[Rick_H]

Gotcha....I'd preheat the lower piece, clamp it tight then weld it. I'm thinking the thinner piece is lifting slightly and since the thick material isn't got enough your just destroying he edges... I'd preheat and use a small diameter filler. 3/32" tungsten should be fine.

[bobthe]

by preheat, what do you mean - as in heat in an oven? if so what sort of temp should I be using?

Thanks!

[AKmud]

If the filler beads on either side, heat probably isn't the problem. It sounds like something is gassing out in those places and dividing the puddle. Maybe a bit of cleaner or oil is trapped?

[bobthe]

i dont see how it's a chance of something being trapped. the parts were thoroughly cleaned with acetone before welding

[Superiorwelding]

I am thinking the best help for us is more detailed pictures. Try to get at least 6 good pics. Get us before the weld, during the weld and after. Show us the problem spot both before, during and after. A bigger scope of the part will really be helpful. We really want to help if we can and don't want you to go away without your answer.
-Jonathan

[bobthe]

sadly that wont be possible. by the time i made this thread i had done all the welding I had to do, and on friday I sent the parts out for someone to fix my attempt at welding :/

[Rick_H]

Were the parts clamped down tight while welding?

['Stang]

How much of a point do you have on your tungsten?

Has the tungsten been sharpened 'axially' to the grinding wheel (the grinding lines follow along the length of the electrode, not across it)?

Can you increase frequency on the welder? That sometimes will help to focus the arc.

What size electrode? Too big can cause arc flutter.

Trevor

Sorry! You can't adjust the frequency on DC. That is a function for AC. Sharpen your tungsten to a point, and direct your arc where you want it. The pictures look like you are running too cold. And you need good gas coverage to weld stainless. If you don't have good gas coverage, the metal won't puddle right. Hope this helps.

[RichardH]

From the sketch you posted, it seems like there's a good opportunity for the thin piece to end up getting hot much faster. If the parts aren't clamped together, a hairline gap is enough to keep heat in the thin piece instead of it wicking into the thick piece. Since it's got less mass, it'll heat to melting first, bead up, and melt back from the joint.

Perhaps, is the problem area a spot where the thicker part gets significantly thicker? Or there's some change in the lap joint geometry (like more overlap)?

If you keep the arc in the puddle and work the puddle forward, you'll get heat transfer to both sides of the joint, but if the arc gets ahead of the puddle it'll wander to one side or the other and melt it back. This might happen if suddenly there was more metal in the area (thicker section, screw boss, etc.) that wicks away more heat and the puddle gets cold. Rather than attacking it like a restart, back up to the puddle add heat to get a good puddle going again, and work it forward with heat flowing into both parts.

[bobthe]

Sorry for the slow follow up.

I should have offered this detail in my drawing, but keep in mind that these parts are a small disc that nestles inside of a larger disc, so there is no way fort he edges to pull apart while welding. The smaller piece is clamped down to the bigger, so lift isnt an issue either.

when welding i saw no sign of the puddle pulling away from the edge at a problem spot, it was simply an issue of the bead stopping, as though there was a transition in the material (of both pieces) from stainless to unobtainium. I tried backing up and the material would puddle nicely in areas where there was already a good bead, and then when i got to a problem spot the bead simply stopped.

[TRACKRANGER]

How much of a point do you have on your tungsten?

Has the tungsten been sharpened 'axially' to the grinding wheel (the grinding lines follow along the length of the electrode, not across it)?

Can you increase frequency on the welder? That sometimes will help to focus the arc.

What size electrode? Too big can cause arc flutter.

Trevor

Sorry! You can't adjust the frequency on DC. That is a function for AC. Sharpen your tungsten to a point, and direct your arc where you want it. The pictures look like you are running too cold. And you need good gas coverage to weld stainless. If you don't have good gas coverage, the metal won't puddle right. Hope this helps.

My Bad
Had a big day on Aluminum that day, obviously I just couldn't let go

[GreinTime]

Don't worry, Jonathan thought he was using .040 tungsten and trying to weld at 110 amps

[TRACKRANGER]

Don't worry, Jonathan thought he was using .040 tungsten and trying to weld at 110 amps

Jonathan, I know exactly how you feel...

Better luck next time

[Bill Beauregard]

I don't do much stainless. Aluminum can misbehave when I get into an awkward position. Starting a bead can be tricky. I try to heat one side of the joint, then the other. Once hot enough,I can add a bit of filler to one side, and wash it to the other. Once the two pieces are bridged, I focus the arc on the leading edge of the advancing puddle, this seems to help the arc focus where I need it, and the fluid metal is great for conducting heat evenly. It is most helpful at evening out heat when two pieces are different thickness.
As for grind, I believe a blunt (golf score pencil) grind works better than a needle grind. The arc will start at the first irregularity in the surface. Is your stick out long enough? At least half your cup diameter works well. Is it possible you are experiencing arc blow, a magnetic influence on your arc caused by electrical current in the workpiece? Move your ground clamp, change the angle of your tungsten. More amperage, or smaller tungsten could help.

[Superiorwelding]

Don't worry, Jonathan thought he was using .040 tungsten and trying to weld at 110 amps

Jonathan, I know exactly how you feel...

Better luck next time

It happens to all of us
-Jonathan

[dsmabe]

If you have the opportunity to try these again I'd say put several tacks, then backstep your welds.