This year, I found a good tutorial online and went for it. This was after I kept eyeing that dang zipper and thinking, in my naive way, that it didn't look that hard. Guess what?! It's NOT HARD - in fact, I would say putting in a separating zipper is easier than a regular zipper! It's much more intuitive, for one thing. There's also much less chance of sewing on the zipper teeth accidentally and breaking a needle.
So I fixed Ben's coat. Then I took a deep breath and cut up my lambswool crewneck sweater. I've been all talk about this project for close to 2 years now (scaredy-cat).
The sweater is a lovely material and color, but I hate to commit to crewnecks because what if I get too hot? Then I have to wiggle out of it, and by this point in winter, I'm getting tired of putting on all those clothes and I want easy layers.
I cut off the sleeves and slit the sweater up the middle. I expect I'll use the cutoff sleeves as filler for hotpads. I finished the newly-raw edges with bias binding. I treated the sweater as if it was made of woven fabric; this was not successful with the armholes, which sagged out quite a bit.
Then I put in a bright green separating zipper. I am so pleased with how this turned out! Especially with my hefty Gap men's flannel shirt from the thrift store.