This was a mending/repair job on my husband's work jeans. He is a forester and spends much of his time traipsing through brush, brambles, and briars deep in the woods. His jeans take a beating. The front thighs get torn to shreds, but the backs of the legs remain unharmed. Once the jeans get holes in the front, they aren't conducive to woods work anymore, as he'll get scratched up through the holes.
After resigning a few pair to my scrap bin, he got to thinking maybe I could patch them somehow, allowing him to wear them longer, until either the patch or the seat wears out. We discussed various possibilities, and I asked on the sewing group on Ravelry for opinions, and this is what I ended up doing.
First, I cut the back legs out of the first pair of jeans. I just cut along, just inside the seam. I cut out the back pockets, too, but then cut those off of the patch (and saved them for me!). I opened up the inside seam of the legs of a second pair of jeans, leaving the very center of the crotch done, and the lower calf, too (I didn't think my machine could handle sewing through so many layers at the crotch). This left me with flat pants legs. I lined up the crotch shaping to the front of the second pair of jeans and stitched it on with a zigzag stitch. Then, I stitched up the legs again, zigzagging over the edges in place of serging, as I don't have a serger.
The crotch area was the most difficult to stitch: it was such a narrow space and a lot of bulk from the waist fabric.
They turned out pretty good. DH is going to wear these a while before I do the same to another couple of pairs. If I do this again, he wants the patch to extend about 4-5 inches longer in the leg. He is concerned the stitching on the patch on the outer leg will get torn up in the woods, so we'll have to see if he's right.
Overall, I'm quite pleased with this. I'm not a seamstress or tailor in any sense of the words. DH doesn't care that these look a little goofy, though. They are work jeans, after all. At least, if he can get even half the life out of these that he gets out of a new pair, that is a big cost savings for us. He goes through jeans almost at the rate a baby does diapers!