Leaving a gap in butt welds

[bluenose]

Hi,

I was reading this website and it said if your butt welding a thickness of less than 1.5mm you shouldn't leave a gap.

I want to do car body panel replacements so its thin metal and I'm just trying to think if you've got about a meter or so of panel to weld together how you'd keep it lined up without a gap and some clamps between the panels.

I was thinking about making some of these as a little project to practice on see;

http://www.eastwood.com/media/catal...ge/9df78eab33525d08d6e5fb8d27136e95/p354b.jpg

but i won't bother if its bad practice and there's another way.

 

[Chickenjohn]

That advice would only apply to gas or Tig welding if you want to weld without using any filler rod. When I am butt welding 1mm car panels, I do try and get the fit as good as I can. But as MIG welding has a continuous supply of filler wire when you pull the trigger, a 1mm or smaller gap seems to work, especially if you are doing the weave technique or pulsed welding. The small gap is OK, I think it ensures you get good penetration, just have to make sure your settings and technique are up to it, so you don't end up burning one side back.

Yes, I have used intergrips to hold the patch in place during welding and they work fine.

 

[outofthefire]

I wouldn't leave a gap, I find i'm more likely to blow holes with a gap, although thats probably more to do with my technique . I'd just tack every 3 or 4 inches keeping the joint tight.

 

[bluenose]

That advice would only apply to gas or Tig welding if you want to weld without using any filler rod. When I am butt welding 1mm car panels, I do try and get the fit as good as I can. But as MIG welding has a continuous supply of filler wire when you pull the trigger, a 1mm or smaller gap seems to work, especially if you are doing the weave technique or pulsed welding. The small gap is OK, I think it ensures you get good penetration, just have to make sure your settings and technique are up to it, so you don't end up burning one side back.

Yes, I have used intergrips to hold the patch in place during welding and they work fine.

It definitely says it in the mig welding section. Quote:

A root gap between two sheets will reduce the power needed to penetrate fully through the joint. This is the last thing you'd want with thin metal as the power setting on MIG welders doesn't go down all that far. Any steel up to 1.5mm is best welded without a gap, though a small gap or perhaps between 1/2 the thickness of the steel can be useful on steel thickness 2mm or above.

Its on this page;http://www.mig-welding.co.uk/butt-weld.htm

 

[malcolm]

That's only my opinion (I wrote the page) but the forum is open so you might also benefit from some different opinions and ideas on here.

Those clamps need a 1mm gap, but it can be 1mm ground away only where the clamp will sit. I don't use them myself. I prefer to line things up and tack weld.

To get the shape right crop the repair panel to just too big, then scribe along the edge either on the repair panel or on the existing panel and trim to shape. It should be possible to get things lining up quite accurately.

 

[bluenose]

That's only my opinion (I wrote the page) but the forum is open so you might also benefit from some different opinions and ideas on here.

Those clamps need a 1mm gap, but it can be 1mm ground away only where the clamp will sit. I don't use them myself. I prefer to line things up and tack weld.

To get the shape right crop the repair panel to just too big, then scribe along the edge either on the repair panel or on the existing panel and trim to shape. It should be possible to get things lining up quite accurately.

I like that idea of grinding out the sections where the clamps will go, best of both worlds. I think i will crack on with making some of these clamps, they look like they'd make welding the panel straight much easier for me as it will be my first go.

Thanks for the feedback!

Pages are very helpful by the way, nice one

 

[gavuk]

I'm sure the clamps can be useful ,if you are a new welder ,i would say your time would be better spent practising on scrap off the car ,trying butt welds ,and especially vertical.....can you tell us more of what your doing is it mot work or full resto?...1metre long ,,sill?...

 

[bluenose]

I'm sure the clamps can be useful ,if you are a new welder ,i would say your time would be better spent practising on scrap off the car ,trying butt welds ,and especially vertical.....can you tell us more of what your doing is it mot work or full resto?...1metre long ,,sill?...

got a bay window VW bus. All the structual welding has been done by a professional before i brought it but but on the body its had a lot of filler put in it and a blow over respray.

Its also had a bit of an accident down the passenger side so the main job i need to do first is replace the large rear side panel and reskin the sliding door.

I basically want to stick it in my garage in october, take the paint off, and replace any rusty bits.

So I need to get practicing and be half decent at welding by then!

Just finished restoring an MGB but got someone else to do the welding, really want to be able to do it myself in future resto's.

 

[outofthefire]

If you grind some of your metal away to fit clamps you'll have to fill the ground out section. If your new to welding and restoration you might want to try and get this dvd http://www.metalshapingzone.com/shop/catalog/browse?shop_param= although he uses a gas welder the principals are the same. There's also a really good video clip online somewhere of an American chap mig welding a panel, but I cant find the link, if I find it i'll post it later.

 

[bluenose]

If you grind some of your metal away to fit clamps you'll have to fill the ground out section. If your new to welding and restoration you might want to try and get this dvd http://www.metalshapingzone.com/shop/catalog/browse?shop_param= although he uses a gas welder the principals are the same. There's also a really good video clip online somewhere of an American chap mig welding a panel, but I cant find the link, if I find it i'll post it later.

by fill do you mean body filler? I was thinking it would only be a 1mm gap for the clamps so would just weld it together.

if you could find the link that would be good, been watching videos on youtube but haven't thought much of the ones i've found. Trying not to spend anymore cash at the moment because i've been spending all my £'s on the welding gear lol

 

[outofthefire]

The link below is from an american site on the second page there are some good pictures of the process. The trouble with filling the 1mm gap with weld is that you might cause the panel to distort because you'll be putting more heat into the gaps than you have over the rest of the join. It all depends on how close to being spot on you want it and how much filler you want to use.

http://metalmeet.org/forum/showthread.php?t=798&highlight=mig+welding+sheetmetal

 

[droopsnoot]

I've used intergrips as well. The problem I found is that after the weld, they can be a bi**h to get out because the gap has closed up due to heat. So to be sure they'll come out, you end up leaving a bigger gap, and so on. The good thing about them is they do clamp the two sheets level which can otherwise be a challenge.