Why Torch Anatomy Matters for Clean Welds
In TIG welding, the torch is not just a handle for the electrode—it is a gas delivery system, an electrical contact system, and a precision alignment tool. Clean welds depend on stable arc behavior and consistent shielding gas coverage. Most “mystery contamination” problems trace back to torch consumables that are mismatched, assembled incorrectly, loose, or damaged.
TIG Torch Components and What Each One Does
Torch body (head)
The torch body routes welding current to the tungsten and routes shielding gas to the cup. It also sets the physical angle and access you can achieve. A torch head that is overheated or physically damaged can distort consumable fit, leading to leaks or misalignment.
Collet
The collet is the split sleeve that grips the tungsten. When the back cap is tightened, the collet is pulled into the collet body and clamps the tungsten. A worn collet can clamp unevenly, allowing the tungsten to sit off-center, which often shows up as a wandering arc.
- Key job: center and hold tungsten securely.
- Common mistake: using the wrong size collet for the tungsten diameter (it may “kind of” hold, but alignment and conductivity suffer).
Collet body
The collet body is the threaded part that screws into the torch body. It provides the seat for the collet and forms the gas path to the cup. It also determines whether you are using a standard setup or a gas lens setup.
- Key job: mechanical alignment + gas routing.
- Common mistake: cross-threading or under-tightening, causing gas leaks and inconsistent shielding.
Back cap (long/medium/short)
The back cap seals the rear of the torch and provides the clamping force that locks the tungsten in place. Different lengths affect access: a short cap helps in tight spaces, while a long cap provides more internal room for longer tungsten stick-out and can be easier to tighten consistently.
- Listen to the audio with the screen off.
- Earn a certificate upon completion.
- Over 5000 courses for you to explore!
Download the app
- Key job: seal and clamp.
- Common mistake: over-tightening (can deform collet) or leaving it slightly loose (tungsten can shift mid-weld).
Ceramic cup (nozzle)
The ceramic cup shapes and directs the shielding gas around the tungsten and weld puddle. Cup size (often referenced by “#” size) affects how wide the gas coverage is and how much tungsten stick-out you can use without losing shielding. A chipped or cracked cup can disrupt gas flow and create turbulence, which pulls in air.
- Key job: create a stable gas envelope.
- Common mistake: using too small a cup for the joint access or tungsten stick-out needed.
Standard Collet Body vs Gas Lens: How They Affect Coverage and Arc Stability
Standard setup (standard collet body)
A standard collet body delivers gas through relatively direct passages. It works well for many routine joints, but gas flow can be more turbulent—especially when you increase stick-out or weld in drafty positions. Turbulence reduces effective shielding and can cause discoloration or soot.
- Strengths: simple, common, durable.
- Limitations: less forgiving with long stick-out; can be more sensitive to gas flow settings and torch angle.
Gas lens setup
A gas lens uses a diffuser screen (sintered mesh) to straighten and smooth the gas flow. This produces a more laminar gas column, improving coverage and making the arc feel steadier. A gas lens is especially helpful when you need extra tungsten stick-out for access (inside corners, fillets, tight joints) while still maintaining shielding.
- Strengths: better shielding coverage, more stable arc feel, supports longer stick-out.
- Limitations: diffuser can be damaged by spatter/impact; must be kept clean and not crushed.
| Feature | Standard setup | Gas lens |
|---|---|---|
| Gas flow character | More turbulent | More laminar/straightened |
| Shielding tolerance with long stick-out | Lower | Higher |
| Arc “wandering” resistance | Moderate | Better (often steadier) |
| Best use | General access, shorter stick-out | Tight access, longer stick-out, cosmetic/clean work |
Correct Assembly Order and Fit (Step-by-Step)
Consumables must match each other: the tungsten diameter must match the collet size, and the cup must match the collet body type (standard vs gas lens) and thread style.
Step-by-step torch assembly
Select matched parts. Choose the correct collet for your tungsten diameter, and choose either a standard collet body or a gas lens body that fits your torch. Confirm the cup matches the chosen body type.
Install the collet body (or gas lens body) into the torch. Thread it in by hand first to avoid cross-threading, then snug it. It should seat firmly; if it bottoms out crooked or feels gritty, stop and inspect threads and sealing surfaces.
Slide the collet into the collet body. The collet should seat smoothly. If it feels loose or binds, verify it’s the correct size and not deformed.
Insert the tungsten from the front (cup side). Push it through the collet until it reaches the desired stick-out. Inserting from the front helps prevent dragging the tungsten through debris that may be inside the back cap area.
Thread the back cap on and tighten to clamp. Tighten until the tungsten is held securely and cannot rotate or slide with light finger pressure. Avoid excessive force; you want secure clamping without crushing the collet.
Install the ceramic cup. Thread it on gently and snug it. Do not over-tighten; ceramic can crack and threads can be damaged.
Final checks. Ensure the tungsten is centered in the cup opening, the cup is not chipped, and all parts are snug. A quick visual alignment check prevents many arc stability issues.
Tungsten Stick-Out: How Far and Why It Changes
Stick-out is the distance the tungsten extends past the cup. More stick-out improves access and visibility, but it reduces shielding effectiveness because the tungsten tip is farther from the cup’s gas envelope. The goal is the minimum stick-out that still gives you access.
Practical stick-out guidelines
- General work (good access): short stick-out for strongest shielding and easiest starts.
- Inside corners/fillets/tight joints: moderate stick-out to reach the joint while keeping the cup close enough to shield.
- Extended reach needs: longer stick-out is more successful with a gas lens and a larger cup to maintain coverage.
Rule-of-thumb pairing: cup size, stick-out, and access
| Situation | Preferred setup | Stick-out approach | Why |
|---|---|---|---|
| Flat butt joint with room | Standard or gas lens | Short | Max shielding, stable arc, clean color |
| Fillet weld with moderate access | Gas lens helpful | Moderate | Better coverage as torch angle changes |
| Tight corner / restricted cup clearance | Gas lens + appropriate cup | Moderate-to-long (only as needed) | Maintains gas coverage with extended reach |
| Long stick-out attempt with small cup | Avoid if possible | Often problematic | Shielding breaks down; contamination likely |
Fit check: if the tungsten is not centered in the cup opening, re-check collet size, collet condition, and whether the collet body is seated squarely.
How Each Component Affects Gas Coverage and Arc Stability
- Cup condition and size: larger cups generally provide a wider gas envelope; damaged cups create turbulence and weak spots in shielding.
- Gas lens vs standard: gas lens smooths flow, improving shielding consistency and reducing sensitivity to small torch angle changes.
- Collet grip and alignment: off-center tungsten can make the arc “pull” to one side and can cause uneven heating of the cup and tungsten.
- Back cap tightness: loose caps allow micro-movement of tungsten, causing erratic arc length and unstable starts.
- Thread fit and sealing surfaces: poor seating or damaged threads can leak gas before it reaches the cup, reducing coverage at the weld.
Troubleshooting: Symptoms → Likely Torch Setup Causes → Fix
Wandering arc (arc won’t stay where you aim)
- Likely causes (torch setup):
- Tungsten not centered due to wrong collet size or worn collet.
- Collet body not seated squarely (cross-threaded or debris on seat).
- Loose back cap allowing tungsten to shift.
- Damaged gas lens diffuser causing uneven gas flow (less common, but can contribute).
- Fix:
- Verify collet matches tungsten diameter; replace collet if it clamps unevenly.
- Remove collet body, inspect threads and seating surfaces, reinstall hand-tight then snug.
- Tighten back cap until tungsten cannot twist or slide.
- If using a gas lens, inspect diffuser for dents/contamination; replace if damaged.
Poor shielding (dull/oxidized bead, inconsistent color, “hazy” puddle)
- Likely causes (torch setup):
- Cup too small for the stick-out being used.
- Stick-out too long for the setup (especially standard collet body).
- Cracked/chipped cup creating turbulence.
- Loose cup or loose collet body leaking gas at threads.
- Wrong cup type for the body (mismatch between gas lens cup and standard body, or vice versa).
- Fix:
- Reduce stick-out and keep the cup closer to the work.
- Switch to a gas lens if you need longer stick-out for access.
- Replace damaged cup; do not “make it work” with chipped ceramic.
- Snug the cup and collet body; reassemble to ensure proper seating.
- Confirm consumables are compatible (correct series/type for your torch and chosen body).
Black soot around the weld (or heavy gray/black deposits)
- Likely causes (torch setup):
- Shielding gas coverage breaking down due to excessive stick-out or too small a cup.
- Cracked cup or loose consumables causing turbulent flow and air entrainment.
- Gas lens diffuser damaged or clogged, disrupting laminar flow.
- Fix:
- Shorten stick-out and/or move to a larger cup.
- Reassemble and snug all threaded parts; replace any cup with chips/cracks.
- Inspect gas lens screen; replace if contaminated or physically damaged.
Erratic starts (hard to initiate arc, inconsistent ignition, arc “spits”)
- Likely causes (torch setup):
- Loose back cap or collet causing poor electrical contact to tungsten.
- Wrong collet size (intermittent clamping/contact).
- Tungsten slipping during start because it isn’t clamped firmly.
- Consumables overheated/damaged leading to poor fit (collet deformed, body threads rough).
- Fix:
- Disassemble and reassemble: correct collet size, clean seating surfaces, snug collet body.
- Tighten back cap to secure tungsten; verify it cannot move.
- Replace worn collets or damaged collet bodies that no longer seat smoothly.
Porosity appearing “randomly” after a few good inches
- Likely causes (torch setup):
- Cup loosening as the torch heats up.
- Back cap loosening, allowing tungsten movement and changing stick-out mid-weld.
- Hairline crack in cup opening up with heat.
- Fix:
- After the torch cools, check tightness of cup and back cap; reassemble and snug.
- Replace suspect cups; inspect carefully under good light for fine cracks.
- Confirm the tungsten remains centered and at the intended stick-out.
Quick Reference: Assembly and Setup Checks
- Match sizes: tungsten diameter = collet size.
- Match types: cup must match standard vs gas lens body.
- Centering: tungsten should appear centered in cup opening.
- Snug, not forced: collet body and cup seated firmly; ceramic not over-tightened.
- Stick-out: use the shortest stick-out that still gives access; increase cup size and consider a gas lens when you must extend.
