Thin metal technique

[marlinspike]

Quick question. We have been practising with our Cebora Autostar using the thin metal technique and a copper plate as a heat sink. We were happy with our practise welds, both runs and butt welds, so started on the car. Not exactly a disaster, but what had come out as smooth, consistent welds on the practise metal now came out as more pigeon poopy, if you see what I mean. Also, blew through a few times - didn't do that at all when practising off the car.

The metal was thoroughly cleaned, seems to be about the same thickness, so not sure what the problem is. Had a practise session to get my eye in, but went pear shaped when it came to the real thing.

Power setting is 1 (lowest), wire speed is about 5 I think, gas flow was 8-10 I think. We are welding small square patches, say 3 or 4 inch squares, to fill rust holes in a door.

Any tips welcome. Thanks.

 

[Justme]

The car metal will be thinner than your practice metal from new & will have thinned some more due to rusting & your cleaning it up.

Keep practising. If possible get an old scrap panel to practice on.

 

[BrokenBiker]

car panels are usually around 0.8mm thick, not the easiest stuff to weld.

have you looked at the stitch welding tutorial on here? that's the only way I do it, never tried any other method on bodywork

 

[marlinspike]

It was the stitch technique we were trying to use. Looking at it today, I think you are right though guys, the car metal is very slightly thinner. As you say Justme, it probably thinned out a bit more as we de-rusted it too. I also think that we had too big a gap at the butted up joint. Tried to get a tight fit of the patch into the hole, but in places it just wasn't tight enough.

Frustrating though to be doing good practise welds and then, 2 minutes later, to be making a mess. Fortunately it is behind the bodykit so need not be neat.

 

[Dynamics]

Hi.

I too will be trying this soon. I would be interested to see some pictures of your results if you have any.

 

[marlinspike]

As the light was going, we dressed the welds down a bit and stuck some primer on to stop rusting, so you can't really see how poor they were. Several holes still to do, so I will post some pics of those if I get chance.

 

[BrokenBiker]

I tend to not leave any gap with body work, you don't have to worry about penetration, it will be there whether you want it or not on that thickness. just quick pulses on and off for about 2 inches then let that area cool, move on a few inches and start again. eventually work your way around the whole weld area until its all welded, dress back and then you can go over any pin holes.

be careful dressing the welds back though, it doesn't take much to go through

 

[Dynamics]

As the light was going, we dressed the welds down a bit and stuck some primer on to stop rusting, so you can't really see how poor they were. Several holes still to do, so I will post some pics of those if I get chance.

Cheers Mate.

 

[Dynamics]

I tend to not leave any gap with body work, you don't have to worry about penetration, it will be there whether you want it or not on that thickness. just quick pulses on and off for about 2 inches then let that area cool, move on a few inches and start again. eventually work your way around the whole weld area until its all welded, dress back and then you can go over any pin holes.

be careful dressing the welds back though, it doesn't take much to go through

Yes, sounds good.

It will be difficult for Me though, as it will be on a 4X4, so I don't want to use filler. The grinding/flapping work will have to leave the panel smooth enough to paint directly.

I will also have to learn to blend-in colour and clear coats to repaired area's

I have also got a floor hole to patch where the steel is corrugated!!!

 

[marlinspike]

There are some good threads on Retro Rides by tonybmw which show how to fabricate panels. Well worth a look if you have time - all pretty long.

 

[Dynamics]

There are some good threads on Retro Rides by tonybmw which show how to fabricate panels. Well worth a look if you have time - all pretty long.

Thanks for that, brilliant, only had a quick look through, but seem like great posts. He has lots of cool kit to use aswell.

I wonder how he goes about measuring and marking-out the steel.

True craftsman.

 

[BillJ]

I would echo Brokenbiker's comments about the gap. Any gap will make it much easier to blow through. I too try to make sure there is no gap but it is easier said than done and I seldom manage it. I have become quite adept at using the "TMT". I tend to use voltage setting 2 on my Parweld which I think allows me to use shorter tacks while still getting decent penetration.

Regarding thickness, depending on which panels you are welding the thickness on your 900 is likely to be nearer 1mm than 0.8, which makes these cars easier to weld (just as well...)
From doing a couple of driveshaft tunnel repairs, I know that the inner wings and driveshaft tunnels are about 1.2mm and the suspension tower nearer 2mm.

About dressing down the welds, again I concur with the opinion above. I managed to grind a tiny hole in the inner wing of my other half's 900 while dressing the weld with a flap-disk

De-rusted metal can be deceptively thin. I prefer to cut out a bigger piece if I can but sometimes that would make the job awkward.

 

[PaulMcElhinney]

Magnetic copper backer.

Frost Restoration sell a magnetic copper backer. This is a small triangular magnet with a copper face. If you can get one of these behind your work you'll be far less likely to blow through. Good luck.

 

[marlinspike]

Thanks for the tips guys. We did have a copper sheet to use as a heat sink, but still blew through once or twice. Will be trying again tomorrow hopefully if the weather improves. Hopefully we will get a tight fit on the metal oatches this time. Probably won't bother dressing the welds this as they are behind the bodykit.

Thinking about what Bill J said, we have automatically used the '1' power setting, thinking that less power is better on thin metal. It could be that having such low power meant we were holding the torch on for fractionally too long. Maybe slightly higher power and shorter contact time is something to try.

Having read a couple of other threads, I am also going to turn down the visor on my helmet. It's set so dark you can't really see the weld pool well enough. It's hard enough with wearing specs already without welding in the dark.

Really need to crack on with the welding as the weather will be making it difficult to do anything car stuff outside soon. Wish we had a workshop, or a garage that wasn't full of bikes and rubbish.

 

[PaulMcElhinney]

Copper backer.

I should have written rectangular, the copper backer is rectangular.

 

[marlinspike]

I had a look at the Frost one, but to be honest £20 is more than I would want to pay. It is a lot thicker than the £4 thin bit of copper I bought, though.

I had considered buying some welding magnets too, but I have read mixed reviews in terms of them affecting the arc. Anyway, still raining here so no welding today either.

 

[mike 109444]

If your copper backer is not tight against the joint on BOTH sides then you will get blow through. If you use some 1/2" copper pipe beaten flat then it can be bent to shape to sit round any curving of the area.

 

[marlinspike]

I think that might have had a little to do with it. The copper sheet was flat but the door has a very slight curve in it.

Here is the panel making thread from Retro Rides for those who haven't seen it. Some very nice work both on fabrication and welding:

http://retrorides.proboards.com/thread/70135/panels

 

[Bede]

That thread's fantastic. Great link.