16.7 Dimensions in The Weld Symbol
Cameron Kjeldgaard
Fillet Welds
Fillet welds involve fewer dimensions in the welding symbol than groove welds. In the simplest case the fillet weld symbol and size will be present, the weld size is always to the left of the symbol, the same is true for groove welds. If the weld size is the only dimension present then it is a continuous weld and should go the entire length of the weld joint.
The two dimensions to the right of the weld symbol are length and pitch. These are used for intermittent welds, sometimes called stitch welds. It is often unnecessary to weld the entire length of long weld joints. The above example calls for a 2 inch long weld, spaced every 6 inches. The spacing is called the pitch, and is measured from the center of one weld to the center of the next weld. We can see this illustrated in the example below, where the weld symbol calls for 2 inch long welds on a 5 inch pitch.
Intermittent welds may also be chained or staggered. The example directly above shows chained welds, that is the welds on each side of the joint are lined up with each other. If the welds are staggered then the welds on one side of the joint are offset from the welds on the other. It is best to offset the welds ½ the required pitch, so that welds on one side of the joint are centered between the welds on the other side. A slight offset of the weld symbols will indicate the welds should be staggered as seen below.
If there is only one number to the right of the welding symbol it is for the length of the weld. As a pitch will never be given without a length also being given, but a length may be given without a pitch. If only a length is given the detailer may use dimension and extension lines to indicate where the weld should be located on the joint. If this is not done it is best practice to center the weld on the joint.
Groove Welds
Groove welding symbols can be more involved and complex than fillet welding symbols. Just like with the fillet weld the size is to the left of the weld symbol. Groove weld size is a reference to the depth of the groove cut into the material. If no size is shown, then assume the groove depth is the same as the material thickness, so the groove is cut all the way through the material with no root face. If there is a root opening it will be shown directly below the weld symbol, with the groove angle directly below that. If the weld symbol is on top of the reference line the root opening and groove angle with be shown in an ascending order.
It is not always the case, but groove welding symbols may have two sizes shown, once again to the left of the weld symbol. The size not in parentheses once again references the depth of the groove prior to welding. The size shown in parenthesis is the required size of the finished weld. The weld size is typically larger than groove depth, and indicates a required amount of penetration into the joint root.
Groove welds with root openings often use backing bars. R