding symbol
- A complete drawing notation that shows the weld type, location, size, length, and other instructions.
- Weld symbol
- The small shape inside a welding symbol that identifies the type of weld, such as fillet, groove, plug, or spot.
- Reference line
- The horizontal line that carries weld symbols and separates arrow-side information from other-side information.
- Arrow side
- The side of the joint that the arrow points to on the drawing.
- Fillet weld
- A triangular weld used to join two surfaces that meet at about a right angle, such as a T joint or lap joint.
- Groove weld
- A weld made in a prepared opening or groove between two parts to join them along an edge.
Common Mistakes to Avoid
- Confusing weld symbol with welding symbol is wrong because the weld symbol is only the small shape, while the welding symbol includes the reference line, arrow, tail, and dimensions.
- Putting an arrow-side weld above the reference line is wrong because AWS notation places arrow-side weld information below the reference line.
- Reading pitch as weld length is wrong because in notation like 2-6, the first number is segment length and the second number is spacing center to center.
- Ignoring the tail is wrong because the tail may include important process or specification notes such as SMAW, GMAW, or a welding procedure reference.
- Assuming every joint uses the same weld type is wrong because butt, lap, T, corner, and edge joints can require different weld symbols and preparation.
Practice Questions
- 1 A fillet weld symbol is below the reference line with 1/4 written to the left and 3 written to the right. What size and length of weld is required, and on which side is it placed?
- 2 An intermittent fillet weld is labeled 2-6 to the right of the weld symbol. What is the weld segment length and what is the pitch?
- 3 A weld symbol appears above the reference line, and a circle appears where the arrow meets the reference line. What do these two symbol features mean?
- 4 A designer chooses a lap joint for two overlapping plates instead of a butt joint. Explain why the weld symbol and side placement must still be read carefully before fabrication.
Understanding Welding Symbols & Joint Types Reference
A welding symbol is only one part of the manufacturing instruction. The drawing may include dimensions, material names, general notes, and a welding procedure specification. The procedure tells the welder which process, filler metal, shielding gas, current range, and position are allowed.
A tail on a welding symbol can point to one of these instructions or name a process. This matters because the same joint shape can need different settings when it is made from thin sheet steel, thick structural steel, stainless steel, or aluminum.
The arrow should clearly point to the actual joint. If it points at the wrong plate or edge, a correct looking weld can be placed in the wrong location.
Joint type affects strength, access, cost, and the amount of heat put into the parts. A butt joint joins pieces in the same plane. It is common in plates, pipes, and sheet metal panels.
A lap joint overlaps two pieces and is often easier to fit, though moisture can collect in the overlap if the product is used outdoors. A tee joint connects one part near perpendicular to another. It appears in frames, brackets, shelves, and robot structures.
Corner joints form boxes and cabinets. Edge joints join nearby edges of thin material.
Engineers choose a joint by considering the direction of the load. A weld that is strong under a pulling force may behave differently when a part is bent, twisted, or repeatedly vibrated.
Groove preparation controls how deeply the molten metal can reach into a joint. Thick parts often need bevels because a simple square gap may not allow enough penetration. The narrow space at the bottom is called the root opening.
It must be controlled carefully. If it is too small, the weld may not fuse through the joint. If it is too large, molten metal can fall through or require extra filler.
A backing strip may support the root during welding. These details are important on bridges, pressure vessels, vehicle frames, and any part where a hidden lack of fusion could cause failure. A drawing symbol may show the edge shape, but fit up and cleanliness still decide whether the real weld is sound.
Weld size is not just a number written on paper. For a fillet weld, the leg size affects the area of metal that resists force. Larger welds can carry more load, but they use more time and filler metal.
They also add heat, which can warp thin parts. Intermittent welds are useful when a full continuous weld is unnecessary. They can reduce distortion and weight, but the spacing must be followed exactly so the load is shared as intended.
Students should practice reading a symbol in a fixed order. First identify the joint and the arrow location. Next identify the weld form, size, length, spacing, contour, and any finishing requirement.
Finally check nearby notes for units, process rules, and inspection requirements. In shop work, inspect for cracks, holes, undercut, poor fusion, and excessive spatter before assuming a weld is acceptable.