Finishing Skills: Crater Fill, Stop/Restart Control, and Bead Blending for Clean Results

Why “finishing” matters: the crater is a crack starter

In TIG, the last few millimeters of a weld determine whether the bead looks professional and whether it survives service. When you stop abruptly, the molten puddle shrinks as it cools and can leave a concave crater. That crater is a stress concentrator and can form a crater crack (often a tiny star-shaped or centerline crack at the end of the bead). Finishing skills are the habits that prevent that: tapering heat, adding the right final filler, and keeping shielding on the hot metal until it cools enough to resist oxidation.

What a “good finish” looks like

• End of bead is slightly crowned or at least flush—not a deep divot.
• Ripple pattern continues smoothly into the termination (no sudden wide/skinny ripples).
• No visible end crack under bright light.
• Minimal oxidation at the end (especially on stainless): color stays consistent with the rest of the bead, and the stop area is not dull/gray and crusty.

Crater fill technique: taper amperage, add final filler, keep shielding

Concept: shrinkage happens after you stop adding heat

The puddle contracts as it solidifies. If the puddle is left thin at the end, it can tear itself as it shrinks. Your goal is to leave the end slightly “overfilled” while reducing heat so the puddle freezes without collapsing.

Step-by-step: ending a bead without crater cracking

1. Plan the last 10–15 mm. As you approach the end, slow down slightly and prepare to reduce amperage. Avoid “rushing the exit.”
2. Taper amperage gradually. Use your control method (pedal or fingertip control) to ramp down over about 1–2 seconds rather than cutting off. The idea is to reduce puddle size while keeping it fluid enough to accept a final dab.
3. Add final filler as you taper. Feed one or two small dabs while the puddle is still wet. Think: less heat + a touch more metal. This leaves a gently crowned end instead of a crater.
4. Pause briefly to let it freeze under gas. Hold the torch steady over the end as the puddle solidifies. Don’t lift away immediately; keep the tungsten in position so shielding stays centered.
5. Maintain post-flow coverage during cooldown. Keep the torch in place until the glow is gone and the surface looks “dead” (no visible shimmering heat). This is especially important on stainless and titanium, but it also improves mild steel appearance and protects the tungsten from oxidation.

Two common crater-fill patterns (choose one and practice it)

• “Taper + dab” finish: Reduce amperage while adding 1–3 small dabs, then hold position for freeze and post-flow.
• “Backstep” finish: At the end, briefly step back 3–6 mm over the previous ripples while tapering amperage and adding a final dab. This blends the termination into the bead and helps hide the stop point.

Quality checkpoints at the end of the weld

• Crater shape: If you can catch a fingernail in the end divot, it’s usually too concave.
• End crack check: Use a bright light at a low angle; rotate the coupon. Tiny cracks often show as a sharp line right at the center of the crater.
• Shielding evidence: A sudden dull/sooty end (mild steel) or chalky gray end (stainless) often indicates you pulled away too soon or had inadequate post-flow coverage at the termination.

Stop/restart control: making interruptions invisible

Concept: restarts fail for two reasons

• Contamination at the restart area: Oxide, soot, or a dirty filler tip gets trapped when you re-melt.
• Heat mismatch: If you restart too cold, you pile metal and create a lump; too hot, you wash out the edge and create a wide, flat spot. Either way, the ripple pattern breaks and the restart becomes obvious.

Step-by-step: clean, re-establish the puddle, blend ripples

1. Stop correctly first (crater fill). A clean stop makes the restart easier. Avoid leaving a deep crater.
2. Let it cool enough to handle the restart cleanly. If it’s still extremely hot, you’ll fight oxidation and puddle instability. If you must restart hot, be extra strict about shielding coverage and cleanliness.
3. Clean the restart zone. Mechanically clean 10–20 mm around the stop area. Your goal is bright, uniform metal with no dark film. Also clip or re-prep the filler rod tip if it’s oxidized or dirty.
4. Position for overlap. Start the arc slightly behind the end of the previous bead (typically 3–6 mm) so you can re-melt and tie in, then travel forward.
5. Re-establish the puddle before adding filler. Bring the previous bead end back to a shiny, fluid state. Watch for the edges to wet in; don’t rush filler into a half-formed puddle.
6. Add a small “tie-in” dab. Once the puddle is re-established, add a controlled dab to fill any slight crater and to match bead height.
7. Blend the ripple rhythm. Resume your normal travel speed and filler timing. Aim to match the spacing and size of the previous ripples. If your ripples suddenly tighten or spread, adjust speed/amperage until they match.
8. Finish with a crater fill again. Every stop is a potential crack starter; treat the final stop the same way.

Blending tricks for a seamless restart

• Use a short overlap: Overlap enough to fully re-melt the last ripple or two, but not so long that you create a wide “double-heated” zone that looks different.
• Match bead profile: If the restart is taller, reduce filler slightly or increase travel speed; if it’s flatter, add a touch more filler or reduce travel speed while keeping heat consistent.
• Keep the torch centered: A restart that drifts to one side leaves a visible toe line mismatch. Use the previous bead as a visual track.

Bead blending for clean results (when appearance matters)

Concept: blending is controlled remelting, not “scrubbing”

Bead blending means making transitions (starts, stops, tie-ins, and short repairs) look continuous. The goal is to re-melt just enough to unify ripple pattern and bead height without overheating the surrounding area.

Step-by-step: blending a stop/restart line

1. Identify the discontinuity. Look for a visible line, a height step, or a ripple pattern change.
2. Clean the area. Any blending pass over contamination will lock defects in place.
3. Re-melt only the top portion of the bead. Use slightly reduced amperage compared to the original pass. You want the surface to go glossy and fluid without widening the bead dramatically.
4. Add minimal filler (if needed). If there’s a low spot, add tiny dabs; if it’s already high, avoid filler and focus on smoothing.
5. Travel with consistent rhythm. Keep ripple spacing uniform through the blended zone so it doesn’t look like a separate “patch.”
6. End with proper crater fill and post-flow hold.

When to rework instead of blend

• Visible crack at the crater or restart line.
• Porosity exposed at the surface after re-melt.
• Undercut at the toes that remains after a light blending pass.
• Severe oxidation (dull, crusty surface) that suggests shielding loss—clean back to sound metal before attempting a repair pass.

Mini-projects to build finishing and restart skill

These short exercises are designed to make your stops and restarts repeatable. Keep each coupon labeled with settings and notes so you can compare results.

Mini-project 1: “Ten perfect stops” on a flat bead coupon

Goal: Make 10 short beads (25–40 mm each) where every termination is crack-free and visually consistent.

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• Coupon: Flat plate coupon, clean and deburred.
• Task: Weld a short bead, crater fill, hold post-flow. Move over and repeat until you have 10 terminations to inspect.
• Quality criteria: No concave craters; consistent bead height; no end cracks; end color/finish matches the rest of the bead.
• Self-inspection steps: Use angled light to check for crater cracks; compare end ripple spacing to mid-bead; look for a dull end zone indicating you lifted out of shielding too soon.

Mini-project 2: Stop/restart ladder (overlap consistency)

Goal: Make a single bead in 4–6 segments with stops and restarts that are difficult to locate visually.

• Coupon: Flat plate coupon long enough for a 150–200 mm bead.
• Task: Weld 30–40 mm, stop with crater fill. Clean the restart area, then restart with a 3–6 mm overlap. Repeat.
• Quality criteria: Restart lines are not raised or sunken; ripple pattern stays consistent; bead width does not “flare” at restarts.
• Self-inspection steps: Run a fingertip lightly across restarts to feel steps; visually track the toes—any toe jog indicates torch drift; check for tiny pinholes that can appear at restarts if the area wasn’t cleaned.

Mini-project 3: Fillet joint tie-ins (two-direction stops)

Goal: Practice finishing at the end of a fillet where heat builds and access changes.

• Coupon: Simple T-joint or lap joint with a straight run.
• Task: Weld a fillet for 50–75 mm. Stop cleanly. Restart and continue. Focus on keeping the crater filled at the end of each segment without overbuilding the corner.
• Quality criteria: Even leg size; no undercut at either toe; stop/restart blends into the fillet profile; no crater crack at the end of the fillet.
• Self-inspection steps: Look along each toe line for undercut shadows; check the end of the fillet for a centerline crack; verify the final termination is not a sharp notch at the corner.

Mini-project 4: “Blend and match” repair strip (controlled remelt)

Goal: Learn to blend a visible restart without widening the bead.

• Coupon: Flat plate with a bead that intentionally has a noticeable restart (make one on purpose by changing speed slightly).
• Task: Clean, then make a light blending pass over only the restart zone (20–30 mm). Use minimal filler unless there’s a low spot.
• Quality criteria: Restart line becomes difficult to see; bead width remains consistent; no new oxidation or rough surface texture.
• Self-inspection steps: Compare bead width before/after blending; check for a “halo” of discoloration that indicates excess heat; verify the blended zone still has smooth toes and no undercut.

Visual standards: what discoloration and surface cues are telling you

Reading the stop area

Quick self-inspection routine (use after every practice coupon)

1. Light and angle: Shine a bright light across the bead at a low angle to reveal cracks, undercut shadows, and restart lines.
2. Termination check: Inspect every stop for crater concavity and any centerline crack.
3. Restart check: Look for a step in bead height and a change in ripple spacing. If you can immediately point to the restart, it needs refinement.
4. Surface cleanliness: Note any dull, crusty, or heavily discolored areas concentrated at stops/restarts—these are strong clues of shielding loss during cooldown or poor cleaning before restart.
5. Mark rework zones: Use a marker to circle defects and write the suspected cause (e.g., “pulled away early,” “no overlap,” “added filler too soon”).