I'm making a pair of pants now with a lot of pockets, and I wanted to do something different with some of them. I came up with the idea of a pocket with an elastic opening, and a friend, seeing it, gave it the name of Sphincter Pocket. This Instructable will show you how to draft a pattern for this pocket so you can make it whatever size you want, and then construct it either to add to clothing you're making or clothing you already have.
Step 1: Draft the Pattern
Pic 1: First draw a shape in the size of the finished pocket. It doesn't have to be a rectangle, but it should have no concave edges or thin points. A circle or triangle would also work. Remember to draw a circle where the sphincter hole will go.
Pic 2: Cut it out. Decide where you want the seam to be - there will have to be a seam as the pocket is going to be bigger than the flat pattern. I chose to have the seam be at the shortest point, the top of the pocket (see note on pic).
Pic 3: Cut along the seam line. Then start 'slashing'. Make cuts that start from the sphincter hole and go up to, but not through, the edge of the paper. This is ticklish - if you do cut through at some point, it will make the spreading a bit harder but it's not the end of the world.
Pic 4: Make these slices in one entire half of the pattern. Try to keep the cuts relatively evenly spread out over the edge of the pocket generally. There's a lot more pocket edge than sphincter hole edge so you may run out of sphincter hole edge before you get half way around the pocket. This is OK; cut some of the slashes starting from the edges of previous slashes. This is clearer in the pic.
Pic 5: Draw a straight line on another piece of tissue paper. This will be the center line of your finished pattern. Lay the slashed piece along the new line matching up the centers, and tape it down. Spread the slashed pieces apart (there will be some wrinkling near the edges, where the slashes end; this is OK) one by one, and tape them down.
Pic 6: Continue spreading and taping until there is no more to tape. You'll end up with a rather wing-like shape. The edges of the sphincter hole are now little more than a series of dots at the tips of the 'feathers'.
Pic 7: Trace around the edge of the wing shape to solidify the pattern piece edge. You'll need to connect the dots of the sphincter hole for the inside edge. Be more concerned about getting a nice curve than about getting exactly to the line of dots, as they are usually somewhat uneven at this point.
Pic 8: Trace around the edge again, to indicate the seam allowance (the part that will be folded under in the finished pocket). Leave 1/2 or 5/8 inch of seam allowance around the edges, and 1/4 inch at the sphincter hole edge.
Pic 9: Cut along your seam allowance lines and your pattern is complete. Whew! The hardest part is done now; the rest of the steps are much easier.
Step 2: Cut Out the Pocket Pieces
Pic 1: Lay the pattern on top of the fabric, with the pattern's center line on a folded edge of the fabric. (This folded edge should be parallel with the grain of the fabric, or to put it another way, parallel with the uncut or selvage edge.)
Pic 2: Cut it out!
Pic 3: Cut the facing piece. Unpin the pattern and lay it out again, on the same fold, but as shown mark a facing cutting line about an inch and a half in from the sphincter hole edge. You'll be cutting on this line for the facing so you don't need the whole width of the pattern to be on the fabric.
Pic 4: Cut the facing piece out. Carefully cut along the facing edge under the pattern without cutting the paper. This edge doesn't have to be very accurate so don't worry if it's Off.
Step 3: Stitch the Sphincter Hole Edge
Pic 2: Pin the long edge of the sphincter hole together, pocket piece and facing.
Pic 3: Stitch this long edge together. Remember to use a 1/4 inch seam allowance like you made the pattern.
Pic 4: If you have a serger, you can finish the remaining edge of the facing. If not, you can turn the edge under a quarter of an inch and stitch, or just ignore it - it will be inside the pocket and not visible from the outside anyway.
Step 4: Stitch the Pocket Together
Pic 1: Open out the facing and the main pocket piece at each end, and bring them together. Matching the seam, pin the edges together.
Pic 2: Stitch up to about 3/4 of an inch from the seam on each side. This will form the hole that the elastic cord will go through later. It's not easy, yet, to see how this works, but it will be clearer later on.
Pic 3: Finger press this seam you just made open, including the part that you didn't sew.
Pic 4, 5, 6: On the front, topstitch a short distance from the seam to keep the seam allowances folded back on themselves.
Pic 7: Fold the facing around the pocket piece to the inside, so all the seam allowances are tucked inside.
Step 5: Elastic Cord
Pic 3, 4, 5, 6, 7: Using a safety pin on the end of the elastic cord, feed the cord through the tube you just created.
Pic 8 & 9: Pull the cord up as tight as you want and make a slip knot. Your sphincter pocket is nearly complete!
Step 6: Finishing the Edges
It will also be easier to stitch it in place if you press the seam allowance to the inside in advance. The stay stitching will help in this respect too, as you can pull one of the threads to tighten it just a little and encourage the edge to fold to the inside as you press.
Step 7: Attach the Pocket to a Garment
I also made a second, smaller pocket for the right side and that's down near the ankle. The 4th picture is of this one, close up. I gave this one square corners instead of rounded, just for the variety of it. These pants are all about variety - like life!