I always topstitch around the top, opening edges of any bag I make and I instruct this in my sewing patterns as it makes such a difference to the finish. The topstitching gives a neat, professional finish to a handmade bag as well as being functional, in that it keeps the lining in place and stops the stop edge from being all floppy and going out of shape.
Once you’ve pushed the lining down into the outer bag (pull-through and turn-out method which I’ll elaborate more on in another post) use your fingers to roll the top edges to get the seam sitting neatly at the top edge, or just inside the interior. Keeping any handles and tabs in the correct upright positions, place the bag opening over the narrow edge of your ironing board if it will fit (or place a tailor’s ham or rolled up towel inside the opening). Carefully press the bag’s top edges, all around the opening, adjusting the edge as necessary as you go around it to ensure the seam sits neatly at the top. It’s a good idea to use a pressing cloth, so as not to leave any marks on the fabric. Once you’re happy with the neatness of the bag opening, it’s time to topstitch it.
Remove the sewing table to reveal the free-arm (narrower sewing table) and place the bag opening over it. The right side of the bag should be uppermost. Start at a side seam, sinking the needle directly into the seam joining. Pull the threads out to the back to ensure there’s no slack. Adjust the stitch length to 3 or 3.5 – the thickness of the layers require a longer stitch and it looks nicer as well. Line up the edge of the bag with the correct seam allowance. I usually use a 1/4” seam here. Stitch a couple of stitches forward and then back-stitch a couple before going forward again, to secure the stitching. Carry on around the bag opening, ensuring you keep any handles, tabs or flaps out to the right and straight so that they don’t get caught up in the stitching. When you stitch over any thicker areas, which have the ends of the tabs or handles inside the top edge, increase the stitch length slightly to cope with the thicker layers and to keep a consistent finished stitch length.
Tip: Use a matching thread, if you’re new to topstitching, (just a slightly darker shade than the fabric) this way it won’t show up any flaws in the stitching too much. Once you get confident with the topstitching, try using contrasting threads which really show up against the fabric as it adds a lovely decorative feature.
Once you’ve stitched all around the bag opening, and come back to the seam you started at, stop right on the seam and back-stitch a few stitches before going forward to stop at the seam again. Remove from the machine and very carefully snip off the excess threads as close to the fabric as possible.