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Adding filler smoothly is mostly a timing and distance problem: keep the tungsten steady, hold a short arc, and feed small amounts of rod into the edge of the molten pool. If the rod gets too far ahead, the bead piles up; if it falls behind, the weld can underfill or the base metal can burn through. A little practice on clean scrap helps more than changing equipment.
Choose the right filler rod
Match the filler to the base metal and the job. For common mild-steel work, ER70S-2 is a widely used choice; ER70S-6 can suit steel with slightly more surface contamination, but neither makes dirty or rusty metal a good welding surface. For aluminum, use a compatible aluminum filler such as 4043 or 5356 as specified for the alloy and service. If the part is load-bearing, pressure-containing, or otherwise safety-critical, follow the applicable welding procedure rather than choosing by convenience.
Rod diameter should be close to the thickness of the material and the size of the pool. A 1/16-inch rod is handy for thin sheet and small pools; 3/32-inch is a common all-purpose size for moderate work. A rod that is too large chills a small pool and is awkward to feed. One that is too small may melt back quickly and make your feed inconsistent.
Prepare the joint and setup
Remove oil, paint, rust, mill scale, and oxide from the joint and the filler rod. Use a brush reserved for the metal you are welding, especially on aluminum, where a dedicated stainless-steel brush helps avoid contamination. Fit the pieces so the joint gap is consistent. A changing gap forces you to change how much filler you add and how fast you move.
Set the machine for the material, thickness, and joint, then make a short test bead on matching scrap. For thin steel, excessive amperage or a slow travel speed can open a hole before you have time to add filler. Too little heat can leave a tall, cold bead with poor tie-in at the edges. A foot pedal or fingertip amperage control is useful when the joint changes thickness, but fixed-current machines are fine for steady, repeatable work. If you are buying a first TIG setup, compare TIG welding foot pedals against the cost of a basic machine with fixed output; control is helpful, not a substitute for practice.
Wear a correctly rated welding helmet, gloves, and protective clothing. TIG arcs are bright, and the workpiece stays hot after the arc stops. A stable hand rest and clear view of the joint matter too: if you cannot see the pool, filler timing becomes guesswork.
Set your hand position and rod angle
Hold the torch so the tungsten points into the direction of travel, typically with the torch tilted about 10 to 20 degrees from vertical. Keep the tungsten close to the work without touching it; a short arc, often around 1/16 to 1/8 inch, gives better control and a narrower heat-affected area. Touching the tungsten with the rod contaminates it. If that happens, stop and regrind the tungsten before continuing.
Hold the filler rod at a shallow angle, roughly 10 to 20 degrees above the work, and bring its tip to the leading edge of the pool. Keep the rod under the shielding gas as you feed it. Pulling the rod tip out into the air while hot can oxidize it, leaving contamination to enter the weld. The exact angles vary with access and joint shape, so prioritize a clear view and steady hands over a rigid measurement.
Feed small amounts, steadily
Start the arc and form a small, shiny pool that wets both sides of the joint. Dip the rod tip into the front edge of the pool, then withdraw it slightly without lifting it out of the shielding gas. Repeat in a steady rhythm while moving the torch forward. Think of the motion as “dip, advance, dip,” not as pushing the rod continuously through the pool.
Use only enough filler to maintain the bead profile and bridge the joint. On a narrow bead, a small dip may be enough; a large glob can cool the pool and leave a lumpy surface. Keep the torch moving at a pace that lets the pool stay controlled. If the bead grows too tall, reduce the amount of filler per dip or increase travel speed slightly. If it is narrow and underfilled, add a little more filler or slow down, while watching for excess heat.
Common filler-feeding problems
| What you see | Likely cause | What to change |
|---|---|---|
| Tall, rope-like bead | Too much filler, too little heat, or slow travel | Feed smaller dips; check current and move steadily |
| Undercut or a thin bead edge | Fast travel, insufficient filler, or excessive heat | Add filler consistently and adjust travel or amperage |
| Black, sooty-looking weld | Contamination or poor shielding gas coverage | Clean the metal; check gas flow, drafts, and torch position |
| Tungsten turns dirty or unstable | Rod or pool touched the tungsten | Stop, regrind the tungsten, and restart on clean material |
If the pool looks turbulent or the weld is discolored, do not simply turn up the gas. Excessive flow can create turbulence that draws air into the shielding zone. Check the torch cup, gas lens if fitted, connections, and nearby drafts. A TIG gas lens kit can improve gas coverage on some setups, but a sound cup and correct gas flow are often all a beginner needs.
Practice and inspect the bead
Practice on flat scrap of the same material and thickness before welding the actual part. Make short beads, then check whether both edges fused and whether the bead is reasonably even. A smooth-looking top is not proof of a sound weld: a tall bead may have poor fusion underneath. For thin sheet, inspect the back for signs of burn-through or a continuous root bead where the joint calls for it.
Adjust one variable at a time—filler amount, travel speed, torch angle, or amperage—so you can identify what changed the result. If the joint is too awkward to see or reach, reposition the work rather than feeding rod blindly. On critical work, use the specified procedure and inspection method; a visually tidy practice bead is not qualification.