To leave a gap on 1mm sheet or not

[Harry_Worth]

Been away from my MIG for a few months - sadly due to a bereavement.
Thought I'd get started straight away on my car after much practice on bits of metal. Spent ages making my little repair section. Tacked it in place and cautiously butt welded it in. Maybe too cautious - Looked round the back and my penetration in places was poor and yet I'd also managed to blow holes where my patch wasn't quite touching. Cut the duff piece out and made another patch and welded this in - another hole blown but not as big. With the patch a perfect fit I have to wind up the amps to get penetration which means I'm always on the verge of blowing a hole if my patch isn't quite accurate enough. I can never cut a straight line so in real life i.e. working on my car I feel I'm always going to end up with a gap. I experimented on some scrap steel, dropping the amps right down but leaving a gap - Apart from my wire shooting through the gap all the time I did seem to have some success. There does seem to be potential to do it this way and I can then use my intergrips. More practice but I can't help feeling that even on thin stuff, leaving a gap is the way to go. Am I correct in going down this path or is this just another blind alley!!!!

 

[rtbcomp]

Try leaving a gap the same thickness as the wire, which in this case should be 0.6mm

Welcome to the Forum by the way!

 

[Drains]

In many circumstances a gap is entirely appropriate. Exceptions would be autogenous Tig and oxy/acet.

As you've worked out, you can use lower amps and get more control, but still get good pen, and stop burn-through. A bit more practice and skill in keeping the wire in the leading edge of the weld pool ( instead of in front of it) and you'll be sorted.

 

[Harry_Worth]

In many circumstances a gap is entirely appropriate. Exceptions would be autogenous Tig and oxy/acet.

As you've worked out, you can use lower amps and get more control, but still get good pen, and stop burn-through. A bit more practice and skill in keeping the wire in the leading edge of the weld pool ( instead of in front of it) and you'll be sorted.

Thanks Drains - back in the garage tomorrow to try out the theory! Think I'm getting there - slowly!

 

[Sphinx]

In my experience of thin metal, and I'll admit it's limited, I get the piece to fit as well as possible with little (a mm or less) or no gap and work that way. I find it much easier not to blow through but also get good penetration, if there's a gap I find it's very easy to blow holes unless you're very careful in using the previous weld to helb bridge the gap.

 

[michael1703]

this might sound odd, but i sometimes use paper

if you want a tight weld but want to leave a gap for good penetration and to allow for a bit of expansion i tear a strip of paper and put it between the two pieces

if you want a bigger gap you could cut an inch of mig wire and pinch it between the two pieces

 

[graann]

Mig V butt root gap

I wonder if anybody could help me.
After preparing a v butt weld on 5mm mild steel ( 60 degree included angle ) I have been leaving a root gap as big as the root face ( 2mm ).
One problem is that my 0.8 mm wire goes straight through the root gap, I obviously need to move side to side ?
Another problem is that I don,t always get full penetration and have been told to increase the root gap.
I am at college doing a welding course
I have been advised to do the v butt weld , firstly with a root run and then a cap.
I find that I usually fill the v in one run.
Can anybody give me any advice ?


Thanks
Graham