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How to Weld a Butt Joint



The Voice: Hey, Kevin. What are you playing with?

Kevin Caron: In my last welding video I showed you how to weld a lap joint. Today I thought I'd show you how to do a butt joint. Go ahead: laugh, giggle; get it out of your system.

Just as the name implies, the butt joint is where two pieces of metal butt up against one another. Great for a lot of different thicknesses of metal, but you have to work the joint a little. You have to shape the joint, depending on how thick or thin a piece of metal you're working.

Here's a great little chart that shows all the different joints; you can get this on Wikipedia; just type in "metal welding joints." This whole page will come up and you can look at it yourself.

Using this little piece of eighth-inch steel, I'll butt them up against one another, then clamp them to the bench and tack them on either end. Then I'll run a little bead down there so you can see how it looks. (clamping)

The Voice: So, you've got the clamp right across the joint, right?

Kevin Caron: Yes. These Kant Twist clamps have a bottom and top jaw, but one of them is bigger than the other, so you've got a nice, big, flat surface to work with; or one with the crosshatches in it to line up a rod.

This one is a little thinner and smaller in dimension. I'll put the thicker jaw on the top of the table so I can get across both of my joints in the metal. You've got to cross whole pieces of metal to hold the joint down flat. Then I'll put the smaller one on the bottom of the table.

The Voice: What if you don't have a Kant Twist?

Kevin Caron: There are lots of different clamps you can use, if you have to. You could just hold it down with your hand, or you could weld it to the table - not very hard; just a little tack on the corner here and there to hold everything still. Afterwards you?d grind off your tack welds and take your piece off. Or you could get a brick...use your imagination.

These are the tools I have here in my studio. How can I make my metal working tools and equipment do what I need them to do? I've always enjoyed making tools do something other than what they're supposed to do.

The Voice: Now, it doesn't look as if you chamfered those.

Kevin Caron: I didn't bother to chamfer these. This is just a closed butt joint, because the two pieces of metal are flat up against one another. It's only an eighth of an inch thick, so there really isn't much metal there to chamfer, and the welder is strong enough to penetrate that eighth inch and weld it all in one pass.

You can do either a closed joint, or an open joint - just like that chart showed. Depending on the thickness; if this was quarter-inch, then I would chamfer the edges a little and do an open butt joint, with a wide chamfer at the top and a small, narrow gap at the bottom. Then I would lay a nice bead down in the center and get all the way into it.

It all depends on the thickness of your metal, whether you chamfer it, U-shape it, or J-cut it. Look at that chart. It's got some good information.

Get your helmet on.

The Voice: What welding machine are you using today, Kev?

Kevin Caron: This is my little Lincoln buzz box. It's called a "Little Tombstone welder". It's an arc welder. This is 6013 rod, eighth-inch diameter, and we're running at 120 amps.

The Voice: So, you just tacked it. . .

Kevin Caron: Yes, tacked at both ends to keep it from spreading, then I'll put a clamp in one spot so I've got a good ground; then run a bead down through there.

(welding) That's a little warm. Now we'll turn it down to 105 amps.

(welding) Let's chip the slag off; see how we did. Ooh, need a little more practice there.

You can see this is where I started at 120 amps. It started to burn through and melt the eighth-inch plate, so I stopped, went back to 105 and started over here, running a bead down.

This looks pretty good. Here?s where it started to melt through again, because I've only got it clamped on one end. As I was welding over here and the metal was heating, it was lifting up off the table. So, instead of the table sucking some of the heat out of the weld, so I could make a decent weld here, now it's up in the air.

All the heat is staying right in the middle where I'm welding. Even at 105 it's too hot and started to blow through. So, 90 amps probably would have been better to do this piece with. But, hey, that's how you learn. You play, practice, make mistakes, and start over.

Let's look at the back. You can see the discoloration in the back of the metal. This is from the 120 amps, where I first started. This is from the 105 where I made that nice, long weld. You can see how much heat discoloration there is. You can see how the weld was starting to come right through the back side of the metal. You can see full penetration all the way down through the metal, coming out the other side. It should be a pretty good joint.

So, that's how to weld a butt joint, just by playing around a little.

Wikipedia: it's a great place to go for information on stuff like this. Just type in "metal welding", or just "metal" and "welding", and you'll get lots of good information.

I'm going to go find something else to do here in the studio. I'll see you next time.

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