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TIG Cup & Stick-Out Sizing

Calculate the exact maximum tungsten stick-out and recommended argon flow rate for any TIG gas cup number and joint type using the 1/16-inch rule.

Cup Configuration

Cup ID = Number × 1/16". Each number = 1/16" inside diameter.

Joint geometry determines how close the cup must be held — outside corners need maximum gas blanket coverage.

Cup Profile

Max Tungsten Stick-Out

0.438"

Butt Joint — 1× Cup ID

Cup ID

7/16"

0.4375" actual

Argon Flow

14 CFH

Cup # × 2 baseline

Joint Factor

1×

Stick-out multiplier

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What is TIG Welding: Gas Coverage, Cup Selection & Electrode Geometry?

In TIG (GTAW) welding, the gas cup controls two critical variables: the diameter of the inert gas shielding blanket and the physical maximum protrusion of the tungsten electrode. Too much stick-out exposes the hot tungsten and puddle to atmosphere (grey/black contamination). Too little makes it impossible to see the puddle or reach tight joints.

Mathematical Foundation

Cup Inside Diameter (The 1/16" Rule)
ID=N×116ID = N \times \frac{1}{16}
IDID= Inside diameter of the gas cup in inches
NN= Cup number (e.g., #7 = 7/16" = 0.4375" ID)
Maximum Tungsten Stick-Out
Smax=ID×MjointS_{max} = ID \times M_{joint}
SmaxS_{max}= Maximum safe tungsten protrusion past the cup
MjointM_{joint}= Joint multiplier: Fillet = 1.5×, Butt = 1.0×, Outside Corner = 0.75×
Baseline Argon Flow
QCFH=N×2Q_{CFH} = N \times 2
QQ= Shielding gas flow rate in CFH
NN= Cup number — larger cups need more gas volume for coverage

Laws & Principles

  • The 1/16" Rule: Every cup number = 1/16-inch of inside diameter. #4 = 4/16 = 1/4". #8 = 8/16 = 1/2". #12 = 12/16 = 3/4". This is a universal AWS and torch manufacturer standard.
  • Joint Geometry Controls Multiplier: Fillets (inside corners) need 1.5× stick-out because the torch must reach into the root. Butt joints = 1.0×. Outside corners = 0.75× because argon wraps around the joint naturally, allowing less protrusion.
  • Gas Lens = Bigger Cup = Better Coverage: A gas lens collet body produces laminar (non-turbulent) gas flow, allowing larger cups (#10-#14) that provide superior shielding at lower flow rates. Always use a gas lens with #8 or larger cups.
  • The 2× Flow Rule: Baseline CFH = cup number × 2. A #8 cup = 16 CFH. Outdoors in wind, increase by 50%. With a gas lens, you can often reduce by 20%.

Step-by-Step Example Walkthrough

" A pipe welder TIG-welds a stainless root pass on 2-inch Sch 40 pipe (butt joint) using a #8 cup. "

  1. 1. Cup ID: #8 × 1/16 = 8/16 = 0.500 inches.
  2. 2. Joint multiplier: Butt joint = 1.0×.
  3. 3. Max stick-out: 0.500 × 1.0 = 0.500 inches.
  4. 4. Gas flow: #8 × 2 = 16 CFH argon.
Final Result: Set tungsten protrusion to no more than 1/2 inch and open the argon flowmeter to 16 CFH for contamination-free coverage.

Quick Answer: How Far Should the Tungsten Stick Out of a TIG Cup?

Multiply the cup's ID by the joint multiplier. The cup ID = cup number × 1/16". For a #8 cup on a butt joint: ID = 1/2", multiplier = 1.0×, so max stick-out is 1/2 inch. For a fillet (inside corner), multiply by 1.5× = 3/4 inch. Set argon flow to cup # × 2 CFH (e.g., #8 = 16 CFH). This calculator handles every cup size and joint geometry instantly.

TIG Cup Quick Reference

Cup # Cup ID Butt (1.0×) Fillet (1.5×) Gas Flow
#41/4"1/4"3/8"8 CFH
#55/16"5/16"15/32"10 CFH
#63/8"3/8"9/16"12 CFH
#77/16"7/16"21/32"14 CFH
#81/2"1/2"3/4"16 CFH
#105/8"5/8"15/16"20 CFH
#123/4"3/4"1-1/8"24 CFH

#10 and larger cups require gas lens collet bodies for proper laminar flow. Without a gas lens, large cups create turbulent gas patterns that suck in atmosphere at the edges.

TIG Cup & Stick-Out Failures

The Excessive Stick-Out

A welder sets a #6 cup with 1 inch of tungsten stick-out to reach a deep fillet on a stainless header. The cup's ID is only 3/8 inch — max stick-out for a fillet is 9/16 inch. At 1 inch, the tungsten is completely outside the argon shielding envelope. The puddle turns grey-brown within 2 seconds. The welder tries cranking gas to 35 CFH, but the turbulence makes it worse. The correct solution: upgrade to a #10 cup with gas lens. Now ID = 5/8", fillet stick-out = 15/16", and 20 CFH provides crystal-clear shielding with room to spare.

The Gas Lens Upgrade

A food-grade stainless fabrication shop runs #7 standard cups at 20 CFH. Weld quality is marginal — occasional light straw discoloration on the toes. They switch to #12 gas lens cups. Now the shielding blanket is 3/4-inch diameter with perfectly laminar flow. At the same 20 CFH (even slightly less than the #12's baseline of 24), the welds are consistently bright silver with zero discoloration. The gas lens pays for itself in reduced rework within a week. Bonus: the longer stick-out (3/4" on butt joints) gives much better visibility of the root on pipe welding.

Pro Tips for TIG Cup Selection

Do This

  • ✓Use a gas lens for ALL stainless and titanium work. These materials are extremely sensitive to atmospheric contamination. Even minor oxygen exposure causes discoloration (straw → blue → grey) that weakens the weld and fails visual inspection on food-grade, pharmaceutical, and aerospace work. A gas lens + #10-#12 cup is the minimum standard for quality stainless TIG.
  • ✓Start with the 2× flow rule, then adjust by sound. Set flow to cup # × 2. If you hear a hissing turbulence from the cup, reduce flow slightly until it's silent. Turbulent gas flow actually pulls in atmosphere at the edges — more gas can mean WORSE coverage without a gas lens.

Avoid This

  • ✗Don't crank gas flow to compensate for excessive stick-out. If your tungsten extends past the shielding envelope, more gas won't help — it creates turbulence that pulls in MORE atmosphere. The fix is always a larger cup (with gas lens) or reducing stick-out length, never blasting more argon.
  • ✗Don't use #10+ cups without a gas lens body. Standard collet bodies create turbulent gas flow through large cups. The argon swirls and creates vortexes at the edges that suck in atmosphere. A gas lens has layered stainless mesh screens that produce perfectly laminar flow, making large cups effective. Without it, a #12 cup is worse than a #8.

Frequently Asked Questions

What is a gas lens and why does it matter?

A gas lens is a collet body with layered stainless steel mesh screens that straighten gas flow into a laminar (non-turbulent) column. Without it, gas exits the cup in chaotic swirls that lose shielding effectiveness quickly. With a gas lens, the shielding envelope stays coherent much further from the cup, allowing larger cups (+3-4 sizes), longer stick-out, lower gas flow, and dramatically better weld color on stainless and titanium.

Why does the fillet joint allow more stick-out than a butt joint?

In a fillet (inside corner), the two plates act as walls that contain the shielding gas in the joint root — like a natural channel. This containment effect extends the effective shielding distance beyond what the cup alone provides. On an outside corner, gas spills off the edge immediately, requiring the tungsten to stay closer to the cup. The multipliers quantify this containment effect: 1.5× for fillets (joints hold gas), 1.0× for butts (flat, neutral), 0.75× for outside corners (gas falls off).

What color should a TIG weld be?

On stainless steel: bright silver = perfect shielding. Light straw/gold = marginal (acceptable on structural, not on food-grade). Blue/purple = poor shielding — the weld is weakened. Grey/black = severe atmospheric contamination — grind and re-weld. On carbon steel, color is less diagnostic because the oxide layer forms naturally, but excessive blue/black still indicates poor coverage. On titanium: anything other than bright silver means the weld is contaminated and must be removed.

Can I use too much shielding gas?

Yes — this is one of the most counterintuitive facts in TIG welding. Excessive gas flow (>30 CFH on a #8 cup) creates turbulence that draws ambient air INTO the shielding column through a venturi effect. The result looks identical to insufficient gas — discolored welds, porosity, and contamination. If your flow rate seems adequate but welds are still contaminated, try REDUCING flow by 5 CFH. The optimal flow is the lowest rate that produces silent, laminar coverage.

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