More weld questions

Argeo · 12-13-2004, 07:10 AM

I was wondering what wire thickness people typically use for fixing holes in panels with a mig. I believe I am using .31 or .0031 or something like that. I thought someone earlier had said it is to thin and would make my life easier if I used a thicker wire. I notice problems when the piece I am putting in is a bit smaller than it should be. The space is very dificult to fill. I know it depends on the gap I am looking at but if the space was a 1/16 of an inch bigger than it should be, would a thicker wire make my life easier?

Next, I am putting a piece of sheet metal on the door sill where the sill curves from horizotal to flat (towards rear of car, typical rot spot I hear). Anyways, I am having a dificult time fitting my welder into the area where the rubber door seal would go because of the lip on the body. Any suggestions? Can I take the end of the nozzle off so the nozzle tip would be exposed? It is much smaller in diameter than the metal piece that protects it. Is there a reason it is even there other than to procect from welding the tip shut? I have done a number on the original metal surrounding the area I patched with the gun grounding on a good piece of metal while trying to weld this area. Thank god for bondo.

The piece is on there and ain't coming off because it is connected to three other sides, so strength is not a factor.

Oh, I don't think I will able to grind in there either?

Maybe do several spot welds instead of a nice bead? Any suggestions?

Thanks for your help,

David

Thanks,

cstreit · cstreit's Garage

I actually use .023 for welding panels, but my welder doesn't have infinite amperage adjustment. If I try and use .030 now, I burn a lot of holes.

.030 is fine if you can get enough amperage for penetration without burning holes through the edges.

RickM · RickM's Garage

Thicker wire will be harder to fill gaps on thin sheet. It takes more energy to melt it which will result in burn through.

That said, doing butt joints with a large gap is not easy. A trick is to back the piece with sheet copper and wash the joint, edge to edge filling in the gap. The weld will not stick to the copper backing.

Rot 911 · 12-13-2004, 07:17 AM

I think I uses .025, but it might be .023 on sheet metal. And like Rick said if you can get a piece of copper behind what you are filling in it will make your welding much easier!

Zeke · 12-13-2004, 07:18 AM

You have to change tips to change wire and .31 sounds thick enough for MIG. but I forget (need some coffee). What I wanted to say is that if you remove the nozzle, you expose the tip which is electrically charged when you pull the trigger. If it touches, it will burn the brass and ruin the threads. Also, your gas won't shield the weld and it will splatter like crazy.

Better to adjust the voltage and series tack weld in there.

dmcummins · 12-13-2004, 07:18 AM

I went to .023. I had alot less burn through.

Argeo · 12-13-2004, 07:29 AM

Thanks guys. Everything you said makes a lot of sense.

I unfortunately can't get a piece of copper in there for backing.

It is a small area like an inch long on a 90 degree angle so maybe I will just hack it and throw a small patch over it. It won't be seen when the door is closed and is so small I don't think it will be too noticable unless someone was really looking for it. Other side I will just be more careful.

Thanks,

David

jpnovak · 12-13-2004, 07:31 AM

Yes, use the thinner wire. yes, a Cu backer helps.

If you have a large gap here is a trick. Set the voltage low and use a lot of wire stick out (distance of tip from surface) Next, lay a small almost cold bead down both sides of large opening. Now increase the power and place a U shaped bead dragging the pool across the open area as you go. Weld across one side, release trigger and pause for a second or two. when you just see the the pool start to cool (dull red glow) start the next crossing of the gap. The bead you laid on both sides will act as a heat shrink and will help prevent burn through from the excess oxygen blowing through the gap. When finished you can grind it out and then make a nice bead pass across the whole area blending it in for a really smooth surface.

YOu can slide the shield cup back so the tip protruds out a bit. this will give you some clearance for tight spaces. Do not remove it. As Milt says, the tip may touch and short.

If you are careful you can cut and modify the shield cup to a smaller diametery. Just have a spare in case you mess up.

Argeo · 12-13-2004, 07:47 AM

Great stuff JP. Thanks.

Porsche_monkey · 12-13-2004, 07:52 AM

Rules of Thumb:

Less stick out more pentration (hotter, burns through)

more voltage more penetration

more wire feed speed more penetration

more CO2 in the mixture more penetration

larger diameter more more penetration

slower torch travel more penetration

pushing the weld (ie point ahead of the puddle) more penetration.

(Seems to me I have penetration on my mind today)

Therefore for butt welds on thin material:

Argon (not CO2), long stick out, low wire feed speed, smallest wire available, keep moving (lots of short tacks), point the wire into the puddle as you move. Welding vertically and travelling down where possible should also help.