What's inside
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The Basic Angle for a TIG Fillet Weld
For a standard 90-degree inside fillet weld, start with the TIG torch at approximately a 45-degree work angle. This lets the arc reach both pieces evenly instead of concentrating heat on one side. The torch should point into the corner, with the tungsten centered over the joint root.
That 45-degree figure is a starting point, not a measurement you must hold perfectly. A practical range is usually about 40 to 50 degrees, depending on joint access, material thickness, and the size of the fillet. If the torch is too upright against one plate, the other plate may show poor fusion. If it is aimed too deeply into the corner, the arc can become difficult to control and may wash metal unevenly up one wall.
Keep the tungsten pointed in the direction of travel and use a modest travel angle. For most fillet welds, tilt the torch 10 to 15 degrees from vertical in the direction of travel. This is commonly called a push angle. A slight push helps you see the puddle and keeps the shielding gas ahead of the weld. Excessive angle, such as 25 degrees or more, can disturb shielding and produce a flat, inconsistent bead.
Work Angle Versus Travel Angle
These two angles control different things. The work angle is the torch’s side-to-side angle across the joint. On a 90-degree fillet, it is normally close to 45 degrees. The travel angle is the forward or backward tilt along the weld. It is generally 10 to 15 degrees when pushing the torch.
It helps to picture the tungsten as aiming at the exact corner where the two pieces meet. The torch cup should not be rubbing either plate, and the tungsten should remain centered rather than sweeping from side to side. Hold a short arc—about 1 to 1.5 times the tungsten diameter. With a 3/32-inch tungsten, that means roughly 3/32 to 1/8 inch. A long arc spreads heat, reduces penetration, and makes the bead wider and less predictable.
| Condition | Starting work angle | Typical travel angle | What to watch for |
|---|---|---|---|
| Equal-thickness 90-degree inside fillet | 45 degrees | 10–15 degrees push | Even wetting on both legs |
| One plate substantially thicker | About 40–45 degrees, biased toward the thick plate | 10–15 degrees push | Heat must reach the thicker member |
| Restricted inside corner | 35–45 degrees as access allows | 5–15 degrees | Avoid touching the cup or losing gas coverage |
| Outside corner or lap-style edge joint | Usually 45 degrees, adjusted to the joint shape | 10–15 degrees push | Prevent the arc from favoring one edge |
Adjusting the Angle for Unequal Materials
When the two pieces are different thicknesses, do not automatically keep the torch exactly bisecting the joint. The thicker piece usually needs more heat. Bias the torch slightly toward it, often by 5 to 10 degrees, while still allowing the arc to wash onto the thinner piece.
For example, if a 1/8-inch plate is welded to a 1/4-inch plate, aim slightly more at the 1/4-inch plate. Keep the arc moving and avoid lingering on the thin edge. If the thin piece is melting away, reduce heat, increase travel speed, or direct the arc farther toward the thick member. If the thick plate does not fuse, slow down, add a little amperage, or increase the bias toward it.
Do not solve every fusion problem by changing torch angle. Poor fit-up, mill scale, oil, and an inadequate amperage setting are common causes. TIG requires clean base metal; brush stainless steel with a dedicated stainless brush and remove aluminum oxide with a clean stainless brush before welding.
How Torch Height and Cup Size Change Angle Control
Angle and arc length work together. Raising the torch to reach an awkward corner increases arc length and weakens control. Instead, reposition the work, use a smaller cup, or select a torch setup that fits the joint. A #5 or #6 cup can be useful in tight fillets, while a larger cup gives better gas coverage on open joints but needs more clearance.
A gas lens can make shielding more forgiving, especially when the torch must be held at a less-than-ideal angle. It does not make a bad angle harmless. Excessive tilt can still pull surrounding air into the shielding envelope. If you regularly weld fillets in corners or around tubing, a TIG gas lens and cup kit is a reasonable upgrade, but a standard collet body is adequate for many shop jobs.
Keep the cup close enough for coverage without dragging it. A common starting distance is about 1/8 to 1/4 inch from the work, depending on the cup and gas lens. Use the smallest practical tungsten extension beyond the cup. Too much stickout makes shielding more vulnerable, particularly with argon flow disrupted by a steep travel angle.
Reading the Puddle and Correcting Errors
A correctly positioned torch produces a puddle that wets both plates at nearly the same rate. The bead should tie into each leg without a sharp groove along one side. If one leg is cold and narrow while the other is wide and heavily rippled, adjust the work angle first.
- Cold lap on one wall: Aim the torch slightly toward that wall, slow travel, or increase amperage.
- Undercut at one edge: Reduce the angle favoring that edge, shorten the arc, and avoid excessive amperage or travel speed.
- Burn-through on the thin member: Bias heat toward the thick piece, move faster, reduce amperage, or use pulsing.
- Porosity: Check gas flow, drafts, contamination, torch leaks, and cup coverage before changing angle.
- Bead wandering in the corner: Improve torch support and maintain a consistent short arc instead of weaving.
For most small fillets, avoid a wide side-to-side weave. A steady travel path with a slight pause at each toe is easier to control and usually gives better fusion. If you need a larger fillet, make multiple passes rather than forcing one oversized bead with a steep torch angle.
Tools That Make Fillet Angle Easier
A flexible TIG torch can help when the handle blocks your wrist or forces the tungsten out of position. A standard air-cooled torch is fine for light and intermittent work; a water-cooled torch is more comfortable for high-amperage welding or long sessions. If you are buying a torch for varied fabrication, compare flex-head TIG torches by connector type and amperage rating, not just price.
Use a stable fixture and tack the joint before welding. Even a perfect 45-degree angle cannot compensate for a joint that opens, shifts, or has inconsistent root contact. A simple magnetic or mechanical fixture is useful for steel, but do not rely on magnets near every sensitive setup; a rigid clamp and clean fit-up are often the cheaper, better option.
Wear a properly rated auto-darkening TIG helmet with a clear lens and sufficient low-amperage sensitivity. Seeing the puddle clearly makes it much easier to hold the torch at 45 degrees and correct the angle before a lack-of-fusion defect becomes part of the weld.