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16.7 Dimensions in The Weld Symbol

Cameron Kjeldgaard

Fillet Welds

Fillet weld symbol with the dimensions labeled. A horizontal line, the reference line, with an arrowed line branching up and to the left at about an 80 degree angle. A right triangle is affixed below the reference line, indicating a fillet weld. The number ¼ appears to the left of the right triangle and is marked Size. The numbers 2-6 appear to the right of the triangle. Annotation on the drawing marks 2 as the weld length and 6 as the pitch.
Figure 16.34. Intermittent Fillet Weld Symbol / Photo Credit: Cameron Kjeldgaard, CC BY 4.0

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.

A two view drawing of a T-joint. The left hand view shows the joint in cross section with an intermittent fillet weld symbol. The cross section of the T-Joint is two rectangles, one lays flat while the other is centered and perpendicular to the other. The weld symbol shows the reference line with 2-5 printed above the line and 2-5 below the line, indicating that each weld length is 2, and each pitch is 5. The view on the right shows the joint from a top down view with welds illustrated to show the significance of the symbol. The illustration shows that on the left edge of the plate is a weld of 2”, there is a break for 3” and then another weld of 2”, a final break of 3” and a weld of 2” that reaches the edge of the plate. At the base of the illustration, there is a measurement that shows there is 5” between the center of each weld.
Figure 16.35. The Significance Of The “Length And Pitch” Elements Of The Weld Symbol Used In Intermittent Fillet Welding / Photo Credit: Nicholas Malara, CC BY 4.0

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.

Two weld symbols. The left symbol is for chain intermittent weld. It shows a reference line shows ¼ next to two right angle triangles that are stacked directly over each other, and 2-6 as the length and pitch of the weld. The symbol on the right is for a staggered intermittent weld. It shows the reference line with ¼ to the left of a right triangle on the top of the line, and 2-6 for the length and pitch. At the bottom of the reference line ¼ is also shown to the left of the triangle, however the triangle is staggered to the left and so that the left side of the triangle above the reference line meets the center of the top line of the triangle on the bottom. The length and pitch are still marked 2-6.
Figure 16.36. Chain and Staggered Fillet Weld Symbols / Photo Credit: Cameron Kjeldgaard, CC BY 4.0

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

A diagram of a V groove weld joint with applicable dimensions labeled and a corresponding weld symbol. The illustration shows a V-Groove with a 60 degree angle going down ¾ before becoming straight for ¼. The weld symbol shows a reference line that is marked on the bottom with ¾ to the left of an upside down V-shape that includes the measurements ¼ and 60 degrees written within the two lines of the V-shape. The arrow line points to the right-hand side of the V-Groove.
Figure 16.37. V Groove Weld Symbol / Photo Credit: Cameron Kjeldgaard, CC BY 4.0

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.

Groove welding symbol with two sizes shown, the sizes shown are ¾ and ⅞.
Figure 16.38. Groove Weld Sizes / Photo Credit: Cameron Kjeldgaard, CC BY 4.0

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.

A diagram of a groove weld with a backing bar and corresponding welding symbol. The diagram shows two rectangles with a slope cut into the side of each one, which is the V groove. A rectangle underneath the two pieces is marked backing bar. The weld symbol shows a reference line with a V groove marking below the reference line the measurement ¼ is within the upside down V-shape. A rectangle, representing the backing bar is on top of the reference line.
Figure 16.39. V Groove with Backing Bar / Photo Credit: Cameron Kjeldgaard, CC BY 4.0

Groove welds with root openings often use backing bars. Root openings allow for complete penetration of the weld joint, and the backing bar prevents the molten weld metal from falling out of the root side of the joint. The backing symbol is a small rectangle and will be placed on the opposite side of the reference line from the groove symbol. In some cases the letter “R” can be present within the backing bar symbol, this indicates removal of the backing bar once welding is complete.

Plug and Slot Welds

A plug welding symbol with common dimensions for plug welds. In this symbol the bottom of the reference line includes a rectangle with the diameter symbol and 1 to the left of the rectangle. ½ is written inside of the rectangle, 60 degrees appears under the rectangle and the number 5 in parenthesis appears below that.
Figure 16.40. Plug Weld Symbol / Photo Credit: Cameron Kjeldgaard, CC BY 4.0

The plug weld symbol is a simple rectangle, and can be confused with the backing bar symbol. However, if there is no groove symbol on the other side of the reference line it is safe to assume a plug weld is being called for.

The diameter of the hole the plug weld is going in is shown to the left of the plug weld symbol. A number inside the symbol itself indicates the depth to which the plug should be filled with weld metal. If the hole is to be countersunk the degree of the countersink will be directly below (or above) the weld symbol. It is very common for multiple plug welds to be used when joining two parts. The number of required welds will appear in parenthesis directly below (or above) the angle of countersink. When multiple plug welds are needed their locations will need to be detailed on the print.

Slot welding symbols use the same rectangular weld symbol. But in the case of slot welds the diameter symbol will not be present to the left of the symbol, just a number indicating the width of the slot. The length of the slot will appear to the right of the symbol.

Attributions

  1. Figure 16.34: Intermittent Fillet Weld Symbol by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
  2. Figure 16.35: The Significance Of The “Length And Pitch” Elements Of The Weld Symbol Used In Intermittent Fillet Welding. by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0
  3. Figure 16.36: Chain and Staggered Fillet Weld Symbols by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
  4. Figure 16.37: V Groove Weld Symbol by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
  5. Figure 16.38: Groove Weld Sizes by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
  6. Figure 16.39: V Groove with Backing Bar by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
  7. Figure 16.40: Plug Weld Symbol by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
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Introduction to Welding Copyright © by Washington State Board for Community and Technical Colleges is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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