[Jet boater]

Howdy gents
I've searched quite a bit on the net to find some info on inverted MIG on Aluminum without much success.
I need to do some work in the bottom of my boat hull, and it would be much easier to not have to pull the motor and turn it upside down. I've welded for years but am certainly not a journeyman, but can produce good quality Al welds with both MIG and TIG, but I've never had to weld in the inverted position. Any advice you folks could give on this would be much appreciated. I can only imagine that trying to freeze the puddle fast enought to keep it from falling out will be the biggest issue. If I have to flip it for best results, well so be it. But if there is any way you can get good results inverted, that's what I would prefer. Will be using my Millermatic 251 with 30a spool gun.
Cheers

[AKweldshop]

Get some scrap and start practicing....

That's my best advice at the moment.

[AndersK]

Cant give any advice than to be extra careful.
The surface tension of alu oxide is quite high. So when overheating too much a larger amount can suddenly drop on you.

When it drops into your sleeve it will hurt a little until it burns through the fabric and falls on your shoes. When laces have been burnt of the metal will find its way through the holes down to your socks. A short while after, you'll be jumping around on one leg. After another short while when you mentally block the pain you start feeling hungry, smelling that fried bacon...

Welcome by the way

[Jet boater]

Man, it seems no one out there has ever had to weld in this position, and maybe for good reason.
Weld shop, thanks for the advice, but I can't imagine fabbing something up to practice on inverted. Guess I'll just pull the motor and flip it, no way I want to practise on the hull.
My boat is actually from just down the road from you in Wasilla. I'm over in the Yukon. You aren't on the Alaska Outdoor forum by chance are you?

[AndersK]

My main problem doing inverted alu mig was not using a spool gun. I had 2/3:d of a 10 lbs roll of wire lying on the floor wgen finished. The short moments when I got the wire running welding went well. Thats why I cant give any good advice other than what John said.
Take a sheet and try, then start dial in your settings until it runs.
No need to fab something fancy for the initial set-up.

[MinnesotaDave]

Heck, you didn't give any real information for people to go on. Thickness, weld type, hull damage, color of the boat, will people be watching you, riveted hull or welded hull, etc.

Absolutely best advice is to practice any weld you are unfamiliar with, in the position you need to weld it in, in the same conditions - then you'll know if you can or not.

Good luck on your repair

By the way, with a spool gun I'd flip it over too - with a tig I'd do it as an overhead weld.
(I'm not fond of spool guns - personal bias)

[soutthpaw]

TIG is really not that sensitive to the position. Place the pedal between your knees, assuming you are lying under the boat. Then use the pedal like a Thighmaster to control your amperage. Might experiment with pulse if your TIG machine has it

[gocirino]

I weld overhead MIG aluminum with pulse-on-pulse frequently and successfully. Does your Mig machine have pulse?

[Jet boater]

I weld overhead MIG aluminum with pulse-on-pulse frequently and successfully. Does your Mig machine have pulse?

I wish
Minnesota Dave, dude, what possible difference to the welding could hull damage have? Colour and will people be watching? Absolutely, there must be an ASME procedure for those.............
I have been mulling over TIGing it, for precisely the reasons you gents bring up. Not a lot of feet of weld, as I would be stitching it. Be a good excuse to get and on/off switch for the torch. I hate using a pedal in out of position welds.
Cheers gents

[noddybrian]

The hull color was probably a joke - but any paint or surface treatment will have an effect especially if the material is too thin to sand much - opinion on best solution does need all available info - sometimes you can picture the job in your mind but others joining the discussion can't visualize what you attempting & aluminum is always a crap shoot - so how big is this boat & what is the material thickness - if it's a little boat then the small amount of time to drain the motor oil / fuel etc is well worth it to avoid overhead - if it's like 30foot plus & needs a crane then sure go ahead & lay under it - consider steam cleaning prior to mechanical surface prep and / or heating with a torch to remove worst contamination - be sure to remove any bilge water or tilt away from weld area - if at all possible do not try to weld cracks on thin material without backer - always try to add a patch of new material plenty large enough to cover past ends of cracks & do not use square patches - put large radii on corners or make oval or tear drop ends - as to the actual welding - I would get some of the same material to practice & set the machine on then set it hot enough to create blow through / sagging on a continuous bead - running overhead usually needs slightly more WFS than down hand - now weld only an inch or two at a time -but pre-heat the initial start point - mig on aluminum always suffers from cold starts - then a short run of nice weld followed by overheating - short stitches done with plenty of power is the best way to avoid this from my limited experience - if your torch has wire speed trim control this helps - I once used a Cobra push - pull that had it as a thumb wheel in a place making truck bumpers & that welded quite nicely in any position - word of warning - at some stage a large blob of molten metal will drop so keep out of the way & wear adequate protection - good luck however you go about this - a picture would be great if you can.

[Jet boater]

I'd say the hull colour was definitely a joke, although performance anxiety is never a joke
It's a 3/16" hull, so lots of meat to work with. There definitely doesn't seem to be any "magic bullet" with respect to overhead MIG, at least as far as settings etc goes. Probably going to strip it out and flip it in my friend shop with his overhead crane.