With all of those tubes cut, it was time to start welding. I started by installing the horizontal pieces. This was just a matter of measuring the height on the left and right side and tacking the tube in place. After I had installed the first vertical tube I remembered about how I should have drilled a small hole to allow the air inside of the tubes to ventilate. A nice reminder came when i couldn’t close up a vent hole that kept opening itself at the junction of the two tubes while I was welding. To fix the problem, I just drilled from the outside of the original vertical seat tube all the way through to the inside, so that the hole would fall inside of the new horizontal tube. When I had finished the whole seat, I just filled up the new outside hole by welding.
I wanted to finish both the seat and the headrest for the first one so that I could make sure I didn’t have any unforeseen problems. Then, I started on the second seat. There are two lessons that I learned that I will share in case you are planning a similar modification. First, don’t weld the new horizontal tube in place until you have drilled the holes in the old top horizontal and filed them to the final shape. With the new horizontal in place, you can’t get the drill and unibit in there to drill from the bottom up, and since the unibit has such a short reach, you can’t get it from above either. You can disregard all of that if you have a right angle drill.
The second lesson is that it is much easier to grind the paint off of the original top tube before drilling the holes for the verticals, and it probably takes much less life out of the scotchbrite disk to do it that way.