I thought I would write up my own instructions for making one of these. (Because I do it slightly differently to everyone else out there...more shortcuts, less professionalism...lets face it I am a lazy seamstress...)
This makes one pouch approximately 5.5" long, 3" tall and 1.75" deep. Its pretty adaptable though.
2 pieces of outside fabric, 5.25" tall by 9.25" wide
2 pieces lining fabric, same size
2 pieces fabric to cover zip ends, 4" by 1.25"
2 pieces of fabric to make zip pulls with (optional), 4" by 2.5"
Note: All seams are sewn with a 3/8" seam allowance. (Sorry, I've never been able to figure out how to type fractions on a mac - if anyone knows, please educate me!) Always backstitch at the start and ends of seams. Use a short stitch length.
1. Cut out all your pieces.
2. Take your zip covering piece and fold it over 3/8" either end and press. Then fold the whole thing in half and sandwich it over the end of your zip. Sew in place. Do the same on the other end.
3. Take one outside and one inside piece and fold and press 3/8" of the top of each piece over.
4. Sandwich these with the zip between them, so that the inner fabric is facing down and the outer fabric is facing up. Pin in place if you feel the urge...
5. Starting 3/8" from the end, sew down the sandwich, stopping 3/8" from the end. (I forgot to leave the 3/8" in mine and had to unpick it afterwards.)
6. Do the same for the other side of the purse, making sure the outside fabric is facing the opposite way - so that the top of your pattern is at the zip.
7. Trim off the excess zip-covering fabric so it's flush with the other fabrics.
8. Open the zip halfway. VERY IMPORTANT STEP!
9. Take the two pieces of the outer fabric, place them right sides facing, line up the bottom ends of them, and sew them shut.
10. Do the same with the liner fabric. If you like with the inner fabric, you can leave a 3" gap in the middle of this seam - you will use this to later turn the whole bag the right way out. I just sewed it up, then used the seam-ripper later to open it. You now have two wrong-sided open-ended tubes, attached in the middle where the zip is.
11. Make your pull tabs. (Optional) Take the pull tab fabric and fold and press two 3/8" folds along the length of it. Then fold the whole thing in half lengthways and sew it shut. Fold it in half width ways and press. Make two of these.
12. Sew the ends shut. To do this, line up the bottom seam (made in step 9) with the zip, so that half of the purse fabric is sticking out either side. Insert the pull tab into this, right on the centre of the zip. Stick a pin in there to hold it in place.
Pinning in place
13. Flip the whole thing over and lift the liner fabric out of your way, then sew through the outer fabric, including zip and pull tab as pictured, removing the pin. Go over the zip part a couple of extra times to strengthen it. Do the same on the other end.
14. Now do the same for the inner fabric, including sewing through the zip yet again (i.e. lift the outer fabric out of the way in the same way you did the inner in the previous step.) You now have two connected bags that are inside out.
15. In the picture above, have a look at the bottom section - this is the outer fabric. Look at the crease that runs from the near corner to the corner at the back left of the photo. You are now going to pinch the seam on the outer fabric, so that the seam you just sewed lies on top of that crease, making a little triangle at the corner.
16. Mark a line on the triangle you just made, 1.5" from the point of the triangle and at right angles to the seam. (Marked in purple below.) Sew along this.
17. Do the same for the other side of the outer fabric - so two triangles are sewn.
18. Cut off the excess fabric in the triangle and go over the raw ends with a zig-zag stitch.
19. Now do the same to the other end of the outer fabric, on both sides. Then repeat the whole process on the inner fabric. I seem to have forgotten to photograph this part, but to be honest it looks very confusing and you are doing exactly the same thing on all 8 corners anyway.
20. Rip a 3" hole in the bottom of the inner seam if you need to and turn the whole shebang inside-out.
21. Sew the seam shut - it looks much better if you hand-sew it, but as you can see, I am lazy and did it on the machine.
Et voila, a finished box bag, with no visible seams in sight!