I think I found a good solution for the seatback tack strip. I ordered a strip of Low-Density Polyethylene from McMaster-Carr. A 3/8″ x 2″ x 48″ chunk of LDPE was only $7.50 plus $5 shipping. And it came the next day, packed in a nice sturdy tube that probably cost more than the shipping charge! This material (the stuff that gallon milk jugs are made of) holds tacks well, and it is tough and flexible. I cut a couple of 3/8″ x 3/4″ strips, and drilled screw holes in it. The ends need to be rather curved, so I dipped them in boiling water to get them soft and bent them to the correct shape as they cooled. Besides the LDPE, I had also tried a piece of that “plastic wood” that is used to make decks, and it did not hold tacks very well.
I also got a lot done on the wooden seat base frame. I needed to make a sort of tongue-and-groove joint on each corner, and I had no idea how to do this without some sort of specialized machine tool. I did a bit of Internet research and found that I needed to make a “corner bridle joint“, and I learned the correct trick to doing it with a table saw. The joints came out nice and accurate. During the next week I’ll do some more carving, cutting, and drilling to get the frame finished.
In the last week or so, I installed new wooden tack strips on the seat. Some of the strips were just 3/4″ x 3/4″ wood strips a couple of feet long, and Home Depot sold wood of the exact same size in oak. To attach those, I re-used the original screws, which were in perfect condition. There were two other strips that were originally make of some sort of fiber material, long since crumbled away. I made replacements from 1/4″ plywood. These had to be riveted in place. The correct semi-tubular rivets were easy to get, but I had to make a tool to properly set them. That was easier than it sounds- I just took a 3/8″ bolt that was lying around, cut off the head, put it in the lathe, and cut a donut-shaped depression in the end.
I still need to deal with the long metal tack strip that runs across the top of the seat back. There is no big rush for that- it will be at least a couple of months before I get the upholstery kit for re-covering the seat.
I decided to try making a new wooden base for the seat cushion. The original had been not terribly well fixed up by a previous owner, and I was thinking of buying a ready-made reproduction. But the reproduction is rather expensive, and I realized that Home Depot sells the same 3/4″ x 4″ oak boards that the base is made from. The base is just a rectangle made of 4 pieces of wood, with some fitted joints and a few holes of various sizes drilled in it.
The seat base springs are attached to the wooden base. I’ll be ordering reproduction springs. The original springs look usable at first glance, but several of the wire rods had been broken or badly worn, and a previous owner had tried heroically to fix it up. But if I re-used them and something later broke, all the expensive new upholstery would have to be ripped up and replaced to repair it.
Last weekend the weather was nice, and I painted the front seat. Later in the week I bead-blasted the metal channel that is attached to the top edge of the seat back. The channel was originally filled with some sort of fiber/leather compound for holding the tacks that fastened the upholstery in place, and I will need to find a suitable replacement.
In the last week or so I managed to sandblast the lower part of the seat and finish fixing the bad welds. With the paint and rust gone, I was able to notice a couple of little cracks, which I welded. The rest of the seat has only light rust (or none at all), and I can clean up the remaining rust with a sanding disk. Weather permitting, I should be able to paint the seat in the next few days.
I also cut some strips of thin plywood which will replace a couple of tacking strips that were on either side of the seat base.