I welded several of these rudder linkages for a customer who builds them for racing kayaks. Each one of them was different, with each being custom designed and built to order. Although all the ones I welded were all solid 316 stainless stock, they had various lengths of rods and combinations of round, or square stock in different diameters / widths. In all cases, the orientation of the pieces being welded was critical.

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The end of the round steel pieces had a really nice hex shaped section machined near the end just behind threads that were formed in the very end. The customer had a trick "yoke" piece he had made on a waterjet, which he installed with a wingnut to use as a reference for getting the orientation just right.

The welding process itself was not that hard. I used DC TIG and 316L filler rod, and a sharpened 1/16" tungsten, with footpedal for heat control. Since the welds were not going to be visible (they would be buried under carbon fiber / fiberglass composite, or in other words buried inside a rudder), there wasn't much reason to try to eliminate the heat tinting, so I let my big gas lens cup sit on the bench on this one, and just welded it with my #8 gas lens cup (with about 15 cfh argon.)

The welder's finger (third hand) came in handy for getting the pieces held in position for tack welding. We used c-clamps and shims as well.