The main purpose of a welt in a seam is to protect the stitches from wear. As an added bonus, the welt can blend into the article stitched or contrast for an extra visual element.
I recommend using a medium firm leather, no thicker than four ounce, but a lighter garment weight will also work well as long as the thickness is even and the back is not too fluffy. This is a good use for the marginal parts of a hide that have minor imperfections.
Step 1: Cutting the Strips.
When making a rolled welt, it is useful to know how you plan to sew the seam. The welts I demonstrate are for hand stitching, so they do not need to be much wider than will easily fold. I am using a piece of galvanized flat iron, purchased at a home improvement store, for my straight edge. It is three feet long and three quarters of an inch wide. Since I am right handed, I hold in place the left side directly on the straight cut side of my leather and cut slowly along the right edge. A sharp knife is needed to not pull the leather out from under the straight edge. If I were to need a wider welt, such as when machine stitching, I use a wider flat steel.
Cut them to length or skive the ends to make longer pieces of welt.
Step 2: Glue
Almost self explanatory, glue the back with a good contact cement. I tried a double stick seam tape, but kept pulling the core out of the welt.
Step 3: Roll
The leather can be folded over without a core, but I find that it makes a more rounded profile when one is added. I use a four cord twist linen thread for the core on most of my welts. The main reason is that I had the roll lying around and it is the correct size(about 210 to 277). Lay the core in the middle of the strip and fold until the edges are flush. Note the use of my little finger in the first photo to prevent the core from sliding through at the beginning. I put tension on the core as I work along the strip which helps fold it evenly. Continue with each strip until they are all folded. The rubber band around the spool of thread prevents it from unwinding when I drop it or knock it on the floor.
Step 4: Mark
Along the folded edge, it is useful to mark a line for the stitches. If you are using the welt in a machine sewn seam, this is mostly unnecessary. However it does help to make sure your core is placed evenly at the center of the fold. I use my thumb nail as a marking gauge to press along the folded edge, about an eighth of an inch in. If you press firmly, this will leave a slight indention. I am sure there is a tool that will do the same thing, but I find that this is accurate enough and I always have it with me.
Step 5: Stitch Holes
Along the crease made by my thumb nail, I punch a series of holes to stitch through. I like to hand stitch the side seams of boots so all my panel elements will accurately line up.
Step 6: Conclusion
As initially stated, Rolled Leather Welt has many uses. The first pair of boots has a yellow welt to set the front and back separate. The second pair uses green bison to make a plain pair of black boots a bit more interesting. The boot bags in the third and fourth photos use the welt mainly for protection, but by contrasting the brown on tan canvas, it adds an element of luxury. The final photo shows a welt that has been widened and skived for use along the edge of a canvas panel.
The uses are many and varied. I hope this helps make your leathercrafting more enjoyable.