Single-J butt weld
Applied to joint
Butt joint — plates aligned end to end
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Equipment for groove welds
MIG and TIG machines suited for groove weld preparations on plate.
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Description
A butt weld where only one member receives a J-shaped (radiused) preparation while the other remains square. The arrow points to the prepared member. Essentially half a U-prep.
In plain English
One plate gets the curved U-style prep, the other stays square. Think of it as the single-bevel equivalent but with a radius instead of a straight bevel. The arrow on the symbol must point to the plate that gets machined. Less filler than a single-bevel on thick plate, but the machining cost is higher. Used when one member is fixed or too awkward to prep, and you want the filler savings of a U on the member you can access.
Symbol position
J symbol on the reference line. Arrow (often broken) points to the prepared member.
Size notation
Root radius, groove angle, root face, and root gap dimensioned.
Notation examples
Same broken-arrow convention difference as single-bevel: ISO uses broken arrow more consistently to indicate the prepared member.
Broken arrow used when needed to indicate which member is prepared.
Broken arrow convention per ISO System A. Root radius 'r' and root face 'c' dimensioned.
Common uses
- T-joints on thick plate
- Joints where only one member can be machined
- Heavy corner joints
- Repair welds with single-side access on thick sections
