Small weld, often 1/2 to 1 inch long, placed at intervals during fit-up to fix parts in position. Tacks that get consumed into the final weld must be made by a qualified welder with the proper filler and preheat, and their ends are usually ground or feathered so the root can tie in. Cracked or poorly fused tacks are removed, since welding over them traps defects.
Four tack welds at twelve, three, six and nine, feather them so the root ties in clean.
Also heard as
- tack
- tacks
- tacking
Related terms
Fit-up
Positioning and holding parts for welding with the right gaps, alignment and clean bevels.
Feather
To grind the start, stop or tack of a weld to a thin taper so the next bead can tie in smoothly.
Root pass
The first weld pass in a joint, laid at the root, which sets the quality of everything above it.
Preheat
Heating base metal before welding to slow cooling and drive off moisture, preventing hydrogen cracks.