Electric Arc Welding Diagram: A Complete How-To Guide

A fabricator once set a bracket into a fixture, glanced at the print, and welded a solid fillet all around a joint nobody wanted. The drawing was not wrong; it simply carried a symbol he had never decoded. An electric arc welding diagram is the shorthand that turns a stack of blueprints into a repeatable, inspectable, code-compliant weld, and once you can read it, shop conversations change completely.

What Is an Electric Arc Welding Diagram? Three Diagrams, One Search Term

An electric arc welding diagram is any drawing that communicates how arc welding will be done: where the arc goes, what process makes it, how big the weld is, and how power reaches the arc.

Here is the catch. Shop floors, textbooks, and search bars use that phrase for three different documents: a weld symbol on a fabrication print, a joint detail showing a butt versus a tee, and a schematic tracing power from machine to workpiece. Each answers a different question, and this guide covers all three.

1. Weld Symbol Drawings and Shop Blueprints

This is the document most people picture: an engineering or fabrication print carrying weld symbols on the reference line. It gives joint type, weld size, length, process, and position. It is the instruction the shop is paid to follow, and what an inspector reads to judge the weld.

2. Joint and Assembly Diagrams

These show the geometry before any symbol is applied: butt, lap, tee, corner, and edge joints, plus exploded or assembled views showing where each weld lands. They answer “what goes where,” not “how big is the weld.” In a drawing package, the assembly view says which joints get welded, the detail sheet says how.

3. Machine and Circuit Schematics

The least visible category, and the one that causes the most confusion. A power-flow schematic traces the path electricity takes: primary supply, transformer, rectifier, inverter, output terminals, electrode lead and holder, the arc, the workpiece, and the return through the work clamp. It is a maintenance document, not a fabrication instruction.

A Shop Scenario Where the Distinction Matters

Picture a stainless pipe spool. The package holds a spool drawing with fillet symbols on the nozzle, a joint detail sheet showing beveled butt preparation, and a photocopied power manual page with DC and DCEN wiring.

An apprentice handed the manual page asks the lead for amperage and filler metal. The lead says “look at the drawing” and hands over the spool sheet, which calls for GTAW with a symbol and size but no amps. He has also clamped the work lead to the pipe hanger instead of the workpiece, and the power-flow schematic shows where the return path belongs.

Three drawings, three answers: the joint detail says how to prepare the metal, the symbol sheet says what weld to make, and the schematic says how to connect the machine so the arc behaves. Why SMAW still wins in many shops shows how a process choice only makes sense once you know which document is driving the job.

Who Actually Reads These Drawings

• Welders need symbols and joint details to set up joint, position, and consumable.
• Fabricators and fitters need assembly views for fit-up, sequence, and how the weld fits the part.
• Inspectors and QA need symbols for acceptance criteria, then check the finished weld.
• Engineers create and revise the drawings, owning strength, fatigue life, and distortion decisions.
• Students and new hires use them as a first test of reading a print, alongside resources like TWI or AWS training programs.

Who Owns Which Document

In a disciplined shop, three separate records govern a weld, and confusing them causes trouble:

Document	What it controls	Role
Welding drawing	Joint type, weld symbol, size, length, position, notes	The contract. What must exist when the job is done.
WPS and PQR	Parameters, consumables, preheat, sequence, qualification range	The procedure. The repeatable, tested method that produces that weld.
Inspection report	Visual results, NDT reports, measurements, welder IDs	The evidence. Proof the contract was met.

The Welding Procedure Specification describes the steps, and the Procedure Qualification Record proves a welder and procedure combination passed a test showing it works. AWS standards such as D1.1 for structural steel, and ASME BPVC Section IX for welder and procedure qualification, turn a drawing symbol into a qualified weld rather than an opinion. OSHA’s welding requirements, including 29 CFR 1910.252, cover how the work must be performed and protected.

A misread fillet size means an oversized leg a customer’s fit check rejects. A symbol on the wrong side means a weld nobody ordered, in a spot that might weaken fatigue performance. A leg-versus-throat mix-up means the weld looks right but is undersized by nearly 30 percent, then fails the ultrasonic test. Every one of those ends the same way: rework, scrapped material, a failed inspection, a schedule slip.

Anatomy of a Weld Symbol: Arrow Side, Other Side, and the Reference Line

Hand five welders the same weld symbol and you can get five different welds out of it. Not because they cannot run a bead, but because the symbol is a coded instruction and each decoded it differently. Learn that code and every symbol you meet afterward hangs on the same short grammar.

A weld symbol is not a picture of a weld. It is a sentence with a fixed structure: an arrow, a reference line, and a set of slots where each piece of information has exactly one legal place to sit. Every electric arc welding diagram, from a single fillet callout to a full structural detail, uses that same grammar.

The three parts of every symbol

• The arrow. A leader line ending in an arrowhead. The critical point: the arrow points to the joint, the line where two members meet. It does not point to the weld, and it is not supposed to. The arrow also defines the two sides of the joint. The arrow side is the side of the joint the arrow points at, the member you are being directed to weld. The other side is the member on the opposite face of that joint.
• The reference line. The horizontal (or vertical) line that carries the symbol. Every instruction hangs off it.
• The tail. The short elbow at the far end of the reference line, where a shop adds information the symbol cannot carry: a WPS number, a process note, or a reference to a general note. Many drawings simply omit it.

Where each piece of information goes

Element	Position on the reference line	What it tells you
Basic symbol (fillet triangle, square, V, U, J)	Center	Weld type
Groove or fillet size	Left of the basic symbol	Weld dimension
Weld length	Right of the basic symbol	Length of weld
Contour and supplementary flags (flush, convex, concave, melt-through, backing)	Opposite side of the reference line from the weld	Surface and detail requirements
Process letter and position code	Below the basic symbol	How to run it, for example S for SMAW with 3G or 1F
All-around circle	At the junction of the arrow and the reference line	Weld continues around the entire joint
Field weld flag	Arrow side of the reference line	Weld is made on site, not in the shop

The all-around symbol is a circle drawn where the arrow meets the reference line. It means the weld runs continuously around the full perimeter of the joint, whether the shape is a tube, a box section, or a ring. The field weld symbol is a small flag placed on the arrow side of the reference line, and it is the detail examiners love to ask about.

Underneath the basic symbol you will find a process letter. S means shielded metal arc, the stick process many shops still favour for structural work and outdoor fabrication, as explained in why SMAW still wins. Alongside it sits a position code such as 1F or 3G, telling the shop which welding position the procedure is qualified for. The full lettering scheme is set out in the AWS welding standards.

Reading one symbol out loud

Picture a bracket drawing. The arrow touches the fillet joint where the bracket meets the base plate, and the reference line runs off to the right. Reading it aloud:

“Arrow to the joint, so we are looking at the bracket side. Fillet triangle in the center, so it is a fillet weld. Size 6 mm to the left of the triangle, so a 6 mm fillet. Length 100 mm to the right, so 100 mm long, not continuous. Below the triangle, MA and 1F, so gas metal arc welding in the flat position. On the opposite side of the line, a flush contour symbol, so the bead gets dressed level. No circle at the junction, so not an all-around weld, and no flag, so it gets welded in the shop.”

Say that back to a lead and the ambiguity is gone. The TWI resources on weld symbols are worth keeping open in another tab while you practise, because the syntax only sticks once you speak it.

The mistake that costs the most

Beginners routinely flip the reference line to the wrong side of the joint, or put the symbol above the line instead of below it. Side placement is not cosmetic: it decides which member receives the weld. If the reference line leaves the joint on the arrow side, the symbol beneath it describes a weld on the arrow-side member. If it leaves on the opposite side, the same symbol describes a weld on the other-side member. Flip it and you have silently reordered the job, which is how a bracket ends up with a full fillet where the drawing wanted only a stitch at one end. Place the arrow on the joint, keep the symbol on the correct side, and clarify any ambiguous drawing before the steel is cut.

Groove and Fillet Symbols: The Five Joint Types You’ll Actually Weld

Every arc welding diagram comes back to one question: what shape are the metal pieces in, and how do you join them? Name the joint and the weld symbol nearly picks itself, and fabricators who know the five basic joints read drawings faster.

The Five Basic Joint Types

A butt joint puts two members edge to edge in the same plane, so you weld right through the material for the strongest welds. Lap joints overlap one member over another, creating an L-shaped fillet along the edge. Tee joints set one member perpendicular into the face of another. Corner joints work like tee but with members meeting at an angle, forming an L. Edge joints butt two flanges or edges together for thin sheet where groove welds are impractical.

Joint	Typical weld symbol	Where you meet it
Butt	Square, V, bevel, U or J groove	Pressure vessels, pipe, structural plate
Lap	Fillet (triangle)	Shear connections, decking, built-up plate
Tee	Fillet or groove	Frame members, tube-to-plate work
Corner	Fillet	Box fabrication, guard rails
Edge	Flare V-groove or square groove	Thin sheet, flanges, ductwork

Groove Welds: Five Shapes, Five Jobs

Groove welds are named for the channel prepared between the pieces. The symbol shows its cross-section.

• Square groove: Two parallel faces butted together with no edge preparation. Cheap and ideal for thin material, but it needs accurate fit-up: a square groove cannot fill a gap.
• V-groove: A single bevel on one or both edges forming a V. Dominant in structural carbon steel, it deposits more metal than a square groove yet stays easy to weld.
• Bevel groove: A single bevel on one edge only. Used on thicker plate or one-sided welds where access is limited, usually seen inside a double-V detail.
• U-groove: A rounded channel. The wide root opening reaches the joint bottom with less heat input than a narrow V and gives a smoother profile, but preparation is costly.
• J-groove: A deep narrow groove with a curved back and straight face. Heat input stays low, which suits thick sections, tooling, and repairs where you want to limit distortion and burn-through.

Fillet Welds: The Triangle Everyone Recognises

The fillet symbol is the right triangle, covering most metal fabrication. A single triangle means one fillet; a mirrored pair means a double fillet for joints needing metal on both sides, or where one side seals and the other carries load.

Where the numbers go is where disputes start. Under AWS A2.4, the metric-era convention, a fillet size is the leg length: one side of the triangle measured along the joint. The older inch-based practice specified the throat, the shortest distance from root to face, equal to the leg multiplied by 0.707. A 10 mm fillet has roughly a 7 mm throat, and mixing the two conventions leaves you with a thinner weld than the drawing demands.

Most fillets are equal-leg, so one triangle with one leg dimension works. When the legs differ, use the unequal-leg symbol, a right triangle with the vertical leg longer, dimensioned on the longer leg.

Two more symbols sit opposite the reference line: the backing symbol (B), marking a permanent or temporary backing bar that supports molten metal, and the contour symbols for flush and flat, convex, and concave faces.

Why Joint Design Changes the Whole Job

Joint design is not a drafting preference. It dictates the process, fit

Groove and Fillet Symbols: The Five Joint Types You’ll Actually Weld

Every arc welding diagram comes back to one question: what shape are the metal pieces in, and how do you join them? Name the joint and the weld symbol nearly picks itself.

The Five Basic Joint Types

A butt joint puts two members edge to edge in the same plane, so you weld right through the material for the strongest welds. Lap joints overlap one member over another, creating an L-shaped fillet along the edge. Tee joints set one member perpendicular into the face of another. Corner joints work like tee but with members meeting at an angle, forming an L. Edge joints butt two flanges or edges together for thin sheet where groove welds are impractical.

Joint	Typical weld symbol	Where you meet it
Butt	Square, V, bevel, U or J groove	Pressure vessels, pipe, structural plate
Lap	Fillet (triangle)	Shear connections, decking, built-up plate
Tee	Fillet or groove	Frame members, tube-to-plate work
Corner	Fillet	Box fabrication, guard rails
Edge	Flare V-groove or square groove	Thin sheet, flanges, ductwork

Groove Welds: Five Shapes, Five Jobs

Groove welds are named for the channel prepared between the pieces. The symbol shows its cross-section.

• Square groove: Two parallel faces butted together with no edge preparation. Ideal for thin material, but it needs accurate fit-up: a square groove cannot fill a gap.
• V-groove: A single bevel on one or both edges forming a V. Dominant in structural carbon steel, it deposits more metal than a square groove yet stays easy to weld.
• Bevel groove: A single bevel on one edge only. Used on thicker plate or one-sided welds where access is limited, usually seen inside a double-V detail.
• U-groove: A rounded channel. The wide root opening reaches the joint bottom with less heat than a narrow V and gives a smoother profile, but preparation is costly.
• J-groove: A deep narrow groove with a curved back and straight face. Heat input stays low, suiting thick sections, tooling, and repairs where you want to limit distortion.

Fillet Welds: The Triangle Everyone Recognises

The fillet symbol is the right triangle, covering most metal fabrication. A single triangle means one fillet; a mirrored pair means a double fillet for joints needing metal on both sides, or where one side seals and the other carries load.

Where the numbers go is where disputes start. Under AWS A2.4, the metric-era convention, a fillet size is the leg length: one side of the triangle measured along the joint. The older inch-based practice specified the throat, the shortest distance from root to face, equal to the leg multiplied by 0.707. A 10 mm fillet has roughly a 7 mm throat, and mixing conventions leaves a thinner weld than the drawing demands.

Most fillets are equal-leg, so one triangle with one leg dimension works. When the legs differ, use the unequal-leg symbol, a right triangle with the vertical leg longer, dimensioned on the longer leg.

Two more symbols sit opposite the reference line: the backing symbol (B), marking a permanent or temporary backing bar that supports molten metal, and the contour symbols for flush and flat, convex, and concave faces.

Why Joint Design Changes the Whole Job

Joint design is not a drafting preference. It dictates the process, fit-up tolerance, number of passes, whether the joint can be machined afterwards, and how an inspector verifies it.

A square groove in 6 mm plate gets one short GMAW pass in minutes. The same thickness with a U-groove would be machined, tacked carefully, then welded multi-pass in a confined position. A clean single-pass fillet is usually inspected visually, while a double fillet on a load-bearing bracket might trigger magnetic particle or ultrasonic testing, depending on the code.

Material matters too. Aluminium behaves differently from steel, since you are dealing with conductivity and cracking risk rather than section thickness. Our guides on aluminum MIG welding and aluminum flux core welding cover those differences.

The takeaway: identify the joint, then the symbol, then confirm the process fits. If a drawing calls for a 10 mm V-groove in 30 mm plate and your shop has only a 6 mm V prep, that is a document problem, not a welding problem. Settle it against the WPS before striking the arc.

Process, Position, and Size: What the Extra Symbols on a Diagram Mean

A bare weld symbol gives you the shape of the joint, not how it gets made. The modifiers around it name the process, the position, the bead size and the finished surface. Read them correctly and the drawing becomes an instruction sheet everyone reads the same way.

The Process Letter: Which Machine Does the Work

The letter below the basic symbol names the joining process. In AWS drawings these are codes, not trade names, which trips up newcomers:

• S – shielded metal arc welding (SMAW), the stick process. Why it still wins on many jobsites is covered in why SMAW still wins.
• M or MA – gas metal arc welding (GMAW), what most people call MIG.
• F or FA – flux cored arc welding (FCAW).
• W or GT – gas tungsten arc welding (GTAW), or TIG.
• SA – submerged arc welding.

“MA” is the AWS code for what AWS calls GMAW in D1.1, and “GT” is AWS for GTAW. If your WPS says GMAW and the print says MA, that is the same process, not a conflict. ISO 2553 uses numbers instead: 111 for SMAW, 131 for GMAW, 135 and 136 for FCAW, 141 for GTAW, 121 for submerged arc. The shapes line up across regions, so a symbol learned in one country reads correctly in another. The TWI welding symbol guide is a good cross-check, and A2.4 sits in the AWS standards library.

Position Codes: 1 Through 4, Plus a Letter

Position codes tell you where the welder and the part will be during the weld. The number is the position, the letter is the type of joint:

• 1 flat, 2 horizontal, 3 vertical, 4 overhead
• G groove weld, F fillet weld

Read “3G” as vertical groove and “1F” as flat fillet. AWS A2.4 places the designation beside the basic symbol, while ISO 2553 appends it after the process number, so the same weld appears as 135 PA on a European drawing. With no position code shown, flat is normally assumed unless the general notes say otherwise.

A 3G or 4G on a print is usually a qualification requirement, not a technique suggestion. Codes tie welder qualification to the positions passed, so a shop taking 3G and 4G work needs welders whose certification records cover those positions. That is also why position belongs in the all-position electrode guide: a rod that runs beautifully flat and vertical can still be the wrong pick overhead.

What a 3G or 4G Changes at the Machine

Position codes drive real decisions:

• 3G vertical up – uphill travel, stringer beads, short arc, steady puddle control, and a pause at the root so slag runs off the top.
• Vertical down – travel with the puddle, faster and flatter penetration, more spatter. Common with self-shielded flux core on thinner material, and avoided on stainless, where extra heat discolours the bead.
• 4G overhead – stringers, minimal dwell, a work angle of roughly 60 to 80 degrees, and the fastest travel speed that still gives full fusion.
• 1F and 1G – where technique gets built. The aerospace TIG guide covers how much position shifts GTAW, where amperage is set by hand rather than by the machine.

Size, Length and Spacing

The size sits left of the basic symbol for the arrow side, or on the opposite side for the other side of the joint. Under AWS A2.4 a fillet size is the leg length, measured across the outside of the joint. A small throat symbol at the junction of the arrow and reference line changes the meaning to effective throat, the shortest distance from root to face. The leg measures both members; the throat measures only the fused metal. Confuse the two and you under-specify the joint.

The length sits to the right of the basic symbol in millimetres, and intermittent welds add a pitch or centre-to-centre spacing value. A field weld flag means the joint is welded on site, where the drawing cannot control fit-up.

Supplementary Symbols

• Flush or flat – a straight line across the symbol: machined or ground flush.
• Convex – a shallow bulge: the weld stands proud of the surface.
• Concave – a hollowed curve: the weld is dished in.
• Melt-through – applied to the back side, calling for visible root reinforcement that is cut off later.
• Backing – a permanent bar or strip under the joint.

On the drawing	What it instructs	Machine setup
Fillet triangle + “6” + MA	6 mm leg fillet, GMAW	75/25 mix, 0.035 solid wire, 110–130 A, 20–22 V
V-groove + “5” + MA	Single pass, 5 mm root groove	Short-circuit transfer, 0.030 wire, 95–115 A, 18–20 V
Square groove + MA	Square-groove butt, fill and cap	Spray transfer, 0.045 wire, 26–30 V, WFS around 280 ipm
Fillet + S	Fillet by stick	E7018 3/32, 90–130 A DCEN, electrode angle into the toe
Fillet + GT	Fillet by TIG, no filler	DCEN, tungsten sized to amps, 10–12 V, HF start
V-groove + 3G	Vertical up groove weld	Stringer beads, uphill travel, reduced wire feed speed

How to Draw Your Own Electric Arc Welding Diagram (Step by Step)

Drawing an electric arc welding diagram is less artistic than most people expect. The drawings that trip up a fabricator are rarely the ugly ones. They are the vague ones: a symbol on the wrong side, a fillet size with no units, a sheet that never says which code governs it. Follow a repeatable sequence and you can produce a shop-ready weld drawing with a pencil, a template, and a steady afternoon. Break the sequence and no amount of polished CAD saves the job.

The step-by-step workflow

1. Define the assembly first. Start with the parts, not the symbol. What joins what, what material, what thickness, and how much of the joint gets welded? A quick joint sketch on the same sheet prevents an argument later.
2. Choose the joint, then the matching symbol. Butt joints take groove symbols (square, V, bevel, U, J). Lap and tee joints take the fillet triangle. Corner and edge joints take either, depending on access.
3. Add size and length. Fillets get a size plus, often, a length and pitch. Grooves get depth and effective throat. “Weld 50 mm long” is half an instruction. “50 mm long, 75 mm pitch” tells the welder where to stop and restart.
4. Add the process letter and position code. The letter below the basic symbol (S for SMAW, M for GMAW, F for FCAW, W for GTAW) plus a code such as 1F or 3G locks the procedure down. Leave the position blank and the procedure decides, not the drawing.
5. Place the symbol on the correct side of the reference line. Arrow side versus other side. A symbol below the reference line means the weld is required on the arrow side, and reversing it reverses the meaning.
6. Add flags and notes. The all-around circle, the field weld flag, contour symbols, and notes such as “weld all around” or “seal weld”.
7. Cross-check against the WPS and the code. Confirm the symbol, base material and process all agree with the qualified procedure. The ASME BPVC standards and the AWS standards catalogue at aws.org/standards set expectations for pressure and structural work. If the symbol and the WPS disagree, resolve it before anyone lights an arc.
8. Close with title block, units and a revision block. Always state the governing code and the drawing revision on the sheet.

Choosing your drafting tools

Method	What it takes	Best for
Hand drafting	Pencil, straightedge or triangle, plus weld symbol templates or stencils	One-off shop drawings, repair work, sketching a joint before quoting
CAD blocks	AutoCAD block libraries with saved weld symbol definitions	Repeat work on assemblies sharing the same welds
CAD weldment tools	SolidWorks or Fusion 360 weldment symbols tied to the model	Sheet metal work where welds follow part geometry
Free vector editors	Inkscape or diagrams.net	Fast markups, field fixes, sharing a corrected detail

Build a symbol library once

The single biggest time saver is a library of your own blocks. Save each symbol once with its reference line, arrow, tail and flags already correct, then insert it as a block instead of redrawing it. That kills symbol-placement errors, because a saved block always lands with the arrow and the line in the right relationship. Keep a companion file pairing each block with the process letter and position code you use most often.

The drafting mistakes that cause real problems

• Missing units. A fillet size of 6 with no unit means 6 mm or 6 inches. State units on the sheet, ideally both.
• Ambiguous fillet size convention. Say whether the value is leg or throat, and say so in a general note.
• Symbol on the wrong side. Arrow side versus other side reversed means the weld goes where it should not.
• No process letter. Without it, the shop picks, and the shop may pick wrong.
• Unlabelled all-around. A circle placed by habit instead of intention causes work where none is wanted.
• Unreadable line weights. If the symbol vanishes into the outline, it is not a document.

Checklist you can copy onto the sheet

• Assembly, material and thickness identified
• Joint type selected and correct basic symbol drawn
• Size, length and pitch noted
• Process letter and position code added
• Symbol placed on the correct side of the reference line
• All-around or field weld flagged deliberately
• Units and fillet size convention stated in a general note
• Cross-checked against the WPS and the governing code
• Title block, governing code and revision block complete

Machine Diagrams: How an Arc Welding Circuit Actually Works

A weld symbol says what to build. A machine diagram shows how the current gets there. Trace the loop from panel to puddle and the welder stops being a black box. Here it is, in order from supply to puddle and back:

1. Primary supply. 240 V single-phase or 480 V three-phase; check the nameplate for what your welder expects.
2. Step-down transformer. Lowers primary to a secondary voltage that drives the arc.
3. Rectifier. A diode bridge converts the AC secondary into DC.
4. Inverter or SCR chopper. Switches DC at high frequency, or chops it with silicon-controlled rectifiers, to shape current rise, fall and pulse behaviour.
5. Output terminals. Electrode lead and work lead.
6. Electrode holder or gun. Holds the consumable and contacts the arc.
7. The arc. Ionized gap where current changes form and heat is generated.
8. The workpiece. The metal joined, completing the electrical path.
9. Ground clamp. Bolted to the workpiece, carrying current back.
10. Return path. Current re-enters the machine, closing the loop.

That last point is where beginners get lost: electricity needs a complete loop, and nothing is pushed from the machine. A clamp on scale, paint or rust chokes the circuit, so the welder raises voltage to compensate and a clean, bare clamp point matters.

Transformer, Rectifier, Inverter

The block diagram is universal, but the middle has changed over the decades.

Power source	Output	Typical processes	Character
Transformer	AC	SMAW, AC TIG, some FCAW	Simple, heavy, hums under load; limited current-shape control.
Rectifier	DC	SMAW, GMAW, FCAW	A diode bridge on a transformer; standard DC for decades.
Inverter	DC with AC for TIG	Every major process, plus pulsed TIG and cutting	Fast current response, compact, multi-process, with pulse modes.

Most shops run inverters because one box switches between stick, MIG and TIG and pulse gives control transformers cannot. Older AC and DC machines remain common in heavy fabrication and agricultural shops, and the reasons stick welding still wins in many bays come down to this forgiving circuitry as much as to the process itself.

Constant Current Versus Constant Voltage

Constant current (CC) machines hold amperage nearly steady even when arc voltage shifts. Voltage is not the control variable, so the welder sets arc length and voltage rises and falls to match. Stick and TIG run on constant current, which is why TIG welders switch current with a foot pedal or torch trigger, not a voltage knob. For finer heat control, aerospace TIG welding pushes pulse logic to its limits.

Constant voltage (CV) machines hold voltage steady and let current change to suit the load. MIG and flux-cored wire welding run on CV: the wire feeder pushes consumable at a set speed and arc voltage controls how fast the wire melts. Set wire feed speed and matching voltage and the machine manages current for you. Think amps on a CC machine, voltage plus wire feed on a CV machine.

Polarity: Which Way the Current Flows

• DCEP (electrode positive, reverse polarity). Standard for most SMAW and for steel GMAW with solid wire. Deeper penetration, shorter stiffer arc, wider bead, more spatter.
• DCEN (electrode negative, straight polarity). Default for GTAW on steel, stainless and aluminium, and for solid-wire GMAW on aluminium. Less penetration, wider flatter bead, less spatter, better on thin material.
• AC. Required for TIG on aluminium, since aluminium oxide insulates and only the electrode-positive half of the cycle burns it off. Some SMAW electrodes also run on AC.

Aluminium is where polarity mistakes get expensive. A machine left on DCEP for an aluminium MIG job can throw spatter and undercut a tube. Our aluminium MIG welding guide covers gun setup, pulse settings and polarity changes that keep such jobs clean.

Circuit Safety Rules From OSHA 1910.254

The federal standard is specific about the return path, where shop accidents happen. Under 29 CFR 1910.254:

• Every welding power source frame or case must be grounded to protect operators against shock from a faulty machine.
• Conduits containing conductors must not be used to complete a work-lead circuit.
• Pipeline or piping must not be a permanent part of the work-lead circuit, and current must not pass through threaded, flanged or caulked joints.
• Chains, wire ropes, cranes, hoists and elevators must never carry welding current.
• Ground connections must be mechanically strong and electrically adequate.
• Open-circuit voltage is capped: 80 V for manual AC arc welding, 100 V for automatic AC, and 100 V for manual and automatic DC welding.

Cables and Holders

OSHA’s rules on holders, cables and connectors, in 29 CFR 1910.253, are just as specific: cables with splices within 10 feet of the holder must not be used, because a splice that close to the grip is a heat and shock hazard; any cable with damaged insulation or exposed conductors must be replaced, not taped up; and holders must be stored so they cannot contact people, metal, fuel or gas cylinders.

Switch the machine off before touching a lead and most arc welding electrical problems never happen. Trace the circuit once on paper and the diagram stops being theory.

I’ll rewrite this section, keeping the heading, facts, and all links while tightening it into the target range.

Safety Diagrams: PPE, Ventilation, and Fire Watch Rules You Can Put on Paper

Weld symbols tell you where the metal goes, not who gets hurt. A 5 mm fillet weld in 3G means nothing to a welder in a closet with no hood and a shade 8 helmet. A serious electric arc welding diagram needs a safety companion: a separate sheet or hot work permit, built on OSHA 1910.252 and 1910.253 for welding, cutting, and brazing.

Eye and Face Protection: The Filter Shade Table

Arc light carries infrared and ultraviolet radiation that burns your retina and cornea in a fraction of a second. Shade number must match process and electrode diameter. OSHA Table D-3 gives the starting points:

Process	Minimum Filter Shade
SMAW, 1/16–5/32 in	Shade 10
SMAW, 3/16–1/4 in	Shade 12
Gas-shielded arc, ferrous	Shade 12
Gas-shielded arc, nonferrous	Shade 11
SMAW, 5/16–3/8 in	Shade 14
Carbon arc	Shade 14

Nonferrous gas-shielded work takes a lighter shade (11) than ferrous (12) because the arc is less intense, and on aluminum the arc is nearly invisible.

1910.133 requires a face shield with a filter lens, plus safety glasses or goggles underneath for grinding and chipping. Gauntlet gloves, a flame-resistant jacket, and leather footwear cover the rest.

Fire Prevention and the Fire Watch

Move combustibles at least 35 feet (10.7 m) from the work when practicable. If that is impractical, guard them with noncombustible or fire-resistant covers and keep the fire watch in place.

A fire watch is required when the work involves flammables, when combustibles cannot be moved 35 feet, or in a confined space with hazardous atmosphere potential.

• During the work: on site, access to extinguishers, watching for fire in and around the area, including spots the welder cannot see.
• After the work: maintained at least half an hour after welding or cutting ends, to catch smouldering material that has not surfaced.

Thirty minutes catches smouldering rags, sandwich panel insulation, and concealed deck fires that develop slowly. If work moves mid-shift, the watch moves with it. NFPA 51B covers cylinder and fuel gas staging.

Ventilation: When Mechanical Ventilation Is Mandatory

Under 1910.252(c)(2), general ventilation must hold fume below the 1910.1000 limits, and 1910.1000 requires engineering and administrative controls first, with respirators only where those controls fall short.

Mechanical ventilation is required when:

• the welding space is under 10,000 cubic feet per welder
• the ceiling is under 16 feet
• the work is in a confined space
• cross-ventilation is obstructed

The minimum rate is 2,000 cubic feet per minute per welder, a floor for general ventilation, not a substitute for local exhaust. Hoods do the real work, and OSHA rates airflow by hood distance:

Hood-to-Arc Distance	Minimum Airflow
4–6 in	150 cfm
6–8 in	275 cfm
8–10 in	425 cfm
10–12 in	600 cfm

The design target is 100 linear feet per minute, and the closer the hood sits to the arc, the less airflow it needs. TWI has extraction design guidance.

Respiratory Protection and Confined Space Work

Welding stainless or lead-coated surfaces indoors, or in a confined space, requires local exhaust ventilation or airline respirators. They must be NIOSH-approved under 42 CFR Part 84 and used under a written respiratory protection program with fit testing and medical clearance. An air-purifying respirator will not protect you against lead or cadmium fumes.

Beryllium is stricter. It is a carcinogen OSHA moved into 1910.1200 for exposure limits and regulated areas, so welding beryllium means enclosure, dedicated local exhaust, and a regulated-area perimeter.

Manganese and the Limits That Matter

Know your numbers:

Authority	Limit
OSHA PEL	5 mg/m³ ceiling
NIOSH REL	1 mg/m³ TWA, 3 mg/m³ STEL
ACGIH TLV	0.02 mg/m³ respirable TWA, 0.1 mg/m³ inhalable TWA

Above 1 mg/m³, prolonged exposure can cause manganism, a permanent neurological syndrome called welder’s parkinsonism. The OSHA ceiling and ACGIH respirable TLV are far apart, so hood design matters more than the PEL. NIOSH also identified welder’s anthrax, a rare lung infection from metal fumes.

What to Write on the Sheet

One block per line item:

• Process and position, tied to the weld symbol.
• PPE: filter shade, gloves, jacket, footwear.
• Ventilation: type, hood distance, required cfm.
• Respiratory protection, or a note that controls suffice.
• Fire prevention: relocation or guarding, watch name and duration, extinguisher location.
• Hot work permit number and expiry, plus responsible person and date.

Tie it back to the drawing and the package is complete: symbol, procedure, and a safety sheet covering what must be in place before any arc is struck. Choosing the right electrode for the position changes amperage and shade, so safety travels with the consumable choice.

Turning the Diagram into Machine Settings: Amps, Volts, Wire Feed, and Heat Input

A weld symbol is a promise: this joint, this size, this process, this position. It never tells you “118 amps.” It points to a qualified procedure someone has proved, a range of settings that produces a sound, code-compliant weld. Land inside that range.

That range lives in the Welding Procedure Specification (WPS) and a qualification record. AWS codes such as D1.1 for structural steel and D1.6 for stainless set what a WPS contains and how it is qualified (AWS standards). Step outside the qualified amperage, voltage, or wire feed numbers and the weld is no longer the qualified weld.

Pick the Consumable by Thickness

Thickness first, then position, then the metal. A few shop rules of thumb:

Process	Amps to start
SMAW (stick)	About 1 amp per 0.001 in thickness
GMAW (MIG)	About 1 amp per 0.001 in thickness
GTAW (TIG)	About 60 to 80 amps per 0.001 in thickness

The TIG figure reads this way: a 1/16 in (1.6 mm) wall of stainless or aluminium sits around 60 to 80 amps. TIG feels gentle because the short arc and shielding gas keep the heat zone narrow. Filler rod runs from 3/32 in on light material to 1/8 in or 3/16 in for heavier sections.

For stick, the electrode chart:

Electrode	Operating range
1/16 in	20 to 40 amps
3/32 in	60 to 130 amps
1/8 in	80 to 150 amps
5/32 in	100 to 190 amps
1/4 in	130 to 225 amps

Operating windows, not targets: let the WPS settle the final pick. E6013 is the general-purpose all-around rod; E7018 is the low-hydrogen workhorse for inspected, structural, or higher-stress joints. The all-position welding rod guide decodes the rest of the numbering.

Stick stays the most forgiving process on site, wide amperage windows and no gas to manage, as argued in why SMAW still wins.

Volts Are a Consequence, Not a Setting

Process	Arc voltage window
SMAW	17 to 22 volts DC
GMAW	18 to 26 volts
FCAW	22 to 28 volts
GTAW	9 to 14 volts DCEN

On a constant current machine (stick, TIG) you set amps and voltage follows arc length. On a constant voltage machine (MIG, flux core) you set wire feed speed and the source trims voltage. Shielding gas shifts the number: a

Turning the Diagram into Machine Settings: Amps, Volts, Wire Feed, and Heat Input

A weld symbol is a promise: this joint, this size, this process, this position. It never tells you “118 amps.” It points to a qualified procedure someone has proved, a range of settings that produces a sound, code-compliant weld. Land inside that range.

That range lives in the Welding Procedure Specification (WPS) and a qualification record. AWS codes such as D1.1 for structural steel and D1.6 for stainless set what a WPS contains and how it is qualified (AWS standards). Step outside the qualified amperage, voltage, or wire feed numbers and the weld is no longer the qualified weld.

Pick the Consumable by Thickness

Thickness first, then position, then the metal. A few shop rules of thumb:

Process	Amps to start
SMAW (stick)	About 1 amp per 0.001 in thickness
GMAW (MIG)	About 1 amp per 0.001 in thickness
GTAW (TIG)	About 60 to 80 amps per 0.001 in thickness

The TIG figure reads this way: a 1/16 in (1.6 mm) wall of stainless or aluminium sits around 60 to 80 amps. TIG feels gentle because the short arc and shielding gas keep the heat zone narrow. Filler rod runs from 3/32 in on light material to 1/8 in or 3/16 in for heavier sections.

For stick, the electrode chart:

Electrode	Operating range
1/16 in	20 to 40 amps
3/32 in	60 to 130 amps
1/8 in	80 to 150 amps
5/32 in	100 to 190 amps
1/4 in	130 to 225 amps

Operating windows, not targets: let the WPS settle the final pick. E6013 is the general-purpose all-around rod; E7018 is the low-hydrogen workhorse for inspected, structural, or higher-stress joints. The all-position welding rod guide decodes the rest of the numbering.

Stick stays the most forgiving process on site, wide amperage windows and no gas to manage, as argued in why SMAW still wins.

Volts Are a Consequence, Not a Setting

Process	Arc voltage window
SMAW	17 to 22 volts DC
GMAW	18 to 26 volts
FCAW	22 to 28 volts
GTAW	9 to 14 volts DCEN

On a constant current machine (stick, TIG) you set amps and voltage follows arc length. On a constant voltage machine (MIG, flux core) you set wire feed speed and the source trims voltage. Shielding gas shifts the number: a CO2 or argon-dioxide mix needs more voltage than plain argon for the same wire diameter, and TIG’s short arc with helium or argon sits at the low end.

Polarity must match the consumable. Most SMAW and the common 75/25 mix on carbon steel run DCEP, electrode positive. GTAW on steel, stainless, and aluminium runs DCEN, electrode negative, concentrating heat in the work and keeping the tungsten cool. Reverse it and you fight spatter and a wandering arc. On aluminium MIG, that DCEN switch plus a push technique changes the job, as shown in the aluminium MIG welding guide.

Wire Feed Speed and Deposition Rate

On a CV machine, wire feed speed is the master control. It sets amperage, which sets penetration and fill speed. Wire size follows the plate: 0.030 in for sheet, 0.035 in for plate up to 1/4 in, 0.045 in for heavier sections. For steel:

Deposition rate (lb/hr) = WFS (ipm) × wire area (in²) × 60 × 0.283 (lb per cubic inch of steel)

Worked example: 0.035 in wire at 300 ipm. The cross-sectional area is about 0.00096 in², so 0.00096 × 300 = 0.288 in³ per minute, × 60 = 17.3 in³ per hour, × 0.283 = about 4.9 lb/hr, call it 5 lb/hr. That is a normal 300 ipm setup for 1/4 in carbon steel plate. Treat it as a ceiling: real deposition runs lower because of spatter and un-fused wire.

Heat Input: The Number That Governs Distortion

Heat input is the energy poured into each inch of joint, driving penetration, distortion, heat-affected zone size, and spatter. Field form for a fillet bead:

Heat input (kJ/in) = (volts × amps × 60 × duty cycle) ÷ (travel speed in ipm × 12)

Take a typical fillet: 20 volts, 120 amps, 60 percent duty cycle, 8 ipm travel. Substituting, (20 × 120 × 60 × 0.60) ÷ (8 × 12), gives roughly 1.5 kJ per inch of travel. Duty cycle accounts for arc-off time when you stop and restart. AWS code work expresses heat input in kJ per millimetre, so learn the conversion: 1 kJ/in is about 0.39 kJ/mm. TWI’s guidance on welding heat input walks through the method.

Push the number up and you get deeper penetration, a wider HAZ, more distortion, and more spatter. Bring it down and distortion eases, but travel too fast for the amperage gives a cold lap or lack of fusion. A technician who knows the number can diagnose a weld that just looks wrong.

Common Diagram and Welding Mistakes (and How to Troubleshoot Both)

A flawless weld fails inspection when the drawing is ambiguous, and a perfect drawing fails when the welder misreads it. Trouble rarely comes from one bad decision. It comes from a chain: a symbol was interpreted, that became a machine setting, and the setting produced a defect nobody traced back to the print.

Documentation mistakes

These live in the file, and they are the easiest to catch because nobody has to change a weld.

• Symbol on the wrong side of the joint. Reversing a symbol across the reference line swaps arrow side and other side, which physically relocates the weld. It is the most expensive drawing error, because it surfaces at assembly, not the bench.
• Missing weld size. A fillet symbol with no leg dimension says nothing about the finished joint. Under AWS A2.4 the dimension is the leg; older inch-based practice used the throat. Both conventions still circulate, so the drawing must say which governs. The current symbol standard lives in the AWS standards library.
• All-around confused with field weld. The circle at the arrow and reference junction means weld all around the joint; the flag at the tail means weld in the field. Swap them and you have sent a shop weld to the job site, or told the customer a shop weld covers the perimeter.
• Leg versus throat confusion on fillets. A 6 mm fillet means a 6 mm leg, not a 6 mm throat. Read under the wrong convention, the callout produces a weld roughly 30 percent smaller than intended, and it fails visual inspection against code.
• Missing units. A bare number with no unit note invites every shop to interpret it differently. State metric or inch on the drawing, and note the size convention.
• Symbol contradicting the WPS. A callout for a process or position the procedure does not cover is a paperwork failure waiting to become a rejected weld. The ASME BPVC and code-driven work treat the drawing and the qualified procedure as a matched pair.

Workmanship mistakes that start with misreading the drawing

Most weld defects are not mysteries. They are symptoms of a parameter that drifted from what the symbol required.

• Porosity: a dirty or coated surface, wrong shielding gas flow, excess voltage, or travel speed that outruns the gas coverage. Wind and moisture break up the shield too. Gas flow errors are covered in Air Gas Welding Explained.
• Undercut: amperage too high for the thickness, a long dragged arc, or a travel angle that pulls the arc forward over the toe.
• Lack of fusion: too little heat, travel too fast, the bead not placed on the root, or the arc held too far from the joint.
• Excessive penetration and burnthrough: too much heat for the joint, poor fit-up, or missing backing.
• Spatter: a long arc, polarity that does not suit the consumable, or coated and dirty base metal.
• Electrode stubbing: the electrode held at too steep an angle, or the work moving faster than the welder can feed. Matching rod to position helps; the All Position Welding Rod Guide covers the options.

Symptom, cause, fix

Symptom	Likely cause	What to change
Porosity, holes in bead	Dirty surface, low gas flow, excess voltage	Clean the joint, set flow per the WPS, lower voltage or speed
Undercut, groove along the toe	Excess amps, long arc, wrong travel angle	Trim amps, shorten the arc, hold a 10 to 15 degree drag
Lack of fusion, cold edges	Too little heat, travel too fast, poor bead placement	Slow travel, weave into the joint, land on prepared metal
Burn-through, root sag	Excess heat, no backing, wide gap	Reduce amps, close the gap, add backing
Spatter, popping beads	Long arc, wrong polarity, coated base metal	Shorten the arc, check DCEP or DCEN, clean the plate
Electrode stubbing, poor tie-in	Steep angle, feed too fast, wrong rod	Lower the angle, steady the feed, use a positional rod

The fastest root-cause path

Work the chain backwards: visible defect, then symbol, then the WPS parameter, then the machine setting, then the fix. Undercut in a 3G fillet is not automatically a heat problem. It is a question about which position code was on the drawing, what the WPS allows for 3G, and what the machine was set to. TWI’s welding defect resources are useful for the same reason.

Some problems are not parameter problems. Repeat cracking, a mislocated joint, distortion beyond tolerance, or a failed impact test needs engineering review and a code-compliant repair plan, not another pass with more heat. Regulatory expectations for inspection and repair still apply, but the fix comes from the engineer and the qualified procedure.

Fixing the drawing stops the defect from repeating on the next part. Fixing the machine stops it from repeating on the next one.

A Worked Example: From Drawing to Finished Weld, Plus Your Pre-Weld Checklist

Everything so far builds toward one moment: a bracket on a bench, a print in your hand, a bead that has to be right.

The Drawing

The job order calls for a 10 mm (roughly 3/8 inch) mild steel gusset bracket welded to a 12 mm base plate. The electric arc welding diagram shows a fillet symbol on the arrow side, a 6 mm size, a 100 mm length, process letter P (SMAW), position code 1F, and the note “WELD ALL AROUND BRACKET LEG, UNLESS NOTED OTHERWISE.”

Read the symbol basics in this order:

1. Arrow side: the fillet goes on the bracket side of the joint because the arrow points at the bracket leg. The arrow identifies the joint, not the metal.
2. Basic symbol: the right triangle, meaning fillet weld.
3. Size: 6 mm, which under AWS A2.4 is leg length, not throat. Older inch-based shop practice converts to throat size.
4. Length: 100 mm of weld, so the bead does not run the full leg.
5. Process letter: P, below the reference line, meaning shielded metal arc welding, or stick welding.
6. Position code: 1F, also below the reference line, flat and horizontal position with the fillet symbol.
7. Supplementary symbols: none, so no contour or melt-through requirement.
8. Note: the all-around instruction comes from the note, not a circle on the symbol, so both must be reconciled before welding.

Process, Consumable, and Machine

SMAW means a constant-current stick machine and a stick electrode. For a 6 mm fillet on 10 mm material, an E7018 at 3/32 inch is a sensible default. Operating ranges vary by manufacturer, so confirm against the electrode specification sheet or a guide like this all-position welding rod reference before you dial in amps. A 3/32 inch E6013 runs roughly 60 to 130 amps, a 1/8 inch E7018 roughly 80 to 150 amps, and about 1 amp per 0.001 inch of thickness puts 10 mm steel near 110 amps to start.

Arc voltage on SMAW is not a dial setting. It results from arc length, typically 17 to 22 volts DC, controlled by stick angle and travel speed. The WPS gives the amperage range; the inspection plan confirms the weld meets the AWS structural steel code D1.1 for structural welding practice and inspection in the United States. Stainless falls under D1.6, aluminium under D1.2.

Change the process letter and the setup changes with it: GTAW means DCEN, tungsten, and roughly 9 to 14 volts, while FCAW means a flux-cored gun on a constant-voltage machine. The symbol decides the shop.

Fit-Up, PPE, Ventilation, and the Bead

Clean the joint to bright metal, confirm the fit-up gap matches the WPS, and fixture the plate so the weld lands in flat or horizontal position to match 1F. A 3F code would change the approach, so confirm the setup matches the drawing.

PPE comes from the shade table in OSHA 1910.252, where shade 10 is listed for SMAW with 3/32 inch electrodes. Ventilation depends on the space: 1910.253 calls for mechanical ventilation where the volume per welder is under 10,000 cubic feet, in rooms with ceilings under 16 feet, and in confined spaces, at a minimum 2,000 cubic feet per minute per welder. A rolling hood near the arc usually handles it. Frame the hot work, move combustibles, and assign a fire watch per the NFPA 51B hot work requirements.

Then run the bead: short stringers, consistent 6 mm legs, no wandering arc, no craters at the ends. Clean between passes, check for undercut and porosity, and document the result. Under pressure equipment, ASME BPVC Section IX governs welder and procedure qualification.

Your Printable Pre-Weld Checklist

Stage	Check
Drawing verification	Correct print and revision on site; units stated; note and symbol reconciled; no conflicting marks
Symbol interpretation	Arrow and other side identified; basic symbol named; leg versus throat confirmed; length and spacing read
Consumable and machine	Process letter matched to machine type; electrode or wire classification matches the WPS; amperage range confirmed
Fit-up	Joint prepared to WPS; root gap, root face, misalignment within tolerance; fixture set
PPE and ventilation	Correct filter shade; respirator assessed for the material; extraction or hood in place; screens set
Hot work permit and fire watch	Permit signed; combustibles moved 35 feet or guarded; cylinder staged; fire watch assigned, remaining 30 minutes after work stops
Inspection and records	Visual inspection per code; welder qualification current; WPS and report filed with the drawing revision

Those records protect you months later: the drawing revision, the WPS, the welder qualification, and the inspection report together document what was actually done. Without all four, you have a weld and a guess.

What Comes Next

Reading symbols is a career skill, not paperwork trivia. It ties to qualification testing, code compliance under D1.1 and Section IX, and your value on the floor. Go deeper with the AWS certification and education pathways, then get hands-on practice rather than classroom theory alone. A TWI-style course turns a symbol into a repeatable weld, and learning to draw it lets you fix errors before they become rework orders.

Frequently Asked Questions

What is the difference between a welding diagram and a weld symbol?

A weld symbol is the compact graphic notation placed on a drawing to specify a weld; a welding diagram is the larger drawing that shows the assembly, the joints, and those symbols in context. The symbol is the shorthand inside the diagram.

Which side of a joint does the arrow side refer to?

The arrow side is the side of the joint that the arrow points toward when the arrow crosses the reference line. Any symbol placed on the arrow side of the reference line applies to that member, and reversing the symbol changes the meaning entirely.

What does a triangle on a welding symbol mean, and what number goes beside it?

A triangle is the basic fillet weld symbol. The number to its left is the fillet size, expressed as the leg length under AWS A2.4 practice, while some older documents specify the throat size, which is a frequent source of disputes on older drawings.

What do the circle and the flag mean on a weld symbol?

A circle at the junction of the arrow and reference line means weld all around. A flag at the arrow side of the reference line means the weld is a field weld, made on site rather than in the shop.

Do I need a welding diagram for a small shop repair?

A full engineering diagram is rarely required for a minor repair, but a hot work permit and a documented safe welding plan still are. OSHA 1910.252 requires fire precautions, a fire watch when listed conditions exist, proper eye protection, and ventilation whenever you are welding indoors in a space under 10,000 cubic feet per welder.

What ventilation does OSHA require for arc welding?

Mechanical ventilation is required when the welding space is under 10,000 cubic feet per welder, when the ceiling is under 16 feet, in confined spaces, or where cross-ventilation is obstructed, at a minimum of 2,000 cubic feet per minute per welder. Local exhaust hoods must hold 100 linear feet per minute at the welding zone, with airflow increasing as the hood moves away from the arc.

How do I set the welding machine from a weld symbol?

The symbol tells you the joint type, process, position, size and length. From there, match the consumable and amperage to the material thickness (a common starting point is about 1 amp per 0.001 inch for SMAW and GMAW, and 60 to 80 amps per 0.001 inch for GTAW), then confirm the settings fall inside the range of your qualified WPS.

What do the letters under the weld symbol stand for?

They identify the welding process: S for SMAW (stick), M or MA for GMAW (MIG), F or FA for FCAW, W or GT for GTAW (TIG), and SA for submerged arc welding. Position codes such as 3G or 1F usually sit alongside them and indicate where the welder must hold the torch.

Do welding symbols always follow the same standard?

In practice, drawings in the United States are usually drawn to AWS A2.4, which is closely aligned with the international symbol system in ISO 2553, and it looks familiar on drawings from other countries. Always confirm the governing standard noted on the drawing before interpreting a symbol.