How to Use Tack Welding to Keep Your Work Straight
Kevin is making a stand for his latest commissioned sound sculpture. He used some metal scrap left over from a sculpture he made called Portal ( http://www.kevincaron.com/art_detial/portal.html ) as the "backbone" of this new sound sculpture.
He put the pieces together by shaping a piece of 1/2" round metal stock, cleaning up the "triangles" he gleaned from the scrap pile, and sliding them onto the 1/2" round stock to help define the shape.
He had cleaned up the triangles by getting much of the rust off and making them all the same size with a grinder. Then Kevin put the shaped round stock up on jack stands and slid on the triangles. He then spaced them by figuring out how many triangles he had and how long the piece of 1/2" round stock was and did some math (his math teacher would be very proud!).
One "point" of the triangles was 1/2" wide, so he bent some 1/2" square solid metal stock to run up that side. The other two sides each ended up about 1/4" wide, so he bent pieces of 1/4" solid square metal stock to go on them. They help give the piece dimension, presence and strength.
Now comes the tacking. Once he has the triangles where he wants them, he just tack welds them into place as he adds a twist to the form. He could have oriented all the triangles the same way like a spine, but that wasn't dynamic enough for Kevin.
Once the pieces were all tacked on to the round stock in the middle, he shapes the square metal stock and tacks it into place. Next Kevin attaches the two 1/4" pieces of solid metal stock and the 1/2" square solid stock ("That was a booger!" he says) by tacking them in place.
Finally it's time to come back with a MIG welder and weld everything solidly into place. Kevin welds one section then another, then another, hopscotching around the form, because as you weld, everything wants to flex and move. Taking in a variety of places lets the metal cool sufficiently.
When you tack everything first, you can get a good look at it before you do your finish welding. If one of his sections has, say, flexed a little and isn't quite flowing right, Kevin comes back with a little air-powered cutoff wheel with a 3-inch cutoff disk on it. He hooks it up to the compressor, and now he can get down into the sculpture to cut loose any tacks if he wants to tweak anything to get the sculpture to flow and look right.
Finally, Kevin can stand up the sound sculpture, hang a bell on it, put a little weight on it, even hang from it, just so he knows everything is structurally sound.
Next he takes the sculpture out into the sun, which is nice and bright, so he can walk around it with some soapstone or chalk and mark any welds he missed. Kevin also might use a hammer to make areas flow better.
Taking it outside not only gives Kevin a better view of it. This sculpture is going to be an outdoor piece, so it's helpful to see it in what will be its final environment. Caron says it's a good idea to live with it a couple of days, then bring it in and take care of any mistakes. Then he puts it back outside so he can walk by it and see if anything else needs attention.
Once you're happy with whatever you are making, you can paint it, take it to the powder coater, rust it, put whatever finish you want on it.
So tack it, look at it, tack it some more, make any final adjustments, then do your hard welding, get a finish on it, and you're good to go.
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