Continuing with our custom mount for our Mastercraft Sportsman seats in the rear of our 2004 Toyota 4Runner:
The rear crossbar ties into the stock mounts for the back of the fold-and-tumble rear seat, and re-uses the stock bolts, which have a step underneath the bolt head.
Instead of fabricating the tabs at each end of the bar, Protofab weld tabs were called on. The Protofab tabs are made for 1-1/2-inch tubing, but tightening up the space between the "ears" made the tabs fit nicely on the 1-1/4-inch tubing used for the rear crossbar.
The outer ends of the crossbar sit flush with the weld tab. This doesn't leave much of a channel in which to lay a weld bead. The solution was to bevel both the edge of the weld tab and the end of the tube. This created a nice trough and guiding the weld puddle was easy.
To create an ideal fit, one tab was welded to the end of the crossbar and the other was left loose. Next, the loose tab was bolted into place and the crossbar was fastened down on the welded end. A pair of machinist's blocks helped keep the tab placement symmetrical. Using this method made for an ideal fit.
The loose tab was tacked into place, and then the crossbar was unbolted so final welding could take place on the bench.
A word to the wise, now that we're wiser: be careful of carpet and molding panels even when tack welding! I tacked a little too close and slightly melted an edge of the plastic. It's a small blemish, but it's there.
While the crossbar is sufficiently strong to support the seats and their occupants, it's only anchored at the outer edges. With the stock seats, the seat base actually rests directly on the floor, and the seat back bears a lighter load. Our new seats are one-piece, so some of the load that went onto the floor with the stock seats will now go into the crossbar. What this means is that we'll need to anchor the crossbar somewhere mid-span before we're done, as the two outer bolts don't look sufficiently stout to carry the load they'll now be placed under.