Arc Weld – Tutorial

 

 

 

 

 

 

 

 

How to Arc Weld – Tutorial

This tutorial is intended to offer practical advice to beginner arc welders. It was produced with a great deal of help and guidance from professional welders whose time was funded by forum members and supporters. Take the tutorial slowly and practice the work covered on each page before moving onto the next.

Arc welding (short for Manual Metal Arc (MMA) welding and also known as Stick and SMAW) is a very involved subject and we only cover enough to get you up to speed. There are many books on the subject, and more detailed information can be found elsewhere on the internet. Also we have a very friendly forum that can help.

Arc Welding Safety

As with any other electric welding process, skin and eyes need to be properly protected from UV light. Electric shock, fumes, burns, and fire are other risks.

The safety page discusses how to minimise these risks.

Arc welding safety

Starting the Arc

The arc is started by touching the electrode momentarily against the work to complete the electrical circuit before raising the electrode to establish the arc.

‘Tap starting’ and ‘scratch starting’ are the two common methods of starting the arc. Which one to use is a personal preference, and can be influenced by rod and welder type. Both techniques are illustrated with videos on this page.

Starting the arc

Rod Position, Arc Length and Movement

The basics of arc welding are covered on this page with practice laying beads in the flat position.

Rod angle, arc length, travel speed and welding motion are illustrated with photos and videos, and a video shows the effect of varying the arc length.

Rod angle, arc length and motion

Arc welding faults

When learning any new process you’ll likely start off doing things wrong. Profiles and sections of welds with various faults are compared with good welds on this page.

The faults covered are incorrect travel speed, incorrect arc length, and incorrect amps.

Arc welding faults

Flat Joints and Joint Preparation

Arc welding is especially suitable for joining thick material as cold joins are easy to avoid. That makes it possible to tackle thicker material using multiple passes of weld.

This page covers joint preparation and techniques used in multiple pass arc welding.

Flat Joints and joint prep

Fillet Joints

Having spent time getting the root weld right on the previous page you’ll find fillet welding a breeze.

Multiple passes are also commonly used in fillet joints. This page covers rod angle, weld sequence, and a little joint design.

Arc welding fillet joints

Buying an Arc Welder

For most people a DC inverter is the best type of arc welder to go for. They have many advantages over the older types, but can fall down on repair costs and longevity.

The page covers what to look for in inverter welders and other types of arc welder.

Buying an Arc Welder

Other Types of Arc Welder

Arc welding has been around for a while, and there are big differences between the technologies used in older secondhand welders and new ones.

This page discusses the pros and cons of different types of arc welder.

Types of arc welder

Welding Different Steels

How to weld just about anything from a nuclear power station to a bicycle frame!

This section summarises the welding procedures and consumables that might be used to weld the more widely used types of steel including Mild Steel, Corten, Weldox, Hardox, Stainless Steel, Chrome Moly, EN19, EN24/EN24T, EN8, Cast Iron, Cast and Manganese Steels, Wrought Iron, and Hardfacing. There is also a page explaining hydrogen embrittlement.

Welding DIfferent Steels

More Soon:

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Arc Welding Safety

This is not a comprehensive guide. There are many ways in which welding can damage your health. The main points are:

  • Protect skin and eyes from UV light, and shield your welding area from the eyes of onlookers.
  • Work in a well ventilated area (extraction fans should be used when welding inside a workshop) A vapour mask or an air fed helmet are required for special materials.
  • Be careful not to leave anything flammable nearby. Welding spatter and grinding sparks can travel a long distance.
  • Slag can ping off a hot weld and burn into your eyes. Use safety glasses or goggles.

Arc UV Light

Arc welding tends to be used for thick metal at high amps, so the light generated by the arc is very bright. Any exposed skin will become sunburned quickly so overalls and welding gauntlets (gloves) are a must.

Looking directly at a welding arc even for a short time causes arc eye where the UV from the arc burns the cornea. Expect to be awake all night with the sensation that someone is sticking pins in your eye. Also warn others in the area not to look at the arc and keep the welding area screened from public view.

Auto-darkening helmets are very useful for arc welding – with fixed shade helmets is difficult to judge where the end of the rod will first make contact with the work. A shade between around 10 and 12 would be suitable for arc.

Fumes

Welding fume (in total) should be controlled to ensure there is less than 5mg per cubic metre of clean air. This is surpisingly little and very easy to exceed.

Even the fumes from 6013 mild steel rods can be harmful if breathed in regularly. The best advice is to avoid as much as possible. Keep the work area well ventilated, and keep your head out of the fumes.

Being a flux shielded process it is possible to arc weld in a strong breeze, so extraction can be added close to the welding area.

For galvanised metal, stainless steel and hardfacing alloys (in fact anything other than mild steel) at least a fume mask should be used, preferably an air fed helmet, in addition to ventilation.

Some rods have fluorine coatings and these these require very careful precautions against fumes.(E 7018 contain flourine). Some cast iron rods contain Barium which should also be avoided as much as is possible. (Gasless wires can also contain Barium).

Some degreases also contain flourine

Always ask for and read the manufacturers instructions and HSE guidance (http://www.hse.gov.uk/welding/index.htm). Manufacturers are legally obliged to inform you of any hazards and to supply Material Safety Data Sheets for all their products.

Spatter

There can be a lot of sparks and spatter flying around especially when learning to arc weld. Cotton overalls are more resistant to spatter than man made fabrics, and leather aprons offer excellent protection. Spatter down the neck or shoes can be especially annoying. A welding cap can help protect the head when overhead welding.

The welding area should be cleared of inflammable materials. Fires can be difficult to notice while wearing a welding helmet.

Keep a fire extinguisher nearby – Both CO2 and dry powder types are suitable. Any type that contains water (foam or water types) should not be used near mains powered electrical equipment.

Electric Shock

DC arc welders run at about 80V so can give an electric shock. AC welders set to 80V will have a peak current near 120V, so the risk and potential danger of a shock is higher.

For a shock you would need to bridge between the electrode and the earth return. Minimise the extent of live parts by making sure all cables are in good condition (with no bare insulation or frayed wires), and that the rod holder is insulated. Welding gauntlets will help insulate only when they are dry – they can become damp with sweat.

The shock from an arc welder can be a fair jolt but is unlikely to be life threatening (unless you are also working on top of a tall building or have other health problems.)

Slag

Don’t look closely at the weld while it cools – as the weld contracts tiny hot pieces of slag can ping off and burn themselves into your eyes. This is especially true of stainless rods.

Slag is lightweight and brittle so can fly a fair distance. Wear eye protection when chipping.

Common sense (a disclaimer)

Use your common sense when welding. This page may not be comprehensive. Take advice from your welding supplier and experienced welders before starting to weld. See the more detailed disclaimer too.

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Starting the Arc

Arc welders don’t have a button to start the arc. Unlike MIG welders the rod (electrode) will become live as soon as the machine is switched on.

The arc is started by touching the electrode momentarily against the work to complete the electrical circuit before raising the electrode to establish the arc. This needs to happen quickly to avoid welding the rod to the work. “Tap Starting” and “Scratch Starting” are the two common methods of starting the arc.

Because the rod is live at all times it needs to be kept insulated from the earth when not in use. In the photo the welding bench is earthed, and a piece of wood is being used to isolate the rod from the bench. After welding the rod is returned to the piece of wood.

Rod resting on insulated pad

Tap Starting

A sharp tap of the rod against the work will remove excess flux from the end of the rod and create the electrical contact needed to start the arc.

A sharp wrist action should allow a momentary contact with the work before quickly pulling the rod a short distance away. Too heavy a contact or too slow an action can cause the rod to stick.

In the video the auto-darkening helmet darkens as soon as the arc is started. The light is bright at first because the arc length is initially too long. The arc length is quickly reduced to the correct distance for welding.

Rods start much more easily on the second attempt. It is good practice to first start the arc on some scrap material before starting the arc at the beginning of a weld.

2.5Mb Flash video preloads before playing and includes sound.

Scratch Starting

An alternative starting method is to lightly scratch the rod against the work. Moving the rod against the work removes excess flux from the rod and allows electrical contact from the steel in the middle. As soon as the rod starts to spark it is lifted from the work to start the arc.

In the video a backwards and forwards scratching motion is used to remove the flux coating. A limited movement should mean the arc will start somewhere close to where you want to start welding. When the first spark is seen the rod is pulled away from the work to prevent sticking, and then it is returned to the normal arc length for welding.

The scratch start technique is more prone to sticking as it relies on human reaction times. It can be a useful technique for difficult to start rods, or for AC machines and those with low open circuit voltage which make Tap Starting more difficult.

Excessive pressure on the rod while scratching will increase it’s chances of sticking.

3.9Mb Flash video preloads before playing and includes sound.

Rods Sticking to the Work

If you are new to arc welding you will frequently stick the rod to the work when trying to start the arc. The rod welds itself to the work and it won’t be possible to remove it just by pulling. Moving the rod backwards and forwards, or twisting the rod should fatigue the joint allowing you to remove the rod. If you have a crocodile clip type electrode holder you can just release the rod from the holder.

There’s no need to panic when the rod sticks. It’s normal for rods to stick occasionally, so arc welders are designed to cope with it for a short time. Inverter welders will reduce voltage automatically, and transformer welders should only go up in smoke if the rod is stuck for a prolonged period.

For interest, the photo shows the electrode of a 7018 rod recessed into the flux coating after welding – it illustrates why the flux coating needs to be removed before the arc will start.

Electrode recessed into flux

A tip to make starting much easier

Keep some scrap material near the work and start the rod on that before beginning your weld. This will remove excess flux and warm up the rod which will make it much easier to start your weld.

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Learning to Arc Weld – Basic Technique

Arc welding takes some effort to learn, and it is very sensitive to the position of the work. It’s a good idea to keep things easy to begin with by laying beads on the flat. We’ll cover joints later.

The following setup is a good starting point for this tutorial:

  • Work: 6mm mild steel. Arc welding is more tolerant to slightly rusty metal and mill scale than other electric welding processes, but it is good practice to clean the worst off with a grinder before welding.
  • Rods: 3.2mm 6013 rods. USE GOOD QUALITY RODS! A forum member trying to learn with DIY store rods had terrible trouble until someone sent him a few brand name rods to prove a point. Also 3.2mm rods are easier to learn with than 2.5mm rods.
  • Amps: 110 amps. (if you want to use 2.5mm rods reduce the current to about 80 amps – the current is determined more by the rod size than the thickness of sheet).
  • Polarity: DCEP (rod positive, earth negative – this is the opposite of the polarity used in TIG). Use AC if that’s all you have.

That’s what we’ve used over the next couple of pages. You can compare your practice with our efforts, in particular with the fault finding guide on the next page. Not all welders have perfectly calibrated amps, so you may need to adjust yours to avoid faults.

Rod Angle (lead angle)

For welding on the flat (as in the photo) the rod should be angled 10 to 20 degrees from vertical and pulled in the direction of the arrow. The angle of the rod prevents the slag overtaking the rod (welding over slag would cause inclusions in the weld).

In the photograph the rod has been bent at the electrode holder to position the holder at a more comfortable angle.

It’s OK to support the top of the electrode with your spare hand and this improves control of the electrode. Electric shocks aren’t a problem, but be careful to reposition your hand away from the heat before the electrode gets too short.

Rod Angle

Arc Length

The arc length is the distance between the electrode and the weld pool. It should be roughly the same as the diameter of the rod.

This is nowhere near as straightforward as it sounds!

The photo shows how the electrode becomes recessed inside the flux covering on the rod. The weld pool will also be hidden by molten slag.

To achieve the correct arc length using 3.2mm rods the distance between the flux coating on the rod and the flux on top of the weld might be less than 1mm.

Arc welding electrode recessed in flux coating
The arc length is normally judged by the sound and visible light from the arc.

In the video the arc length is varied between correct, too long, and too short. Both the intensity of light and the sound of the weld alter dramatically with the length of the arc.

The arc should be kept short and hide the majority of the light from the weld without pushing the rod into the slag pool. A good short arc length will result in a consistent sharp crackling sound.

The appearance of the completed weld will provide further clues – see photos of welds with incorrect arc length on the faults page.

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Maintaining Lead Angle and Arc Length

The rod becomes shorter as the weld progresses, and it takes a conscious effort to reduce the length of the arc as the rod gets shorter. Excess arc length can lead to an unstable arc, excess heat and undercutting and is probably the most common beginner fault.

The angle of the rod should also be maintained over the length of the weld. A little practice is required to avoid decreasing the lead angle as the weld progresses, as this can result in slag inclusions and even cause the arc to stall. The easy way to maintain rod angle is to focus attention on moving the rod holder rather than the rod as the weld progresses.

The video shows a 2.5mm rod being consumed while running a bead around 200mm long.

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Welding Motion

For most arc welding the rod is moved in a straight line to form a “stringer”. A tiny amount of weave can be used to help control speed and direction.

In the video the arc is started with a tap start. The rod quickly becomes shorter as the weld progresses and the motion that can be seen is constant correction to maintain a short arc length.

Note the rod angle is also maintained. It takes practice to maintain arc length and rod angle, especially if you are moving to arc welding from another welding process.

 

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Slag

Don’t look closely at a hot weld – bits of slag continuously ping off the weld as it cools and it is very painful to have them removed after they’ve burned themselves into your eye. Eye protection is also a good idea when chipping slag as it’s brittle and can fly a fair distance.

The slag covering the weld should be reasonably easy to remove, though it does depend on the type and quality of rods (we were using some good quality 6013 rods here so it was easy).

Weld with slag

Practice makes pads

Other positions will go disappointingly badly before you have perfected laying beads. A good way to practice is to weld a pad on 6mm plate.

Clean the plate thoroughly, then lay the first weld in a straight line near the edge of the plate. Remove the slag and lay a second weld immediately to the side of the first, close enough so the two welds merge together with no gap. Repeating several times should result in a pad of welds with a flat top. If you struggle maintaining a straight line then drawing a line in chalk might help.

Turn the pad 90 degrees and weld the next layer of the pad.

In college training the pad would be sectioned to check for inclusions in the weld. The practice helps develop consistency, keeping the weld in a straight line, and is good preparation for thicker metal where the joint is often formed from multiple strings of weld. The technique is also used for hard facing and building up worn material.
 
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Arc Welding Faults

The faults in these photographs are a little exaggerated. Your own faults may show some of these characteristics, but hopefully won’t be quite as bad as the ones we managed. If they are it might be worth another read of the learning arc welding page.

Arc Length Faults


There’s some detailed information including a video demonstrating the effect of arc length on the learning arc welding page. Beginners will commonly have too long an arc length and too great a lead angle. Note that an excessive rod lead angle will also increase the arc length.

  • Arc Length Too Short
    This weld was laid with the end of the rod covered by the molten slag. The surface of the weld is uneven where it has been dragged along by the rod, and the weld will be low on power and contain slag inclusions.
  • Arc Length OK
    A normal arc weld. The weld has a consistent profile and minimal spatter.
  • Arc Length Too Long
    Too great a distance between the rod and the work will increase the voltage resulting in a flat and wide weld with a great deal of spatter. It also makes the arc unstable, and the slag will be difficult to remove from the edges of the weld. Sectioning this weld reveals undercutting to the left side.

Arc welding is a constant current process, but the arc length has an effect on voltage. Reducing the arc length will decrease the voltage, and this reduces the heat in the weld. Increasing arc length will increase the voltage. Arc length faults can share many similarities with the current faults later on this page.

Arc length faults - too short, normal and too long

Arc length faults - sectioned welds

Travel Speed Faults


Beginner welders tend to move the rod too quickly, especially those who are transitioning to arc welding from another welding process. The pool of molten slag is wide, tall and bubbly, and shouldn’t be mistaken for the weld pool!

The weld underneath the slag will be about half the width of the molten slag pool, and it takes longer than might be expected to build it up. Experienced arc welders say they can see the weld through the slag pool (they say it is darker and more red in colour).

  • Speed OK
    The bead is fairly consistent. The ridges in the weld are semi-circular.
  • Speed Too Fast
    Excessive speed results in a thin, weak bead. The ridges in the weld are elongated and triangular. Had the current been increased to compensate for the speed the ridges would still remain elongated.
  • Speed Too Slow
    Welding too slowly results in a wide tall build up of weld. The shape of the weld is not consistent as the weld pool has built up and then collapsed into the crater. The poor control of the weld pool can result in cold joints and slag inclusions.
Arc welding travel speed faults

Arc travel speed faults - sectoned weld

Current Setting Faults


Welding rod boxes are marked with their recommended current. For my 6013 Murex rods the 2.5mm rods are marked 70 to 100 amps DC, and the 3.2mm rods are 100 to 140 amps DC.

Where in the range you work will depend on the position of the work, but for beginners setting the amps right in the middle of the range should rule out most faults due to incorrect amps.

  • Amps too low
    Setting the amps too low will result in a tall, narrow bead lacking in penetration. The weld will be difficult to start and the arc prone to straying towards one side of a joint in preference to the other.
  • Amps too high
    The bead is wide, flat and irregular, and a small undercut can be seen on the right of the weld in the sectioned photo. A deep crater has formed at the end of the weld, and the slag is difficult to remove from the edges of the weld.
    Excessive current should not be compensated by excessive travel speed. This can result in slag inclusions due to rapid cooling of the weld.
  • Amps OK
    With the amps set correctly the bead is a consistent rounded shape, and the slag is easy to remove.
Arc welding current setting faults

Sectioned weld showing current setting faults

 
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Arc (MMA) Tutorial – Flat Joints

The principle of welding joints in thick metal differs slightly between MIG and Arc welding. With MIG welding it is the heat of the weld pool formed by molten filler wire which melts the parent metal to form the weld, so power needs to be increased with increasing metal thickness to prevent the weld pool from freezing before it can penetrate.

In Arc welding, the arc melts a crater into the parent metal creating the weld pool and filler from the rod is mixed in. This makes it much less prone to cold joints than MIG, and allows thick metal to be welded in multiple passes without the need to increase amps or rod size. ‘Flat joint’ just means the work is flat on a bench and is welded from above. It’s also known as ‘1G’ position. Horizontal and vertical joints will be covered later on.

Accurate joint preparation is very important in arc welding. It is very difficult to weld joints with large or uneven gaps.

Square butt joint (joint without preparation)

The photo shows a 6mm plate butt welded using exactly the same technique as in the video on the learning arc page. The two plates were positioned tightly together, and 3.2mm 6013 rods were used at 120 amps.

Penetration is poor reaching only 1.5mm into the plate. Added to the thickness of the weld bead the total thickness of the weld is about 4mm so it will be a lot weaker than the surrounding plate.

While it would be possible to increase penetration by increasing rod diameter and current, it is more efficient to prepare the joint.

Square butt joint

Joint Preparation

A “Single Vee Butt Joint” is a common way to prepare thicker metal when a full penetration joint is required. A 60 degree V (30 degrees on each side) is ground into the two plates.

The V doesn’t extend to the bottom of the plates – a root face is left. This is normally about the same height as the rod diameter (2.5mm in our case) and reduces the chance of blowing holes.

To aid penetration the two plates are spaced apart. We’ve used a TIG rod as a gauge to form a 2.5mm root gap (again the same as the rod diameter). Different welders will have their own preferences for joint preparation.

The volume of filler metal required to fill the vee joint is greater than can be added in a single pass, so several passes are required. These are described below.

Sinvle vee butt joint preparation

Root Pass

The first pass is the root pass. This is intended to fully penetrate to the rear face of the joint. We used 2.5mm rods (these run at lower amps than 3.2mm rods so reduce the chance of blowing holes). Around 70 amps is a good starting point, but if you find yourself blowing holes try slightly lower amps or adjust the root gap.

The root weld is easily the trickiest weld we’ve covered so far. It’s similar to welding thin metal which is something arc welding isn’t well suited to. There is a very fine balance between insufficient penetration and blowing holes. A consistent tight arc is important as that will keep the heat low, and a very controlled movement is necessary, speeding up a little as the plate warms up. A very slight weave can help control the arc.

We ran out of rod halfway through the root pass. The weld has been ground back at a gentle taper. We started the next rod at the start of the taper, so by the time it reached the gap it was hot enough for full penetration. The transition was ground to the level of the surrounding weld prior to the next passes.

Root weld ground out at end

Root Penetration

It takes very accurate technique to avoid blowing holes. (Spend a day practicing root welds and the rest of your arc welding will move on enormously). Signs that a hole is about to blow through are a little keyhole that opening up in front of the rod and a hollow sound to the arc. Holes can be countered by reducing the arc gap and then speeding up a little to avoid new ones.

If you do struggle with holes then reducing the root gap a little will make the root very much less sensitive to amps and technique at the risk of reduced penetration.

We cheated and avoided blowing holes by using a welding bench under the work as a heat sink. We were running a little hot so our penetration is a little wide. Without the cooling effect of the welding bench we would have blown a hole. It is common to use TIG for the root as it’s a lot easier to control and less cleaning up is necessary afterwards.

Root penetration with backing heat sink

Split Cap

The root weld needs to be completely cleaned of slag before subsequent passes, and any unevenness smoothed out with an angle grinder, else subsequent welds will also be uneven.

Our weld was finished with two further stringers laid with 3.2mm rods at about 110 amps. A stringer is a bead welded without any side to side weaving. These are a lot easier than root welding as with the root in place there is no longer much risk of blowing holes.

The diagram to the right shows roughly what we were trying to achieve. After the root weld (1) was cleaned up a single stringer with a slight weave was made to form half of the weld (2), then a second stringer used to complete the weld (3).

Diagram showing weld positions in split cap
The angle of our joint was a little wide and we didn’t quite fill the joint. A 60 degree joint would be easier to fill, and we could have reduced amps a little or weaved a little more to increase fill.

The technique can be adapted for thicker material – had we been welding 12mm plate we would have added a further 3 stringers on top to complete the weld.

At the bottom of the 3rd pass there is a slag inclusion. This is probably due to slag not properly cleaned from the edge of the root or second pass. A good wire brush would have removed the slag at the edge of the weld that chipping didn’t remove, or an angle grinder could have been used to clean the weld between passes.

Completed Vee butt weld

Weaving Capping Weld

It is possible to increase the fill rate of the rod by using a weaving motion. In the video a single weaving cap weld is used to complete a single vee joint. A slightly curved side to side motion is used to widen the weld and increase the fill. The direction is reversed when the arc reaches the edge of the V.

The flux covering the weld will make the weld appear wider than it really is. It can be tricky to judge the width of weave necessary. One trick is to draw two chalk lines on some scrap, try to weave between the chalk lines leaving the weld at the edge, then remove the slag and see how close you got.

An alternative motion is a “figure of eight”. This can help regulate speed, concentrates the arc on the edges of the weld, and tends to result in a higher fill.

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The Completed Cap

The cap weld is wider and lower than a single bead. Had the other side of the joint been prepared and welded in a similar manner the joint would have had close to full penetration.

The advantage of welding both sides is it reduces distortion and reduces the number of passes required for complete penetration. The capping weld will shrink as it cools and pull the work into a bend. If the plate was welded from both sides the weld on the reverse would tend to straighten the work.

Weaving cap weld
 
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Arc (MMA) Tutorial – Fillet Joints

Arc welded fillet joints are rarely intended to be full penetration joints. Joint preparation (as seen on the butt weld page) is not normally carried out, and the strength of the fillet weld is in the thickness of the weld itself rather than the depth of penetration. A similar technique is used to weld overlap joints.

When welding two plates of metal at an angle the rod should bisect the angle of the plates so that heat is distributed evenly into both plates.

There should also be a little lead angle on the rod as described in the learning arc welding page (ignore the shadow cast by the rod in the video as the position of the light makes it misleading).

We’ve used a 3.2mm rod running at about 100 amps for the root weld in the video. A tight arc helps keep the heat focused in the corner of the joint, and also prevents the arc from straying towards one plate or the other.

1.3Mb 48s Flash video preloads before playing and includes sound.
There is a small hole half way along our root weld. This is where the welder changed position mid-run and moved the rod too close to one side – you can see it happen in the video above. The rod has arced against the nearest piece of metal, and avoided the furthest plate leaving a hole full of slag.

A tight arc and correct rod angle should avoid this. The flux has nowhere to go in the corner, so more of the visible light from the arc is hidden by the flux. A very slight weaving motion can be used to help control motion, but it shouldn’t be excessive as the aim is to heat the inside of the corner.

The neatness of the root weld will determine the neatness of subsequent welds.

MMA fillet root weld
The root weld above will not be as strong as the parent metal. The weld doesn’t penetrate very far into the corner, so the majority of the strength of the weld is in the thickness of the filler material. The strength of the weld is determined by the throat thickness which is the minimum thickness of the weld plus any penetration. This is difficult to measure so tends to be estimated as 0.7 x leg length for a flat profile ‘mitre’ fillet as in the photo.

As with flat joints multiple stringers are used to increase the material in the weld for plate thicker than about 6mm. Stringers are beads layed with no weave. The number of runs will depend on application, but throat thickness will rarely need to be thicker than the plate.

The effects of gravity mean the horizontal leg length is slightly longer than the vertical leg. Angling the rod more towards the vertical plate will help to counter this as the filler metal and heat focus in the direction of the rod.

Diagram of three pass fillet weld
In the photo the root pass continues all of the way along the plate. the second pass was stopped before the end of the plate, and the third a little earlier just to help show how the weld is put together.

The second pass is made on the bottom of the plate as this gives something for the third pass to sit on. Both the second and third passes are centred roughly on the edge of the previous weld, and the same would be true if further passes were required.

Weld sequence in 3 pass fillet weld
There is a slight undercut at the top of the third pass where the edge of the weld has cut into the parent metal. Undercutting is caused by excessive amps (see the faults page) and causes a stress concentration at the edge of the weld.

In our case the undercut was caused by the third run being made when the metal was still hot from the second. The second pass has no undercut.

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Buying an Arc Welder

Arc welding is only really suitable for metal over about 3mm. It can be used down to 2mm but becomes very fiddly and difficult to control. It’s no good at all for welding cars! For metal below 3mm a MIG or TIG welder would be more suitable.

Arc welding is a strong and economic way to join thicker materials, especially when restricted to a domestic power supply. Where a MIG welder would require an increased power output for thicker materials, an smaller arc welder can often be used by increasing the number of passes instead of increasing the amps.

Which Welder to buy?

For the majority of people (those who don’t have any special requirements) a DC inverter is the best type of arc welder to look for. They are the easiest type of arc welder to use, portable, and less demanding on power supplies than other types of arc welder.

Even the cheapest Chinese inverter welders perform reasonably well, but at the time of writing (2010) they aren’t known for their reliability or support. There are many reports on the forum of cheap inverter welders failing within a few weeks of purchase. eBay tends to be the source and warranties can be tricky on there. Chinese made welders are best purchased from established UK based suppliers who can satisfy the warranty. It is in the interest of these suppliers to supply half decent ones to save on warranty claims.

Inverter welders do go wrong – they can be sensitive to knocks, power surges from the mains, dust and internal corrosion. Repairs will often cost more than the welder cost to buy in the first place. The difference between Chinese and European made inverters tends to be how sensitive they are to damage. And as a result how long they last.

Arc welding

What about TIG?

The power source used in arc welders is very similar to the one used in TIG welders, and most (if not all) TIG welders can also be used for arc welding with the addition of a rod holder.

It doesn’t work the other way around. TIG requires some extra features – a gas valve and HF start (an easy starting method that avoids tungsten contamination). If you also want to TIG weld it’s best to start off looking at welders that are sold as TIG welders.

In more detail – what to look for?

  • AC or DC?
    DC is easier to start, and is safer than AC as the peak voltage is lower. Most rods can be run on DC.
  • Open circuit voltage (OCV)
    Cheaper welders will tend to have 50V OCV which will make them more difficult to start, make the arc less stable, and prevent the use of special rods. Most decent transformer machines and inverters will run 70-80V and these are the ones to look for.
  • Start current, crater fill and fancy stuff
    Many DC machines, and most inverters will increase the current when starting the arc. It’s a useful feature to have as it makes it much easier to start the arc. Inverters often have crater fill which adds a little extra metal to fill the crater that is left is you pull the rod away to finish welding.
  • Maximum amps
    An output of 140 amps is at the limit of a 13 amp 240V supply (for inverter machines). This will allow the use of 3.2mm rods. (100 amps output would be needed to run 2.5mm rods, and rods smaller than 2.5mm would require a lot more skill to use).
    Higher outputs will allow the use of thicker rods which will reduce the number of passes required on thicker materials.
  • Duty cycle*
    Some of the air cooled transformer arc welders have a very low duty cycle and can burn only one or two rods at full power before needing a long cooling period. Most other types should have an adequate duty cycle.
  • Display
    For beginners it’s very useful to have a digital amp readout to accurately set the amps. This helps rule out one of the variables in learning.

Aside from that the main choices are price, robustness, size, efficiency on a limited amp supply, and typical life time (which will depend on the quality and also on the type).

*More on Duty Cycles

The duty cycle of a welder normally reflects how long it can weld in a 10 minute period before it has to cool down. A 70% duty cycle would allow 7 minutes welding over a 10 minute period and the duty cycle will reduce as amps increase. It’s not easy to compare duty cycles in manufacturers specs as the standards for measuring it vary between manufacturers.

Some expensive welders will test themselves at an ambient temperature of 40 degrees, some will test at room temperature, and others prefer it chilly. Also the time the duty cycle is measured over will vary between manufacturers. 10 minutes is the normal standard, but the cheaper welders often go for 5 minutes, instantly doubling their duty cycle. Very cheap welders with low duty cycles won’t burn a rod before thermal cut out.

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Types of Arc Welder

Arc welding has been around for a long time, and there are now a number of distinct types of arc welder. This page discusses the pros, cons and typical characteristics of these different types of welder.

DC inverters

Unlike traditional arc welders, modern DC inverter arc welders are very small, light and portable. Even the cheap ones available from as little as £100 function well, though the more expensive ones (up to £500) will be much more robust and will normally last much longer.

Pros:

  • Very efficient – they can run up to about 140 amps on a 13 amp 240V supply, and tend to have have good duty cycles (you can weld for longer on higher settings).
  • Small, lightweight and very portable. Generally less than 10kg in weight.
  • DC output results in easy arc starting
  • Most inverters have features such as hot starting to improve the ease of starting, and a soft finish to reduce the crater at the end of a weld.
  • All but the cheapest have 70V or 80V OCV (open circuit voltage)
  • Most can be used for scratch start TIG. More expensive ones tend to have HF (high frequency) start functions for TIG welding.
  • Pricier ones have features such as “arc force” which adjusts the voltage on the fly to cope with dirty plate.

Cons:

  • Inverter machines are complex electronically, and repairs can be very expensive. The cheaper ones are sensitive to knocks and spikes in input voltage. The more expensive ones have more protection – some are designed to withstand being dropped from 0.5m.

Verdict:

DC inverters are the sensible buy for anyone new to arc welding. Even the cheapest ones tend to weld very nicely, the downside of the cheap ones being that cheap components that don’t last very well.

Lorch H150 Inverter welder

Inverter welder circuit board


AC/DC inverters

These are normally aimed at TIG welding, and would not be bought for arc welding alone, but they generally have arc welding settings.

Pros:

  • Some rods are AC only. An AC/DC inverter can be used with these.
  • AC is not susceptible to magnetism which can cause stray arcs on DC machines.
  • The TIG welding capabilities.

Cons:

  • Expense: For inverter welders the AC function takes a lot of electronics, so prices of half reasonable machines start at £1000.

Verdict:

Fantastic for ARC welding, but only buy one if you also need to TIG aluminium.

Lorch T220 Control Panel

DC transformer welders

Transformer based arc welders are normally very heavy, and are aimed at TIG welding in a workshop rather than portability.

Pros:

  • These are excellent quality welders – for ease of use they are only bettered by decent inverter welders.
  • Duty cycles tend to be higher than modern inverter welders, so these machines are still used by fabrication companies when they need to do long runs of weld at very high amps.
  • Can last for much longer than inverter based machines, and are easier and cheaper to repair if they do go wrong. Many are still in regular use after 30 years.
  • The TIG welding capabilities.

Cons:

  • Not Portable: A Syncrowave 300 weighs 330kg and is the size of a house.
  • The machines with huge power requirements – the Syncrowave manual recommends a 110 amp 240V supply.
  • The buzz from the enormous transformers and 2 foot diameter fans create a lot of noise.
  • Parts available for the older ones is becoming sketchy.

Verdict:

Buy one secondhand if you want something that will last and have the space to keep it.

Very large BOC TIG welder

AC oil cooled welders

Pros:

  • Very simple heavily built welders that should last for ever.
  • Normally have both 50V and 80V settings. Smooth consistent arc while welding.
  • Oil cooling results in an excellent duty cycle.
  • It is possible to pick them up cheaply secondhand.

Cons:

  • Not Portable: Oil cooled welders are very heavy, even small units can weigh in excess of 100kg.
  • Starting the arc in AC is more difficult than with DC welders.
  • Can’t be used for TIG welding.

Verdict:

Old school equipment that you should never need to replace. Buy one second hand if you are old school, but bear in mind they take a little more skill to use.

Oil cooled arc welder

AC air cooled welders

Often referred to as buzz boxes. A number of companies made reasonable quality air cooled AC welders in the past. The technology is now the reserve of DIY stores selling welders to people who don’t know any better. They are the least usable of any type of arc welder.

Pros:

  • Cheap! Most large DIY stores will sell them for as little as £50.

Cons:

  • They tend to have a low OCV (open circuit voltage), so starting an arc is tricky.
  • The low OCV results in an unstable arc, and this gets worse as the transformer heats up. While they will weld it is to a lower standard than any of the other types of ARC welder.
  • Can’t be used for special rods that require over 70V OCV (such as low hydrogen).
  • Very poor duty cycle: Many of the cheap ones will weld for only 30 seconds before needing a rest for 10 minutes on the maximum amp setting.
  • They are less efficient than inverter welders and will tend to require a dedicated supply to work on higher settings.
  • Can’t be used for TIG welding.

Verdict:

To a great extent these are a waste of money. They are the most difficult to use of any arc welder, so most DIY buyers will decide they don’t like the process and give up. The duty cycles are annoyingly low. They are only really suitable for someone who wants an arc welder for very occasional use and doesn’t want to spend money.

Cheap arc welder
 

 

 

 

 

 

 

 

 

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3 responses to “Arc Weld – Tutorial

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