Clarke Pro 90 Mig Welder Review – A beginners perspective

Thoughts on starting to weld with this popular unit touted as ideal for classic car restoration

Probably the most daunting aspect of embarking on a classic car restoration as an amateur is the bodywork. It is also one of the most expensive aspects to have done professionally. So you are left with a choice. Accept the cost and get someone else to do it, or get stuck in and learn to weld.

There are a range of alternative methods for welding (Stick, Mig, Tig, Arc etc.), which all essentially rely on imparting just the right amount of energy into the metal (joint and electrode) to melt and fuse it all effectively together. The most popular for classic car restoration, and reputedly a good choice for beginners, being Mig, or Metal Inert Gas. The gas component is about seperating the metal from the oxygen in the air which is essential for an effective weld.

How does Mig welding work?

The concept is pretty straightforward, as the trigger on the welding torch is depressed a wire electrode is fed into the weld pool, whilst imparting the right amount of electrical energy to fuse the metals being welded effectively together. Too little energy and the weld doesn’t fully penetrate the join, i.e. fuse fully together the metals. Too much energy, and especially when working with thin metals and you risk blowing right through the metal, i.e. burning holes. This is where light mig welders such as the Clarke Pro 90 reputedly come into their own. Offering low enough amperage for working with thin metals as a price tag to suit the DIY welder.

There are 4 key components to the Mig Welder: a power supply which provides the appropriate level of electricty for the weld; the wire feed system which supplies a continuous feed of the wire through the torch to the weld; the torch itself which is typically a gun style handle with trigger from which the wire emerges through a weld tip and shielding nozzle; and finally the gas supply which shields the weld from the surrounding atmosphere using typically CO2 or an Argon CO2 mix.

Clarke Pro 90 Specifications

Core specs and comments are as follows:

• Power: 25 – 90 Amps – there are 4 voltage settings to choose from.
• Wire size: 0.6 or 0.8mm – it comes with a spool of 0.6mm wire and 0.6mm tip installed (o.8mm tip supplied)
• Claims to weld up to 4mm (general feeling is that really this is only suitable for <3mm metal mostly)
• Input: 230V on 13amp. Will run off a conventional domestic power supply.
• Comes with all you need to get started: 1kg wire spool (0.6mm), small bottle Co2 welding gas (390g), regulator, terrible welding mask.

It’s a weighty little unit, and not on wheels but seems well made and robust. The side lifts easily off to reveal the wire feed, spool mechanism etc.

Tip. Bin the included hand held welding mask and buy an auto darkening mask. Beginning welding is daunting enough without trying to do things one handed in the dark.

Setting up the Pro 90

Once the wire is in place the gas is attached via the supplied regulator, which is a bit flimsy and lacks a gauge or fine tuning control, but works well enough to get started. The gas bottle is attached to the rear of the unit with a large jubilee clip. Simple but seems to work fine. I set the gas to pretty much the minimal consistent flow for my first tests, around 2- 2.5 on the supplied regulator although forum reviews suggest these regs are not the best so trial and error may be required.

First attempts at welding

I started by playing around with a standard sheet of 20 guage (0.9mm) mild steel. There is definitely a bit of a knack to getting the action right, but after a while I have been able to lay down a neat enough bead, for bodywork it will be ground back anyway, with what looks like good penetration. For those who are not familiar with the concept, I read that a good weld should be almost symmetrical, with as much new metal on the underside as the face of the weld. It is very possible to lay down a neat looking weld which is barely fused to the joint and therefore no real use.

Tip. Holding the electrode at a 50-60 deg angle to the workpiece with the nozzle touching seemed to work well for each weld dot.

The importance of heat management

Whilst it was fun to try welding a successful bead with the pro 90, and I achieved this very satisfactorily, the sheet was quick to warp. This is nothing to do with the welder and a good lesson in heat management.

Tip. Some people advocate laying a wet cloth on the metal to soak up excess heat but the biggest key seems patience.

Welding 101 dictates that when trying to weld thin sheet metal unless you take things super slowly it WILL warp. By super slowly that means joining the dots, i.e. welding one dot at a time. If you are welding a patch you also alternate your dots on different sides of the patch to spread the heat.

Control variables on the Pro 90

The control panel is a simple affair. There are two power switches (1/2 and min/max) and a wire feed speed control knob. For my experiment I found 1/Max with a wire speed of 5 seemed to work effectively for 20 guage with a 0.6mm wire. Penetration was very satisfactory, a gauged by a similar depth of metal either side of the finished weld. It is quite easy to weld a nice looking bead which actually fails to penetrate properly and is therefore weak.

The final control parameter is of course wire feed speed. My initial mis-conception what that this is purely about the speed at which you are welding but this is not the case. Once a voltage is selected the wire feed speed will control the length of the arc. The shorter the arc, the hotter it is.

Tip. Wire speed is not just about the speed of the welding process. It actually influences the amperage which determines the heat of the weld. If you are not getting penetration it might seem natural to up the power but wire feed speed, as well as angle of torch and distance from workpiece all affect the heat and therefore effectiveness of the weld.

So it’s all a bit of a balancing act. Getting the power selection, wire feed speed and even welding action right are all key to making an effective weld.

What else have I learnt so far using the Clarke Pro 90?

There are a few other tips I have picked up so far to help with getting good results from the unit:

• Preparation of the metal is key. If you try and weld greasy, rusty or painted metal you won’t achieve a good weld. I have found paint stripper disks on a grinder are a good way to get to a clean surface.
• Cleaning the area to weld before cutting out the rusty area to be patched is recommended. If you cut first you risk thinning the edges of the metal whilst cleaning which make it much easier to blow holds in the weld.
• Edges blow through more easily as there is less metal for the heat to escape to. A few ideas to minimise this are: to back the weld with a block of copper which can be knocked off easily afterwards, or weld a bigger piece of metal and cut back afterwards.
• Ensuring the return clamp is cleanly attached to bare metal is essential to prevent an inconsistent arc.

So would I recommend the Clarke Pro 90?

Based on my experience so far I am happy with the Clarke. It is a cheap unit but even as an unskilled beginner such as myself it’s clearly possible to achieve acceptable results. It doesn’t matter so much if the weld doesn’t look perfect if you are grinding it back anyway. It’s not a professional quality unit, there is no cooling fan and a short duty cycle which would presumably irritate pro’s, the packaged regulator is functional but that’s about it, and the mask is almost pointless to include. But all in all if you need a low power unit for classic car restoration at a modest price it’s hard to argue with it.