Arc welding in the real world

[GeorgeB]

I started to put my practice sessions to some use recently when I tried to patch up some rust holes on my car, in preparation for the MOT. I'm glad I practised and got a feel for what works and what doesn't, with test strips of metal on a work bench first, but I found the practicalities of actual work on a car to be far, far more difficult.

This is using an arc welder to repair thin body panels, remember. The good news is that I'm having reasonable success in joining metal without blowing holes. Difficulties faced include:

- pre-shaping my repair panels to fit curved bits of bodywork, like the relatively complex panel shape behind the front wheels. This seems like a pressed panel. How can you recreate part of that?

- then, having got something roughly the right shape, getting it aligned and ready to weld is even more difficult.

- next, on this vertical panel behind the front wheel, access is very resticted inside the wheel arch. My welding helmet has a hard job fitting! On the work bench I get by fine without an auto-darkening mask. On the car, I'm already thinking that one of these automatic masks might make life a lot easier.

- and I'm on the verge of seeing that a MIG welder probably is the best tool for such a job. I can get by with the arc welder, but I suspect a MIG welder would be quicker.

 

[DuncanM]

When you say a complex panel shape, what do you mean?
To get a single curve, you need a pipe of the right diameter and some angle iron to weld onto it. Then you can just stick your sheet through the gap and bend it.
To get a double curvature you have to engage in some metal bashing. You have a choice of trying to thin out the middle bit or thicken the edges. The easiest thing to do is bash the middle until you create creases in the edges, and then to flatten the creases into the metal so it's flatish again. It's not easy to do precisely.
Another way I guess would be to do it like you would in card/paper and cut slots that you then weld. That would be pretty tricky though.
Cheers
Duncan

 

[3Rs]

Mig welding in my view was invented for the grease monkey. (Car mech)
Its takes time to perfect the skills, of welding and it takes time and experience to sus out how to get into a welding position. If i where in your postion make a template of out of card board this way you wont be wasting your metal, and it might make it easer for your self.

This will also able you to form the shape, and with the amount of times your having to get under the wheel arch you will quicky sus out what would be the best place to sit/lie down.

If your having problems making the same shape out of steel and your following your template, then make up a jig, Like what Duncan has explaned, only make the pipe the same length of the steel which you want to use.

 

[jrmig]

Practical Classics Magazine has had a few good articles on panel beating and forming repair panels using shrinking and stretching methods. You may want to check out a few back issues, I think its in October to December issues.

John

 

[Wozzaaah]

- and I'm on the verge of seeing that a MIG welder probably is the best tool for such a job. I can get by with the arc welder, but I suspect a MIG welder would be quicker.

I know someone who could do you a good deal on a Clarke!

 

[GeorgeB]

Thanks for the helpful responses so far. It's just started snowing. February really isn't the best time of year to prepare for an MOT. If the car passes this one, I must get another MOT in July, so it should be July thereafter; a better time to work. The latest snow means I might not be able to get back out there tomorrow, and try out any of these ideas.

I did cut out a piece of paper and in 2D it was roughly the right shape. But I'd need paper mache or plaster to take an impression for the correct shape. The curves/bumps or whatever are effectively 3D. It's not a good job to start on. And this is with my preparedness to go for the easy-route with an overlaid patch because the car is a bit of an old banger. It would be even more difficult if I tried to cut out a patch and then replace it within a new patch, perfectly butted up.Yet I know that's what a lot of you do, so I'm impressed. I'd almost expect to need a laser cutter and computer aided guidance to get sufficent accuracy.

Even just laying a straight patch straight on to existing bodywork (lap joint?), how do you keep the new metal sufficuiently flush, prior to welding? I'm thinking of using self-tapping screws to hold it down. The screws can be removed and holes welded over, once I've tack-welded the joint.

 

[simon718]

- and I'm on the verge of seeing that a MIG welder probably is the best tool for such a job.

 

[Sparkey]

I know someone who could do you a good deal on a Clarke!

 

[GeorgeB]

I know someone who could do you a good deal on a Clarke!

I have a secondhand MIG welder already and it probably works but I haven't tried it out. I got my priorities wrong. I should have concentrated on the MIG welder, rather than playing around with my DIY spot welder.

 

[Sparkey]

I have a secondhand MIG welder already and it probably works but I haven't tried it out. I got my priorities wrong. I should have concentrated on the MIG welder, rather than playing around with my DIY spot welder.

HALLELUYA!!! he has finally seen the light....

 

[Wozzaaah]

Arc eye?

 

[Sparkey]

Arc eye?

Not sure....does that affect your brain too?

 

[weldequip]

I have a secondhand MIG welder already and it probably works but I haven't tried it out. I got my priorities wrong. I should have concentrated on the MIG welder, rather than playing around with my DIY spot welder.

What machine have you got George? It should be pretty straight forward to put into commission if it's not working.
weldequip

 

[malcolm]

Please be sensible lads & lasses.

George, whatever welder you chose there aren't many 3D parts on a car. I use thin cardboard to work out a shape and reproduce that in steel (which behaves in much the same way). For just about anything underneath that should be possible - post some photos of the repair if you disagree.

The advantage of a reasonable MIG is it can be used for positional work on thin stuff without workarounds (like making tacks close together and welding over them), and especially without all the bother of trying to make an arc welder work up hill.

But we're not debating that here - let's help George out in this thread.

 

[rtbcomp]

If you need fairly gentle bumps in your sheet you can put them with a rubber mallet, resting the sheet on a sandbag. Again practise on some scrap.

 

[gavuk]

Even just laying a straight patch straight on to existing bodywork (lap joint?), how do you keep the new metal sufficuiently flush, prior to welding? I'm thinking of using self-tapping screws to hold it down. The screws can be removed and holes welded over, once I've tack-welded the joint.

once you have made up a patch ,ensure the area is cleaned (no underseal rust or paint), hopefully patch is somewhere close to required shape,then tack ,check position ,push patch to meet body work,where it touches tack again,then dress where patch is not in contact ,between the tacks,with a hammer drift etc to match bodywork. i often use my wooden hammer handle to push patch into contact with body ,jacks ,levers can all be used ,Closer you can get the tacks together the less bashing needed,auto mask will make the process easier as tacks need to be at point of contact.....this is not easy to describe ,hopefully you get the idea ,definatley get the mig going much easier...........good luck Gav

 

[Benji]

If you havent used an auto mask before, it will be a revelation to you. Worth every penny I promise you.

 

[scarecrow]

Are cheap mig welders as good as the more expensive ones
sorry George I just can't believe you were trying to ark weld paper when you already have a mig

 

[migwig]

Hi George -

I recently got a very good book off Amazon - 'How to restore Classic Car Bodywork' by Martin Tahddeus which has got loads on making replacement panels and fitting them. I'm finding it invaluable on my MGB!. Only cost about £10 (the book that is - the MG is worth a lot less!).

 

[GeorgeB]

The advantage of a reasonable MIG is it can be used for positional work on thin stuff without workarounds (like making tacks close together and welding over them), and especially without all the bother of trying to make an arc welder work up hill.

Yes, it's the high level of tacks and then an over-weld which takes more time with the arc than I think it would with a MIG but I'm pleased that it can be made to work, at least. The limiting factor and main challenge is not that, though, it's the problem of supporting a vertical patch say 1" x 3" in a place with no obvious way of clamping it; hence my thought of using temporary screws. A google search brought up references to 'welding screws'. Is that what they're for by any chance? Another thought was to use steel rivets and then weld straight over them. I couldn't even get a good first tack, due to the difficulty of supporting the patch. I did a poor first tack and when I hammered the patch to get a better profile, like gavuk suggested (later), it fell off! Not a good start, although anything I can clamp has been fine.

Benji - I was very grateful to Snowcat for his loan of a sophisticated auto-mask at last month's weld-off. Yes, it was a revelation (the first and only time I've ever used one) but I was still happy with my manual mask + bright light in a test bench situation. Working on a car is different, though. The need to rig up a bright light and aim it at the work is one further problem which I could now do without!

weldequip - my MIG welder is a Sealey Supermig 150. I was told the wire feed doesn't work but I haven't yet checked it out. I noticed that the fuse on the PCB has blown and I know that the motor works. I must set aside some time to try and get it working.

rtbcomp - I think these bumps could only be matched by hammering the patch over the top. The 'profile' is a bit irregular and I think it would be difficult to 'guess' on a workbench.