Leather appliques add interest, information or special effects to clothing that might otherwise be very plain. It is not uncommon to see these appliques on leather jackets, trousers and hats, and also denim fabrics. You can machine sew these appliques on yourself with some basic understanding of the special characteristic of leather that make it different than sewing on regular cloth fabrics.
Cut the applique design to the exact configuration you will be using.
Apply stabiliser to the back of the applique. Trim the stabiliser so it will not show around the edges. Use a fabric glue stick to spread adhesive on the back of the stabiliser. Position the applique on the fabric where it is to be sewn and finger-press in place.
Select a thread that is a heavier weight than you usually use. Lighter-weight threads, especially cotton, have a tendency to break when sewing through leather. Rayon is a good choice, according to Make Them Yourself, which compared threads on leather and found rayon to sew the best, with the least breakage.
Choose the correct machine sewing needle for the project. If sewing leather on leather, a leather chisel needle can be used. If sewing leather onto fabric such as denim, use a regular, round sewing machine needle. The chisel needle slices through the material rather than puncturing it which is good if both are leather, but in a non-leather fabric it will cut the fibres causing a potential for tearing, according to Tippmann Leather.
Test different size needles on scrap strips of leather. Needle sizes 11, 14 or 16 are the most common. The needle must slide up and down easily on the thread you have chosen. If it doesn't go to the next size.
Set the stitch width between 3 1/2 and 6. Using a stitch width of less than 3 1/2 will have a tendency to tear the leather, especially if you have used the leather needle. Test out the different widths with an unthreaded needle to see which one works best for the leather you are using.
Adjust the thread tension. The thicker the leather, the lower the tension setting should be. Thread the needle and test on a scrap to establish the right setting.
Select a zigzag stitch. Adjust the width of the zigzag so it goes at least 3/16 of an inch in from the edge of the applique. Any narrower, and the leather might tear. The density of the stitches will have been established by the setting you made earlier for the stitch width. Test the zigzag on two scraps of leather and adjust if needed.
Confirm that the applique is placed exactly where you want it. Sew the applique on to the underlying fabric. Sew slowly so you can follow the shape of the applique more accurately.
Follow around the edge of the applique being careful to always have the outer stitch of the zigzag only going through the under fabric close to the edge.
Do not use pins to hold the applique in place. This will leave unwanted punctures in the leather.