A beginners guide to welding – choosing the right machine – Part 2

Penned by resident technical adviser “Assassin”, this is the 2nd and last part of a lengthy yet comprehensive 2-part article. It looks at MIG wire, dual purpose MIG and ARC machines, TIG welding and finally – selecting a welding plant. Main photo: Marcus Cleveland


Within this last part of the 2-part article about welders, please be aware it is being written with beginners in mind, so those more familiar with welding please be patient as it details how different machines work.

As before, I must emphasise – there are many types of welding ranging from specialised welding methods such as submerged arc to laser welding, you can even weld plastic with the right equipment, but for our purposes we will stick to ARC, MIG, and TIG welding as these are what we will use.

Part 2

Dual purpose machines give is the best of both worlds, it gives us the advantage of having MIG which is better on thinner material such as bodywork, the advantage or ARC which is better on dirty material and the cheaper form of welding combined in one machine. It gives us the advantage of switching between the two on a specific job such as a chassis repair where you use MIG but find the torch is too large to get in over the top of the chassis, you switch to arc, of if you run out of gas or MIG wire part way through a job you can switch to arc. You may run out of welding electrodes before a job is finished so you switch to MIG, either way you can complete a job as you have options.

Inverter sets have another massive advantage and most manufacturers of quality machines will state this as it is its capability to work off a domestic socket, mine will run at up to around 160 amps from a standard mains socket which is another bonus if you want a portable unit. For power outputs exceeding 160 amp you need a standard 240V round industrial plug of 32 amps rating for my 250 amp unit, if you get a 32 amp socket and a short piece of suitable cable and a domestic mains plug you can make an adapter to allow you to run from an industrial or domestic supply.

MIG Wire

Mig wire is something people fail to consider with welding plants in this class, it is also a subject people need to understand when selecting a MIG welder as using the correct size mig wire is crucial to welder performance. In this area we have a choice of three sizes of steel mig wire which are 0.6mm diameter, 0.8mm diameter mig wire, and 1mm diameter mig wire and we need to understand the crucial role this plays in the performance of a MIG welder, and how it adversely affects a machines performance.

Wire size affects the limits of a MIG welder by its CSA or cross sectional area, this is the area the cut end of the wire gives us as the smaller the CSA the lower the maximum power it is capable of handling before performance drops off due to power overloading the mig wire. If we work out the CSA of 0.6mm mig wire it has a CSA of 1.88mm, 0.8mm mig wire has a CSA of 2.5mm, and 1mm diameter mig wire has CSA of 3.14mm diameter.

In general terms the most power 0.6mm wire can handle is 90 amps, 0.8mm wire can handle up to 160 amps, and 1mm wire can handle 300 amps, so why is this significant? Many cheaper machines claiming to be 250 amp machines only come set up for 0.6 and 0.8mm mig wire. They are often limited by only coming with drive rollers for 0.6 and 0.8 mig wire and the umbilical liner is only suitably sized to handle 0.6 and 0.8mm mig wire and not 1mm mig wire which means that your new MIG set cannot realistically use the last 90 amps over the 160 amps the largest 0.8mm mig wire can handle.

On a transformer based MIG set this isn’t so crucial due to its limited power pulses or frequency but on an inverter MIG it becomes more crucial due to its higher working frequencies meaning more power pulses are travelling down the MIG wire and it simply cannot handle them. Some manufacturers and retailers also use this to “sell up” which is to sell you a welder which cannot do the job it was designed to do unless you buy additional equipment from them at inflated prices, would you be happy buying a welder and then having to spend more to get it to do the job?

Imagine the scenario: you buy a cheaper MIG or dual purpose welder and it will only accept 0.6 and 0.8mm mig wire and the salesmen says “that will be another thirty quid for a liner, another twenty quid for a 1mm drive roller and another tenner for a pack of 1mm contact tips sir” would you be happy? In reality you would be better off buying a smaller MIG or combination welding set and saving yourself more money and having the machine which would do the job without having forced you to buy extra items just to get it to do the job its supposed to be capable of doing. To me its like buying a new car and it coming without any wheels and tyres.

Which size of wire spool can it take? Standard sizes of mig wire spools are 0.7Kg, 5Kg, and 15Kg and the 15Kg spool is the standard industrial size spool of mig wire, but the 5Kg spool has the same size centre hole diameter in the spool while the 0.7mm spool has a much smaller hole. Many MIG machines claim to be able to take 0.7 and 5Kg spools and if they claim this they have to come with a set of plastic adapters to fit inside the centre hole of the 5Kg spool to allow it to fit on the spool idler shaft which isn’t good as a smaller diameter shaft is weak and a future source of trouble. If your machine takes 5 and 15Kg spools of mig wire it comes with the much larger and heavier duty centre shaft to fit your spools.

If we look to costs we see a 0.7Kg spool of mig wire costs around £7 which equates to £10 per Kg of mig wire; 5Kg spools cost around £20 which equates to £4 per Kg of mig wire, and 15Kg spools cost around £30 which equates to £2 per Kg of mig wire. 0.7Kg spools of mig wire come in both 0.6 and 0.8mm diameters but try getting a 0.7Kg spool of 1mm diameter mig wire, you can’t. Spool size is dictated by the size of the MIG welder casing and if a 15Kg spool will fit then so will the smaller 5Kg spool as this is a smaller diameter spool, if most of your MIG welding is below 160 amps then go for the 15Kg spool of 0.8mm mig wire and a 5Kg spool of 1mm mig wire, it saves you money. If you are a periodic welder then go for 5Kg spools of 0.8mm and 1mm diameter mig wire because mig wire standing for any long periods means its copper coating protecting the wire erodes and allows the steel wire to rust and once rusty its scrap, you can’t spray this with oil to protect it.

TIG Welding

TIG welding is a totally different beast to MIG and stick welding and much more complex in many ways than traditional stick welding or MIG welding. TIG could be best described as the modern form of gas welding but on steroids as its so versatile and the TIG torch is a compact unit which allows very intricate welding of very intricate shapes.

Basic TIG sets come as a DC unit and it can weld mild steels, stainless steels, copper, and almost any metals except aluminium and aluminium alloys. More complex AC/DC TIG sets are required to weld aluminium and aluminium alloys as you weld aluminium and aluminium alloys with AC.

Basic TIG operation is similar to the old gas welding in principle as you feed a filler rod into the weld by hand and you generate the heat by using either AC or DC current which is fed through a handset or torch containing a pointed tungsten which directs the arc it generates very finely and accurately. TIG uses a gas shield in exactly the same way as MIG welding does and it uses a pure gas instead of a mixture of gases and this is argon gas as argon cleans as well as providing the gas shield and the shroud is made from ceramic with a much smaller hole than used for MIG welding and takes much more practice to perfect.

TIG tungsten’s come in a range of different diameters and different types depending upon the thickness and type of material you are welding and for our purposes they will be confined to the 1 – 3.2mm thickness range, basically the thicker the tungsten the more current it can handle. Tungsten’s are held in the TIG torch by a collet which is tightened by hand and you need a matching collet for the individual size of tungsten you use, and often a smaller shroud or ceramic as it is often called to match the diameter of tungsten to save shielding gas.

If we look at the front of a very basic DC TIG welder we will see a large array of knobs and it is this which confuses the beginner, firstly we have the base current control which sets the welding current as with any other welding machine. Next we have a switch which allows the TIG welder to switch between TIG and traditional arc welding so we select TIG mode for TIG welding and arc for stick welding.

Welding - John Bowden of Gumtree 4x4 Ltd.2
PHOTO: John Bowden of Gumtree 4×4 Ltd.

Pulse Frequency changes the frequency of the welder from our incoming 50Hz to a variable high frequency usually between 500Hz (0.5Khz) to 25,000Hz (25Khz) which means instead of 50 long pulses per minute we get a high frequency, or lots of very rapid short pulses depending on setting. These very rapid pulses are of a fixed rate of the base current setting and it is these high frequencies which give us the control and precision a TIG welder gives us when welding, and they are all set at the current we set and superior control of the heat pool which is the molten bit of metal.

Post Flow is the time we set which is usually between 0 – 10 seconds for the shielding gas to continue flowing after we finish welding, it works by keeping the TIG torch in the welding position after welding and the post flow gas cools and shields the weld and the tungsten in the torch to prolong its life.

Slope Up is the time it takes the machine to come from 0 amps to the amperage set to weld and is very useful, in simple terms if we set slope up to 5 seconds and the base current to 100 amps when the trigger is pushed it takes 5 seconds to come from 0 amps to its working power of 100 amps. This is a very useful feature when welding thin sheet materials as it prevents the edges of the thin sheet to be welded and not burned away as they would be using full power for a full and clean weld.

Slope Down is the exact opposite, just before you finish welding you release the trigger and the power winds down from its 100 amps to 0 amps over the time set, again it prevents the edges of thin materials being burned away at the end of the weld as it would using full power.

2T/4T is a function of the trigger and will be covered later.

If we look at the front of the machine it will have a positive and negative connection for the welding leads and two other functions:

Gas Connector – this connects the umbilical to the inverter and can be either a quick connector or a screwed connector and unlike a MIG set where it is built into the Euro Connector it has been accepted as standard on TIG.

Foot Pedal – This is to allow a foot pedal to be connected and you use this instead of the trigger on the TIG torch. On many TIG welders the foot pedal allows you to control the power like a car accelerator pedal, the harder you push it the more power you get. For advanced TIG welding on precision work such as uneven thicknesses of sections it allows you to crank the power up or down while you are actually welding, on some machines it may prevent certain functions from working such as slope up/slope down functions.

Tungsten’s used to be pure tungsten but now modifications have been made to them to allow them to work much better but different types only work on specific modes of TIG welder operation, pure tungsten is still available but rarely used these days as modified tungsten’s are much better. Zirconiated tungsten’s are designed to work on DC mode to weld steels, stainless steels, copper, and brass as we use DC to weld these materials and are marked with a white mark. Thoriated tungsten’s are used for aluminium and aluminium alloys and are marked with a red mark.

 ELECTRODE RATINGS  Maximum Amperage  Maximum Amperage Maximum Amperage
Electrode Diameter (mm) 2% Thoriated on DC (amps) Pure Tungsten on DC (amps) Zirconiated Tungsten on AC (amps)
1.0 80 30 60
1.6 150 80 120
2.4 250 130 180
3.2 400 180 250

As we can see from the above chart we have the maximum current which can be used for each size and type of tungsten.

One other type of tungsten is available and this is the ceriated tungsten which can be used as an all-round tungsten on all materials, basically you can use it on AC and DC and on all types of metals and even aluminium alloys. For general all round welding it may suit a beginner. Once you become more experienced you will find using the correct tungsten for DC or AC gives much better control, ceriated tungsten’s allow around 25% more current to be used without detrimental results.

Tungsten’s need grinding to a point and this needs doing properly, never radially grind any tungsten as this always causes the arc to waver and become unstable. Radially grinding is where you hold the tungsten at 90˚ to the grinding stone and rotate the tungsten against the grinding stone. Thoriated and zirconiated tungsten’s are ground to a point and then the sharp point is then ground off to leave a tiny flat end and this tiny flat end to the point ensures a stable arc, on ceriated tungsten’s you can grind it to a sharp point.

If we look at the R Tech 160 amp DC TIG it is a compact unit with 160 amps output on TIG and 125 amps DC in arc mode which makes it an ideal machine for a novice working on vehicle work, it will weld anything related to a car in TIG mode, and up to 3.2mm electrodes in arc mode. It isn’t over complicated to set up and you have a true dual function machine which will run at full capacity from a standard domestic socket, and for around £400 delivered at the time of writing. At this price you cannot go wrong; with a small industrial bottle of argon shielding gas you can put it in the boot of the smallest car and use it anywhere, the only downside is you cannot weld aluminium or its alloys so unless you work on something such as Land Rover alloy bodies its fine.

This machine has the benefit of pulse welding and slope up/slope down which many other similar TIG welders don’t and an industrial rating.

Many people make a classic mistake when connecting a TIG welder cables, for TIG welding you put the earth lead in the + positive and the TIG torch in the – negative connections on the front of the machine, for arc welding mode you swap the earth lead to – negative and put the electrode holder in the + positive connector.

More advanced TIG welders come with more features and a wide array of switches and knobs which will confuse any beginner so are best left to proficient TIG welders; nevertheless we shall look at, and explain the functions.

Peak Pulse – this is where you can set the pulsing action of the machine, leave it at 0 and pulse will be off, you set the pulse higher than base current and it pulses between the two currents. If you set your base current at 100 amps and peak pulse at 120 amps the machine will pulse between 100 and 120 amps.

Pulse Width – this alters the length of the pulse and most are between 0.1 – 1.0 seconds and you generally use this in conjunction with Peak Pulse to get precision welds on critical components.

AC/DC selector switch – this switches the machine between AC and DC modes and often requires the welder to be switched off before switching.

AC Squarewave Frequency Adjuster – often called “squarewave” and allows you to adjust the frequency from 20 to 250Hz as the higher the frequency the narrower the welding arc is, the lower the frequency the wider the welding arc is allowing faster travel speeds. Ideal welding squarewave is around 100 – 120Hz in AC mode and is considered the sweet spot.

AC Squarewave Balance (SP%) – this is the balance between cleaning ability and welding penetration and generally ranges from 30 – 70% and 50% is considered the ideal balance between weld penetration and cleaning. In simple terms if you have perfectly clean metal you would set it at less than 50% to get more weld penetration, on contaminated metal you would wind it up above 50% to get more cleaning.

2/4 way trigger – this often confuses people and its operation is simple, if the minimum power setting as 20 amps (called zero amps normally) then this is the welding current it will begin welding at and strike an arc.

2T – in 2T mode you pull the trigger and the machine goes through its slope up setting, i.e. from 0 (20 amps) to its base current setting over the slope up time you have set, you keep the trigger pressed and do the whole weld and release the trigger just before the end of the weld. When you release the trigger the power reduces from its base current to 0 (20 amps) over the time set for slope down.

If you leave slope up or slope down option at 0 it goes straight to full power set by the base current setting and stops as soon as you release the trigger.

4T – In 4T mode this works differently, you pull the trigger and hold it (position 1) and it arcs up at 0 (20 amps) and it maintains this 0 current (20 amps) and maintains this minimum power arc while you hold the trigger, this is beneficial to accurately align your arc. You release the trigger and it goes through the slope up time (position 2) and power comes up from 0 (20 amps) to the base current you have set and continues welding with the trigger released; as you near the end of the weld you pull the trigger and hold it (position 3) and it goes into slope down. Once it gets down to 0 power you release the trigger (position 4) and the machine stops welding.

If you have a foot pedal you can control everything from this, while it is good for bench welding a foot pedal is no good for automotive or site work as you need to be sitting to operate it. Foot pedal operation cancels the slope up and slope down times as you control the welding power using the foot pedal so you can just touch it for 0 (20 amps) power and push it gently to increase welding power while welding and release it slowly to decrease power while welding. As you can control power from the foot pedal there is no need for slope up or slope down; it won’t affect post flow.

Digital TIG sets are available and with a digital TIG set you get a screen and all of the buttons on the front of the machine are removed, you select a function and set it using a touch pad for supreme accuracy, once set it stores the setting in the machines memory. Digital sets do allow more functions and these are generally:

Memory Function – this is the ability to set and fine tune the TIG set for a specific job undertaken regularly and save those settings, when you return to doing the same job again you enter the memory and just select those settings and the machine sets them automatically. Most machines have up to 9 memory settings, some more, some less.

Multiple AC Waveforms – normal waveforms in AC mode are square in shape, hence squarewave, you can get soft squarewave, delta wave which are triangular, and sine wave which are semi-circular in shape and are for specialised welding far above anything we would be doing at home.

Power Factor Correction – this is the automatic correction of power to load ratio and the machine automatically corrects this factor depending upon the load placed on the machine and is a measure to save or reduce the mains power used by the machine when welding, or off load.

Microstart HF – often called high frequency starting ensures a better start, particularly on contaminated or dirty material and works in conjunction with SP% balance so the TIG set strikes an arc on contaminated material and the SP% balance it set to maximum cleaning and takes over the cleaning of the material during welding.

VRD – voltage reduction is something used by dual or multi-purpose machines when they are in arc welding mode, when in arc welding mode the electrode holder is always live when the machine is switched on unlike TIG or MIG modes which require the trigger to be pressed to power the welding torch. Arc welding has something called OCV or open circuit voltage and is the voltage at the electrode holder when not welding; with VRD this OCV is reduced to prevent electric shocks such as someone touching the end of the electrode or by putting a damp electrode into the electrode holder.

Cleanliness in TIG welding is crucial as it won’t deal with dirty metal and by dirty metal we mean even the oils which naturally occur in our skin can contaminate the metal so cleaning is important.

For rusty metals, particularly aluminium and aluminium alloys it is better to wire brush the area to be welded, for soft aluminium use a nylon brush, for steels a stainless steel bristle rotary wire brush on an angle grinder is preferred, this removes any loose contamination. Then switch to a nylon or Scotchbrite type pad on a Velcro backing pad on an angle grinder for aluminium and its alloys, for steels use a backing pad and resin bonded disc. Follow this up by wiping the area with a fine lint free cloth followed by a wipe with a cloth with cellulose thinners or similar; the lint free cloth removes the fine dust from grinding and the cellulose impregnated cloth removes oils, leave plenty of time for it to evaporate before welding.

Welding - John Bowden of Gumtree 4x4 Ltd.1
Sureweld MIG welder in action. PHOTO: John Bowden of Gumtree 4×4 Ltd.

Selecting a welding plant

This can be a daunting prospect for a beginner or relative novice, gone are the days when you had a choice of arc welding plants and what output they were as welding has moved on and so have the scams designed to get you to part with your hard earned cash for an inferior or cheap product. Is it mainly fabrication of 1.5 – 2mm thickness and above? Then you have the option of arc or MIG or a combination machine of arc and MIG.


Is your work mainly thin sheet metals or automotive type work? Then the advantage of TIG is obvious.

Do you weld mainly thicker materials including some aluminium and its alloys? Then a MIG with a separate umbilical with the Teflon coated liner is the preferred option, or just buy a separate Teflon liner if you don’t mind changing it every time you weld aluminium, along with the correct drive roller and tips.

Power input is crucial to a machines performance and many people buy a high powered, or poor performing machine and drop a standard UK three pin plug on and wonder why it doesn’t work, trips the power out, or in some cases burns their garage/workshop wiring out. This is because people don’t look at the machine specifications prior to purchase or the manufacturer doesn’t provide them on their website and people assume they can just run them off a standard UK three pin plug; in reality this couldn’t be further from the truth.

If the manufacturer doesn’t supply the input fuse rating on a website then E-mail them and ask them for this information; or if you use R Tech they put a full set of specifications for every machine on their site, and you can actually download the user manual from their site to get this information.

If we refer to the R Tech site for my Pro 250 dual purpose machine or the user manual which comes with the machine it clearly states the input fuse rating is 22 amps and it gives us a generator rating if it is to run from a generator of 7 KVA. UK standard plugs are rated at 13 amps as are their fuses and already we can see that winding up the power on a larger welding set will blow this fuse, and we already know the 13 amp rating is well below that 22 amp fuse rating of the machine and will damage the plug if we bridge the fuse with 30 amp fuse wire. This only leaves us with one option, industrial plugs; the same industrial plugs we see normally on 110 volt power tools, they also come in 240 volt ratings and are blue and not yellow as blue indicates 240 volt, and they come in two ratings, 16 and 32 amp rated. We can see 16 amp ratings are well below the 22 amp rated fuse our machine requires leaving us with only one choice which is the 32 amp rated plug.

If you have a garage or workshop supplied from your house chances are it will be wired on a ring main which will supply 30 amps total, if it is from a single cable from the house chances are it will use 2.5mm cable and this can handle a maximum of 25 amps, now we can see the problem. Having ring mains capable of handling 30 amps and a single supply cable capable of handling 25 amps feeding the ring main. You may well have installed the correct 32 amp sockets in your garage/workshop and this single 25 amp rated cable may be capable of running your high powered welder but add in a 110 volt transformer switched on, lights switched on, and any other powered equipment switched on and you soon exceed the 25 amp rating of your supply cable and your machine shows a fault from under supply.

If you have such issues or old wiring then the only option is to have it inspected by a qualified electrician and replaced with larger 4mm cable which will handle the loading from most garages/workshops, or even better have it replaced with 6mm cable and you will have no issues.

Generators have been touched on and my 250 amp set requires a 7KVA input and while similar powered welders require much larger KVA inputs it states “WITH AVR” and it is critical to understand this and what it entails. AVR stands for “auto voltage regulation” and this relates to the regulation of the generators output voltage and for good reason, some time ago I tested a number of cheap generators and their 12 volt output for battery charging and found they provided anything but 12 volts and many exceeded 20 volts which would kill a battery at such voltages. While we were testing the 12 volt battery charging output we tested the 240 volt output and found many exceeded 300 volts output; inverter welders and transformer welders won’t cope with such input voltages and inverter welders are more crucial on their input voltage. If you do intend running an inverter welder then only use a generator with AVR as this will control its output voltage and the extra cost of having a decent generator with AVR is much less than the cost of having to replace a welder, even if they are competitively priced.

If you don’t want the expense and work of uprating a garage/workshop supply it leaves you with the option of buying a machine which runs off a domestic supply.

Trust this helps!





















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Tom McGuigan