J-Groove Weld Symbol
The J-groove weld symbol is a vertical leg on the left with a curved leg beside it, like a J, standing on the reference line. Only one member is prepared, with a radiused groove, and an arrow break points at it when needed. Below the line is arrow side, above is other side; sizes left, root opening inside and groove angle beyond.
How to read the j-groove weld symbol
A J-groove is half of a U: one member is machined with a rounded-bottom groove, the other stays square. It is used on T-joints and butt joints in thick material where only one part can, or should, be prepared.
As with the bevel, the perpendicular leg is always on the left and an arrow break shows which member is prepared. Below the line: arrow side; above: other side; on both sides: double-J.
What each dimension position means
| Position | Meaning |
|---|---|
| Left (S) | Depth of groove preparation. |
| Left, in parentheses (E) | Groove weld size. |
| Inside (R) | Root opening. |
| Beyond (A) | Groove angle of the prepared side. |
| Arrow break | Points to the member that receives the J preparation. |
Example callout, read aloud
“On the arrow side, machine a J-groove in the member the arrow points to, with a 25-degree groove angle, 1/2 inch deep and a 1/8-inch root opening, and weld to a groove weld size of 1/2 inch.”
Example: reading the callout piece by piece
- J below the line: arrow side.
- 25° beyond: groove angle of the J.
- 1/8 inside: root opening.
- 1/2(1/2): preparation and weld size 1/2 inch.
Result: On the arrow side, machine a J-groove in the member the arrow points to, with a 25-degree groove angle, 1/2 inch deep and a 1/8-inch root opening, and weld to a groove weld size of 1/2 inch.
When it is used
- Thick T-joints needing full strength, where a bevel would need too much filler.
- Butt joints between a thick part that can be machined and one that cannot.
- Double-J on very thick T-joints welded from both sides.
Common mistakes
- Preparing both members. A J prepares one member. Two prepared members would be a U.
- Ignoring the arrow break. It tells you which part to machine.
- Drawing the vertical leg on the right. The perpendicular leg is always on the left.
- Expecting the radius on the symbol. Groove radius is given in a detail or the tail.
Related weld symbols
- U-groove weld: A U-groove prepares both members.
- Bevel groove weld: A bevel is the straight-sided one-member groove.
- Fillet weld: A fillet may be added over a J on a T-joint.
- V-groove weld: A V prepares both members with straight sides.
- Back and backing weld: A back weld can complete the root of a single J.
Every weld symbol page: welding symbols chart
Calculators and further reading
Frequently asked questions
What is the difference between a J-groove and a U-groove?
A J prepares one member with a rounded groove; a U prepares both.
Which member gets the J?
The one the broken arrow points to. Without a break, either member may be prepared.
What does a J on both sides of the line mean?
A double-J: the member is prepared from both sides and welded from both sides.
Why use a J instead of a bevel?
On thick sections the J needs less weld metal than a bevel of the same depth.
Sources
- AWS A2.4 Standard Symbols for Welding, Brazing, and Nondestructive Examination, American Welding Society
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