tack welding vs full bead

[kamaroman68]

Alright guys I have another question for you. Going to be mig welding thick metal to a thinner metal roughly 1/8 to 1/16. The 1/8" material being 304 ss and the 1/16th being plain old steel. I know you need to use the higher setting on the welder for the 1/8 ss. I am worried about burning through the 1/16th steel while trying to run a full bead. This is what I would call a structual part ( basically I am modifying a 68 camaro rocker panel). Could I just make a series of tack welds and go back and forth until all of the tacks are connected. Or would it be better to tack in place and run small beads roughly 1/2" to 1" long again with the chance of burn through. Thanks guys.

Chris

[parsonsj]

I would tack it firmly in place, down to tacks every inch or so. Then I'd stitch weld from there. Stitch welding is like tack welding, but you go much faster laying one tack on top of the previous. The timing is like 2 seconds on, 1 off. If the thinner material starts to fall through, increase the time the welder is off to let it cool slightly.

The other thing to do is to start the weld puddle in the thicker material and push it into the thinner material. That will help with fall through too.

jp

[kamaroman68]

I gotta say the people on this site kick ass and I mean that in a good way. I must of posted that question at 7a.m. est and already have an answer. Thanks everyone for the help. Much appreciated. Chris

[Matt@RFR]

For structural stuff, keep in mind that starts and stops are the places an otherwise good weld is allways predicted to fail. Minimize the amount of tacks you use, and run as long a bead as you can get away with.

Or you can tack the hell out of it and grind the tacks out, then run right over the tacks. Either way, minimize the amount of starts/stops.

A good thick to thin weld will have the bead offset towards the thicker piece, but needs to be no bigger than the thickness of the thin piece.

[roverhybrids]

no comment on welding SS to mild steel? I THOUGHT that this is a no-no?

[Matt@RFR]

Do a search. Chris asked the question before he got this far.

[parsonsj]

SS to mild steel

No, not a no-no. Care has to be taken to avoid ruining the anti-oxidation features of the SS near the weld, and the weld itself will definitely oxidize if left bare. But structurally, welding SS to mild steel will work fine.

Matt can tell us the right wire to use (by alloy), etc. Me, I'd use tri-mix and ss wire to give the best possible oxidation resistance at and near the weld.

jp