straight or weave ?

[zardoz]

I was at my new Level 2 City & guilds MIG night class last night (got my level one certificate in the post the other day) I was doing my normal weld, when the new assistant tutor came and had a look at what i was doing. He told me to keep my weld as straight as i could, and not weave in a 'C' or whatever. He did a weld to show me and it looked pretty good to me with proper penetration. I tried the same and both tutors seemed happy with it and passed it.
I forgot to ask last night, but would it be that the 'ribbed effect' is purely cosmetic for Cap welds, and not needed for single run welds etc. ?

 

[Hitch]

Sometimes, the weave is needed to widen the weld suitably without building up to much height.
Or to limit the penetration in non ideal circumstances.
Joining heavy walled box sections on the radius for example.

 

[zardoz]

Ah! to limit penetration. I never thought of that one.

 

[malcolm]

Main reason it's in the tutorial is a bit of weaving guarantees the arc acts against both sheets. Get it wrong going in a straight line and you'd just bond to one sheet.

Does allow a slower travel too, and the wider bead is handy for thin metal where a straight run would give a bead a couple of mm wide.