Mig welding thin sheet metal

[jpgrego]

I'm in the middle of fixing up an old motorcycle I got for my wife to learn to ride on. One corner of the tank has some pretty severe rust damage and I've decided there's no way to really patch all the tiny holes so I'd like to just cut out the whole section and replace with new steel. However it's very thin steel (even moreso thanks to the rust) and I'm worried I'll blow through it if I just start blasting away. Anyone got some pointers before I get started on this or is it even worth trying?

Thanks,
Patrick

[pl_silverado]

keep the metal cool. tack weld, dotn try to run a bead, just use tacks until you have it welded all around, but make sure the metal doesn't get hot in between or you will blow through. use the smallest dia. wire you can find. .023 for a mig with c25 shielding gas. its just gonna take some time, dont rush it. it is doable.

[jimvannoy]

When I weld thin/rusty metal I hold the tip at a steep angle and try to let the wire hit the edge of the metal and not straight down on the top. Use a low setting and take your time.

[5wndwcpe]

There is a MIG wire out called EasyGrind. It makes for a softer weld bead which will help you when grinding it down, especially on paper thin material. One note of caution though, be absolutely friggin' certain there are no fumes present in that tank. Best bet is to have it purged (boiled out) before doing any repairs on it. I believe this is the eigth commandment of welding.

"Thou shall not weld on an unpurged tank for the noise will be very loud and thy friends will console thy widow in ways generally unacceptable unto thee."

[jpgrego]

Alright, thanks for the tips... I'll give that a shot and see how it comes out. Appreciate the advice

Patrick

[mulepackin]

I'd keep the portions not being welded on wrapped in damp burlap or canvas. As stated keeping things cool is big.

[Vicegrip]

I would take the extra step to line the tank with liquid tank liner when you are done. MiG has a nasty habit of cold starts. One cold start can let gas slowly seep and ruin you paint work. A cold start weld can get past a air bubble test. Tank liner is easy to install. Plug all the holes but one, pour it in the unplugged hole and then plug, slosh it all around and pour it back out. In fact some tank liners work so well they will fill and seal daylight pinholes.

[TNToy]

Good advice so far. Especially about the tank liner.

Use .023" or 0.25" wire, C25, and GO SLOW!

Oh, and if you're using a cheap welder, or one with just a couple of voltage settings, go ahead and just buy another tank now. Proper machine setup is crucial.

Tack it every inch. Then tack halfway between those, then halfway between those. REALLY thin sheetmetal won't let you go very far in a continuous bead.

[Bigger Hammer]

"Thou shall not weld on an unpurged tank for the noise will be very loud and thy friends will console thy widow in ways generally unacceptable unto thee."

I have nothing useful to add to this thread but had to say that was the funniest thing I've heard/read today. thanks:spit:

[5wndwcpe]

I have nothing useful to add to this thread but had to say that was the funniest thing I've heard/read today. thanks:spit:

Don't mention it. :thumbup:

[roundvalley]

Before you hit the tank, get some similar gauge metal and practice. Helps get all your settings before you blow a hole in the tank.

[PoorOwner]

if doing the little tacks all around, how do you avoid little pin holes, the start of each tack is a little cold sometimes. although if no breaks are taken the wire and the piece, should be warm enough, grind it down and test for leaks I suppose.

oh and if you position the piece somewhat more vertically it's less likely to blow through because the puddle won't tend to fall down.

[5wndwcpe]

Heat setting and wire speed are going to determine the rate at which your tacks will either build up on the surface or blow through the paper thin metal. When I was welding the floor in my '33 Plymouth, I had much the same problem. What I did was lay down tack welds every inch or so at as cool a setting as I could get. Go back and stitch them together but don't obsess about it if you miss a few, the object is to keep the heat down and yes, it will look bad. Next, grind down the beads and start the process over filling in the pinholes, increasing the heat/wire speed as you go. Rinse, lather, repeat. The idea here is that as you add the tack welds, you're adding mass to the thin metal, allowing it to absorb more heat, which will in turn, give you better penetration.

[rustywrangler]

if doing the little tacks all around, how do you avoid little pin holes.


That is the main reason behind the tank liner stuff.

You can avoid pin holes by starting on the metal and tacking vertically over the gap.

[RichardNorman]

So how did it work out? Have you started?

I do a lot of thin sheet welding with MIG and all the advice you got was spot on! I think the best overall advice is to get some scrap sheet of the same gauge or thinner and practice practice practice.

Just remember, the grinder is your friend.

Also, if (when?) you blow through at some point, fight the urge to try and fill that hole up right away by piling in loads of wire!! Put the torch down and take a break!