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Weld Preparation

Monday, 24th August 2020
Graham (Tech Advisor)
The Welders Warehouse Online Shop

For most things in Life, preparation is important, Weld Preparation is no exception.

There are some fairly obvious weld preparations

  1. Make sure the metal to be welded is free from grease or paint.
  2. Make sure the metal to be welded is free from rust or other corrosion.
  3. Try to place your Work Return (Earth) Clamp on one of the pieces of metal to be welded, rather than another part that’s joined to the parts to be welded (doesn’t apply to Gas Welding).

Where thicker metals are to be welded, a joint preparation may be needed.

Butt Weld Preparation

Typically, this would involve creating a ‘V’ preparation by grinding a chamfer onto each piece of the joint.

Butt Weld Joint Preparation

A 60º Chamfer is ideal, but you don’t need to get over precise with it.

As a Guide, “s” should be around 2mm, or 1/3 of the metal thickness, whichever is the lesser.

As a Guide “g” should be around 0.5mm for metal up to around 2mm thick, then around 1/4 of the metal thickness for metal from 3-10mm thick.

Fillet Weld Preparation

Fillet Weld Joint Preparation

Fillet Weld Preparation is a little simpler. Here I would make sure the upright piece of metal has nice sharp corners where it meets the flat piece of metal.

The reason for this is it’s easier to get good penetration if the corner of the upright is nice and sharp. A radius on the corner will mean the arc will need to burn in deeper to create good root penetration.

Why Clean Metal is Important

Firstly, attaching your Work Return Clamp (Earth) to clean metal is important because you need a good electrical contact for Arc Welding processes (Mig, Tig, MMA).

Secondly, surface contaminants like Rust, Grease and Paint will vapourise under the extreme temperature of the welding process.

Vapourised contaminants can then bubble up through the weld and get trapped as the weld solidifies. This leaves bubbles trapped in the weld (a bit like Aero chocolate), weakening the finished weld.

Vapourised contaminants will also create nasty fumes that can be particularly hazardous if breathed in!


Weld Preparation is important, so shortcuts should be avoided.

Clean metal is important for both finished weld quality and your health!

I hope you found this blog article about Weld Preparation useful.

Please let me know what you thought by leaving a comment.  

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  1. Albert Sevilla says:

    I understand the purpose of weld prepping, and a Fillet weld not really needing a prep(chamfer), but is this acceptable with AWS?

    1. Graham says:

      Hi Albert
      A sharp corner, rather than a chamfer is better for Fillet Welds as a sharp edge will make it easier to get good penetration.
      Regards Graham

  2. Kevin Johnston says:

    I am a novice, hobby welder, this article is very helpful. Thank you very much.

    1. Graham says:

      Hi Kevin
      Your very welcome, glad you found the article useful.
      Happy New Year

  3. Temptation Mambondiani says:

    It’s a good article thank you soo much

    1. Graham says:

      Thank You for the positive comment, much appreciated, glad you found the article useful.
      Regards, Graham

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