What's inside
As an Amazon Associate I earn from qualifying purchases. This post may contain affiliate links at no extra cost to you.
What makes this joint different
A stainless steel lap joint puts one piece of metal over another, with a fillet weld along an edge. It is a practical joint for thin sheet, patches and brackets, but the overlap can trap moisture or contaminants. That matters on stainless: a weld that looks sound can still leave a crevice that corrodes in service.
Before welding, check whether a lap joint suits the job. If both sides must be easy to clean, or the assembly will see food, chemicals or standing water, a butt joint or a fully sealed design may be better. For a general-purpose indoor bracket, a lap joint is often a simple, strong choice.
Tools and materials
Use a DC TIG welder with a foot pedal or torch amperage control, a 2% lanthanated or ceriated tungsten, argon shielding gas, stainless filler, clamps and a stainless-only wire brush. A gas lens can improve shielding, especially if access is awkward. A dedicated TIG torch gas-lens kit is useful, but not essential for a straightforward joint with good torch access.
For common 304 stainless, ER308L filler is a typical match; ER316L is commonly used with 316 base metal. Confirm the material grade and filler recommendation for the actual service conditions. Do not use a carbon-steel brush or grinding disc on stainless. Embedded iron can rust and stain the surface.
Wear a properly rated welding helmet, gloves and flame-resistant clothing. TIG arcs are bright even at modest amperage. A TIG-capable auto-darkening helmet should reliably detect low-amperage starts; check its stated operating range rather than choosing by shade number alone.
Fit-up and cleaning
Remove oil, paint, adhesive and marker from the weld area with a suitable cleaner, then let the surface dry fully. Degreasing comes before abrasion: grinding through oil can spread contamination. Use a clean stainless brush or dedicated abrasive to remove oxide where needed.
Set the overlap to suit the design, commonly around one to two times the thinner sheet’s thickness. That is a starting point, not a strength calculation. Clamp the pieces so they sit flat and the edge is accessible. A gap invites burn-through and inconsistent fusion; aim for close contact, ideally no more than about 0.5 mm on thin sheet. Tack at both ends and near the middle, then recheck alignment.
Stainless expands and distorts readily. Short, balanced weld sections and firm clamping help keep the joint flat. Do not clamp so aggressively that you prevent the assembly from moving at all; plan the weld sequence to limit heat buildup.
Settings and joint options
Use DC electrode negative (DCEN) and pure argon, typically around 7–12 L/min (15–25 cubic feet per hour) with a standard cup in a draft-free space. Too much gas flow can create turbulence and pull air into the shield. Start with a sharp tungsten point and a stick-out of roughly 3–5 mm, adjusted to the cup and access.
| Material thickness | Starting current range | Practical note |
|---|---|---|
| 0.8–1.0 mm (20–18 gauge) | 25–45 A | Use a small, quick puddle; pedal control helps prevent burn-through. |
| 1.2–1.6 mm (16–14 gauge) | 40–70 A | Moderate travel speed and small filler additions usually work well. |
| 2.0–3.0 mm (12–11 gauge) | 60–110 A | More current may be needed, depending on joint mass and position. |
These are starting points, not machine prescriptions. Fit-up, torch angle, joint mass and operator speed all affect the setting. Make a test weld on matching scrap and adjust until the puddle forms promptly without undercutting or burning through.
A continuous fillet seals the edge better than intermittent welds, but puts more heat into the panel. Intermittent welds can reduce distortion on non-sealing structural work, though the unwelded gaps may hold dirt or moisture. Choose based on the service environment, not appearance alone.
TIG welding the lap joint
Position the torch so the arc reaches both pieces at the joint edge. Hold it at about 10–15 degrees from vertical, with a short arc—roughly 1–2 mm. Start the puddle on the thicker or heat-sinking side if the pieces differ in thickness, then wash the puddle across both surfaces. A fillet that sits only on the top sheet may look neat but have little fusion to the lower piece.
Add small amounts of filler at the leading edge of the puddle. For thin sheet, try a 1.0 mm rod; thicker work may suit 1.6 mm. Keep the rod tip inside the argon shield between additions. Move steadily, keeping the bead small and consistent rather than dwelling to build height. If the puddle grows too wide, reduce current with the pedal or stop briefly and let the metal cool.
At the end, taper off current and hold the torch in place briefly while shielding gas continues. Many TIG machines provide post-flow; roughly 5–10 seconds is a useful starting range for a small stainless weld. Let the work cool naturally. Quenching can distort the joint and does not improve the weld.
Inspect and correct problems
A sound fillet should be continuous where required, with a smooth transition onto both sheets. Look for undercut, pinholes, cracks, obvious lack of fusion and heavy blue or black oxidation. A small silver or light-straw weld is a better sign of heat control than a dark, sugared surface, but color alone does not prove strength.
Common faults have direct fixes. Burn-through usually means too much heat, too long a pause or poor fit-up; reduce amperage, move faster and close the gap. A tall bead with poor tie-in suggests insufficient heat or an overly fast filler addition; improve puddle wetting on both pieces. A contaminated, porous weld calls for cleaner metal, steady gas coverage and a tungsten that has not touched the puddle. If the tungsten is contaminated, stop, regrind it and resume on clean material.
For critical or load-bearing work, do not rely on a visual check or a generic amperage chart. Follow the applicable design and welding requirements, and have the joint inspected or tested as the application demands.