Keep blowing through

  1. JPN New Member

    Messages:
    12
    Location:
    Glasgow
    Hi all. Working on a BMW m3 and have some small repairs that need new metal welded in. Mostly around grommets that have rusted through.

    I ordered a Clarke mig 105en and some 1.2mm mild steel sheet from frost and started practicing to the point I was happy enough move to the car.

    Starting in the wheel well, I cut out the bad metal, cleaned up both sides around the cut to about 50mm from the edge and then used the 1.2mm sheet and created a repair piece, fitted well with only a couple small gaps. I tacked into place and everything was fine, was more than happy and then that's where it went Pete tong! Attempted to do the stitch weld process so as not to distort the panel and it just kept blowing holes, between both the new and old metal.

    At this point I changed wire from 0.8 to 0.6 and still the same, checked ground, still the same. Then I realised they had sent me a Clarke mig 106 en and the range was 40 to 100 amps so the lowest was too high! Sold it on as I had used it and got a Clarke mig Pro 90 instead.

    Started at it again yesterday, cleaned and grinded everything down, some is OK but lots of pin holes. Using 0.6mm wire, hobbyweld 5 and lowest setting it's still blowing through instantly. Even trying some folded copper pipe behind it but it's a mess.

    Any advice is appreciated. Thinking of cutting it out and starting again as maybe I didn't get enough of the bad metal out.
     
  2. Dcal

    Dcal Forum Supporter

    Messages:
    2,007
    Location:
    Antrim Northern Ireland
    Can you post a few photos?

    the 1.2mm sheet you are practicing on is probably a lot thicker than the steel on the car (like 50% thicker which is a lot.)
    What position is the patch?

    Practice on sheet the same thickness as the car and in the same position on the bench until you get the feel for it.
    A piece of scrap panel would be perfect.

    Really low settings might not help.
    By the time the steel has melted the weld is a mess.

    I find it better to go in hot and fast and let it cool between tacks.
    Concentrate the heat on the tack and then bring the weld with you but only in very short bursts.
     
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  3. JPN New Member

    Messages:
    12
    Location:
    Glasgow
    I'm away from it just now but will get photos shortly.

    The patch is in the centre of the boot floor, but as the car is on axle stands it's a good height so I can lean into the boot and against my weight against the boot opening.

    I actually ended up using the guidance in the manual and for 0.8 to 1.0mm thick metal it said use min 2 so I did and managed to plug the blow throughs. Looks OK when looking down but from under the car there are still pinholes.

    I seem to keep having to weld and grind and each time find pinholes and make more holes trying to fill them, or did on min 1 anyway. Hopefully after going hotter I'll have better success.

    I also seem to end up with a glowing blob on the end of the wire. What's causing this? Wire speed too low? Hard for me to tell when only doing tacks.

    Cheers @Dcal
     
  4. Dcal

    Dcal Forum Supporter

    Messages:
    2,007
    Location:
    Antrim Northern Ireland
    See if the blob disappears after turning the welder up a bit

    Believe it or not if you can get access (and I'm not suggesting you do this yet) it can be easier to weld from the underside because gravity works with you not against.
    If you are welding from above and at low power by the time its melted and you have a pool there can be a lot of heat and weld metal and it can fall through in a blob.

    As you’ve discovered if you weld from the top, when the top looks right the bottom can be a mess.
    If you weld from below, when the bottom looks right the top is usually pretty good as well.

    When you are starting the tacks don't put the weld on the cut edges.
    Get the weld going on one side of the joint and bring it over to the joint.
    If needs be, weld both sides and then fill the gap.
    When you have good tacks made you can work from the tack and bring the weld with you.

    For practice try welding the edge of some 0.8mm steel to see how difficult it is to control compared to a seam on solid sheet of the same size.

    Don’t worry too much about pin holes, they are very common on thin sheet but don't wait until you have the welds dressed before you deal with them because you will probably have thinned the metal and so it's harder to fix.

    Instead put a strong light source below the floor and look from above and fill as much as you can see in the weld bead.
    As you dress the welds back more might (will) appear but fill them as they become apparent.
    If there is a lot of weld metal about you may need to turn the welder up to get good penetration.

    Welding thin metal is not easy at the start but with practice it will be.
     
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  5. JPN New Member

    Messages:
    12
    Location:
    Glasgow
    I tried filling some pinholes from under and it seemed to go OK, blew some holes too but that was on the lowest power setting so I'll try again knowing what I know now.

    Should I try 0.8mm wire instead of turning up the power to max 1?

    just bought some 0.8mm sheet so should get it Tuesday. Will try on that before going to the next repair on the car.

    Am I better using thinner metal as the repair piece or the 1.2mm stuff is OK?
     
  6. Dcal

    Dcal Forum Supporter

    Messages:
    2,007
    Location:
    Antrim Northern Ireland
    I prefer 0.8mm wire but many people prefer and get great results with 0.6.
    If you have both wire sizes try them and see what works for “you”.

    Don’t be afraid to mess with the settings when practicing with test pieces on the bench. When you get settings that works try it on the car. The settings in the manual are just to get you started and all welders are slightly different so you need to tweak for best results.

    If you are getting 0.8 sheet as well, practice welding 1.2 to 1.2 (good place to start) 1.2 to 0.8 and then 0.8 to 0.8.
    The more you practice the better your welds will be.
    When you crack 0.8 to 0.8 the others will seem easy.

    If you struggle with the test welds post a few photos on here there are lot of people on here who can and will help out.

    1.2mm sheet will make welding the patch in easier, the only reason not to is if you are trying to keep everything original. The 1.2 will help you get a better weld when starting out.
     
  7. JPN New Member

    Messages:
    12
    Location:
    Glasgow
    Thanks very much. Very helpful.

    I was quite happy with my 1.2mm practice on both 0.6 and 0.8mm wire. I was happy with the tack welds and happy stitch welding 2 squares together, but obviously usly they were fresh, clean and thicker than the existing cat metal as mentioned. As soon as I moved to the car it was like starting again.

    Will practice more with the 0.8mm sheet when it arrives and post results.
     
  8. Dcal

    Dcal Forum Supporter

    Messages:
    2,007
    Location:
    Antrim Northern Ireland
    Another thing that might really help is using a backing strip under the weld.
    Copper or aluminium strip make a great backing, a copper one can be made out of a flattened copper pipe.
    If you clamp it to, or prop it under the weld with a jack or even sticks, so it’s tight to the metal where the weld is, it will give support to the molten weld metal.
     
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  9. hermetic

    hermetic Member

    Messages:
    135
    Yorkshire UK
    Only thing I can add to the above, is preperation. cut out all the rust, dont leave any thin or pitted metal, remove all the paint and underseal back to bright clean metal, make your patch 1/8" to 1/4" larger than the hole, fit the thicker patch from underneath, and weld from the top, using split second tacks to hold the patch in place. start the arc on the thicker metal and aim to just catch the edge of the thinner car body. using a hammer and dolly, tap round the patch till all the edges are in contact, and continue to go tiny split second tacks till it is fixed. there is no need to weld all the way round the patch, it can be seam sealed from the underside and then undersealed over, and stone chipped on top. A tack every inch is sufficient. Remember you are doing one of the most difficult tasks in welding, ask most welders to fix a car, and they will leg it! I find it much easier to weld thin metal with my huge 3 phase welder, than with my clarke 160 single phase, because the arc is more stable on the three phase welders. Once you have got the basic idea right, the only way is practice! Also try to get yourself into a comfortable, stable position, hold the torch in one hand, and steady the torch with the other hand. Wear gloves!! use an automask, and experiment with different levels, remember you will not get a flash even at the lowest setting. go just dark enough to eliminate the glare. If you wear glasses, try glasses on and glasses off (I weld glasses off.) Make sure you have no glare entering the back of the helmet from overhead lighting that puts reflections on the inside of the welding glass. lighting the area of the weld directly can also help. Good luck!
    Phil
     
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  10. weldingnovice Member

    Messages:
    74
    Location:
    Northeast
    I find it helps if you lay the torch over towards the horizontal as this tends to lay the weld on to the metal, with the torch in a more vertical position the wire will punch straight through as the heat is more concentrated.
    As said above I find it easier to have the amps up and go in with a short blast as it tends to go molten and fuse quick then let it cool, didn't have much option to be honest as my welder is 250 amp.
    Not sure what amps it goes down to but works better for me to weld with .8 on sheet and don't use it on it's lowest settings
    mk6 transit so has needed the odd bit of welding here and there
     
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  11. outofthefire

    outofthefire Member

    Messages:
    2,263
    Leeds
    You'll do better on min 2, don't even think about trying to weld a bead, just loads of tacks. Start with a couple of tacks on each side then work round putting a tack next each tack and move on working round the piece. If you blow through once or twice leave the hole and move on (you've probably ground that spot thinner) if you're blowing through a lot do faster tacks. When you've done put a bit of copper or ally under the hole and fill the hole in.
     
    JPN likes this.
  12. Matchless

    Matchless Member

    Messages:
    1,052
    Location:
    Essex UK
    I have just mig welded a patch into the front of a 96 year old tinned steel motorcycle petrol tank, used 0.7mm Zintec, 0.8 wire and No2 power setting on my 180 amp welder, lots of tacks aimed at the new metal, finished up with petro patch epoxy, original steel was a LOT thinner than the patch, like fag paper...…. not pretty but should do the job, was at the top of the tank, condensation damage,
     
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  13. JPN New Member

    Messages:
    12
    Location:
    Glasgow
    Thanks everyone. I think I'm as far as I can go with this patch now. Need a a light grind and hopefully no more pinholes.

    I have used the copper and found that it needs to be almost flush against the edges of the hole to work well.

    I finished off using min 2 and a high wire speed to try and get the amps up. The tack welds to fill in the holes seems much better, wish I had started like that.

    Not wanting to grind a lot as I'll get more pinholes so hoping that a layer of porpatch and seam sealer will hide the welds!
     
  14. Dcal

    Dcal Forum Supporter

    Messages:
    2,007
    Location:
    Antrim Northern Ireland
    Porpatch?
    Had to google that and it seem very expensive for snake oil.

    Do a search on here for painting steel after welding (there are lots)
    I’d go for an epoxy primer brushed on and worked well in to fill any remaining pin holes, Jotun 87A is my preferred one for the underside.
    This will even out the surface a bit, then seam sealer (if required because it's part of a seam) then under-seal.
    If you have the Porpatch it should work as well but I've never used it so know nothing about it.

    Lots of options out there, if you want to be fussy use 3m 2 pack stone chip. Expensive but as close as you will get to OM finish.
    I'm too cheap to buy it and use Sikaguard 6440 because it stays rubbery. Many people prefer a hard finish but the car makers like rubbery so thats good enough for me.

    See a link to the undersealing of an Alfa 75 I’m doing up but there are many more on the subject.
    https://www.mig-welding.co.uk/forum...the-brink-hopefully.81348/page-8#post-1315328

    If you are not easily bored, you can read the whole thing and you can see my welding improve as the job progresses (I think) so I’m not letting on I’m anything other than a diyer with more kit than most.
     
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  15. JPN New Member

    Messages:
    12
    Location:
    Glasgow
    I have it already, got it from a buddy so going to give it a try.

    For the underside I'm squared away, I'm doing an underside restoration so the underside is already stripped and all rust treated. Just need to do the welding which will get porpatch'd as they're small repairs, then full underside will get primed, seam sealed where required (including weld patches), primed and then upol raptor tinted body colour to finish.

    I'll give it a read as always interested to see other people's work and the products they use and more importantly the results!
     
  16. JPN New Member

    Messages:
    12
    Location:
    Glasgow
    0.7-0.8mm steel sheet arrived. First butt weld with it in pics below front and rear.

    Using 0.6mm wire, hobbyweld 5 at 10l/min, Clarke pro90 min 1, wire speed 6.

    Quite happy with that, but of nil penetration towards the bottom, this is where I did the first overlap tack. Need to work on my overlaps and I could do with better lighting in my garage as I ended up going completely on top of another tack.
     
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