Whether you are sewing patches onto clothing for decorative or practical purposes, the process can be done cleanly and securely with your sewing machine. A free-arm feature on a sewing machine is helpful, as this gives you more freedom to manoeuvre the fabric. But even with a free arm, if you are sewing a patch onto a very narrow sleeve or leg of a piece of clothing, you'll have to open the seam, apply the patch and sew the seam closed again.
Position the patch where desired. Measure from a stationary point to ensure that the patch is straight and even. For example, if a flag patch is being sewn onto a sleeve make sure the top corners of the flag are equal distances from the shoulder seam or the bottom corners are parallel to the bottom hem of a short-sleeved shirt.
Insert straight pins through the patch and into the fabric about every 2 inches, placing the pins so that the point of each pin faces the centre of the patch.
Thread your sewing machine with a colour that matches the outer edge of the patch. Set your sewing machine to a narrow zigzag stitch.
Sew around the edges of the patch, keeping the widest point of the zigzag stitch at the outermost edge of the patch but not extending onto the fabric around it. Remove the pins as you approach them with your stitching.
Cut a square or rectangle of patch fabric large enough to cover the area needing repair.
Fold under the edges of the patch 3/8 inch all around the perimeter. Press.
Position the patch where needed with the raw, folded edges of the patch facing down.
Place a pin through the patch and into the fabric at each corner and every 2 inches around the sides.
Sew on the patch with a zigzag stitch as described for embroidered patches.
When cutting a patch to repair a hole, make the patch large enough to extend to a strong area of surrounding fabric. If you sew a patch onto worn-out fabric, the fabric holding the patch will quickly tear.