It is time to sew some leather. This project will be a combination of some machine stitching for the structural seams and then a lot of handwork to finish up the edges.
When I first mentioned this project, I showed quite a few seam options and talked a bit about the unique concerns of sewing leather garments. Some of these problems are basically created by machine sewing, which is one reason I'll be doing so much handwork on this doublet.
One of the concerns of sewing leather that you don't run into with cloth very often is friction. Leather will build up friction against the bottom of the standard stainless steel sewing machine foot.
There are a couple of options for addressing this. One way I've seen work is silicone-impregnated "parchment" paper, sold in cooking stores. A few years ago, my wife bought me a foot that has been coated in Teflon. They're a bit spendy, but less fiddly than working with sheets of parchment.
WARNING: Not all machines are strong enough to sew leather. If yours is not, you can actually burn out the machine or strip the gears, so if you're at all unsure, I'd say you should handsew or find someone with an industrial machine they can loan you.
I was planning to make a lot of use of what I call the "Arnold" seam in honor of Janet Arnold, who wrote the book where I saw one the first time. In the Arnold seam -- which she documented for a couple of different extent leather garments -- has a piece of thinner leather sandwiched into a seam to protect the stitches from being rubbed or ripped apart.
When I started using that style on some of the test pieces as shown above, I was dissatisfied with the final effect. Instead, I will be using the lapped seam discussed earlier, and in lieu of the Arnold seam, I will use a felled seam which gives strength greater even than that of a lapped seam and also lends a structure to the garment akin to what you would get from light boning.
The felled seam is a simple enough concept. Sewing right-sides together as you would any normal seam, cutting away one side and then folding over and sewing flat the remaining seam allowance to finish the seam.
The examples below were all sewn on the hotrod.