How to Read and Write the Weld Symbols on Your Own Drawing
A weldment drawing without weld symbols is a suggestion. The shop still has to decide what weld goes where, and since it carries the risk if the joint fails, it will decide generously. You pay for the generosity in weld metal, distortion and hours.
Ten minutes of symbols on the drawing is the highest return per minute available to a weldment buyer.
The parts of the symbol
Arrow. Points at the joint. Where the arrowhead lands is where the weld goes, and on a joint with a prepared side the arrow breaks towards the member to be prepared.
Reference line. The horizontal line the symbol is built on. Always horizontal, regardless of how the arrow runs.
Weld symbol. The small shape on the reference line that says what kind of weld. A triangle for a fillet, a square for a square groove, a V for a V groove, a half V for a bevel, and so on.
Position relative to the line. In the AWS convention the symbol below the reference line applies to the arrow side. The symbol above the line applies to the other side. A symbol on both sides means weld both sides. ISO uses a dual line with a dashed identification line to carry the other side. They are not interchangeable, so state the standard your drawing follows.
Dimensions. Weld size to the left of the symbol. Length, and pitch for intermittent welds, to the right.
Tail. Carries anything that does not fit elsewhere: the welding procedure reference, the process, the inspection requirement, a note.
Supplementary symbols. A circle at the elbow means weld all round. A flag means weld in the field. Contour and finish symbols say whether the weld is left as welded, ground flush, or machined.
The five things buyers leave off
1. Weld size. The most common omission. A fillet with no number gets whatever the shop thinks is safe. Fillet weld volume grows with the square of the leg, so the difference between a 5 mm and an 8 mm fillet is roughly two and a half times the weld metal, and a proportional increase in shrinkage.
2. Which side. Drawing a symbol without thinking about arrow side and other side produces joints welded on both sides when one was enough, or one side when both were needed.
3. Length and spacing. Continuous welds are the default when nothing is said. On a long, lightly loaded joint an intermittent weld, say 50 mm of weld every 200 mm, uses a quarter of the metal and distorts far less. If your application permits intermittent welds, say so, because the shop will not assume it.
4. Contour and finish. “Ground flush” and “as welded” are different prices. A weld under a machined face or a mating surface has to be dressed, and if the drawing does not say so, it will not be.
5. Whether tack welds and temporary attachments remain. Lifting lugs, strongbacks and run-off tabs help the shop build the part. If they must be removed and the area dressed flush, that is a line item, and it belongs on the drawing rather than in an email after the fact.
Do not weld everything all round
The all round circle is quick to draw and expensive to make. It commits the shop to welding faces the part does not need welded, including ones in awkward positions, and it puts heat everywhere.
Use it where the joint genuinely needs to be sealed or fully attached. Elsewhere specify the welds you want, on the sides you want them.
Where weld symbols meet GD&T
Weld symbols say what the joint is. They do not say how straight, how flat or how accurately positioned the finished structure has to be. That is a separate language and a separate set of callouts, covered in the GD&T on weldments guide.
The mistake to avoid is trying to control geometry with weld symbols, or trying to control the joint with a general tolerance note. They do different jobs and a weldment drawing needs both.
A short drawing checklist
Before the drawing leaves your desk:
- Every joint has a weld symbol, or a general note that covers the ones without.
- Every fillet has a size.
- The standard is named, AWS A2.4 or ISO 2553, so arrow side convention is unambiguous.
- Leg or throat is stated, not assumed.
- Intermittent welds are used where the loading allows them.
- Welds under machined faces are marked to be dressed.
- The weld quality level and the inspection scope are stated, per joint where they vary.
A drawing that clears that list gets quotes you can compare, because every shop is pricing the same part.
Send your marked up drawing and we will match it with shops that read it the way you meant it.
Frequently asked questions
What happens if my drawing has no weld symbols?
The shop decides the weld type and size for you, and it will decide conservatively because it carries the risk. You get more weld metal than you needed, more distortion and a higher price, and none of it is the fabricator's fault.
Which side of the reference line is the arrow side?
In the AWS convention the symbol below the reference line applies to the arrow side, the joint the arrow points at. The symbol above the line applies to the other side. The ISO convention uses a dashed identification line instead, so state which standard your drawing follows.
Should I specify weld size in leg length or throat?
Either, as long as the drawing says which. Leg length is the common convention for fillet welds on AWS drawings. ISO drawings often use a letter prefix, z for leg and a for throat. Mixing them silently is how a joint ends up undersized by about 30 per cent.
Need a quote for this part?
Send the drawing. We match you with up to 3 shops that weld and machine it in house, and we reply within 24 business hours.
Get matched with a weldment shop