[Warning: Long post with many photos ahead. ]
There are many ways to insert a fly zipper. There is not a set "right" or "wrong" way, because most instructions get to you to the same place, eventually. The difference is in ease of construction, which is a subjective thing. What may be "easy" for me, might not be "easy" for you and vice versa. The main thing to remember is to be open to trying a new method. If it doesn't work for you, keep trying different methods until you find one that does work for you. I had not previously tried BWOF's instructions for the fly zip until earlier this month. My previous method was based on the Reader's Digest Guide to Sewing method. Many of the Big 4's instructions follow similarly to BWOF's to a point, but finish differently, either with or without the underlap. I'm not sure who would want to wear trousers without the underlap, but whatever makes people happy is fine with me.
Let's take a look step by step at each method and compare ease of construction. The BWOF sample is in red and the Reader's Digest sample is in white. I did not show any basting, but you certainly could (probably should) for each step to make sure things stay where they're supposed to during the stitching process.
Step 1: This is the same for both methods. Stitch the crotch seam, from the inseam to the end of the fly as indicated on the pattern. Press the right fly facing to the inside along the center front line. Press the left fly facing to the inside 1/4" to the left of the center front line - you can see that in the picture below - you can see the excess fabric to the left of traced CF line on one side of fly opening.
Step 2: This is where things start to differ. Burda: Stitch the zipper, face up, to the left side of the zipper opening, using a zipper foot and stitching close the the facing fold and zipper teeth. RD: Place zipper face down on right facing that has been opened out, aligning zipper with the CF line. Stitch down the center of the zipper tape on the right, furthest from the CF line.
Step 3: Burda: Pin zipper opening closed, aligning CFs. RD: Turn right front zipper facing and zipper to the inside.
Step 4: Burda: Turn the work over to the inside; extend only the right facing and zipper, and stitch zipper to facing only. In the second photo, you'll see the piece on the machine with the facing extended; stitch only through the facing, not the front of the trousers. RD: Topstitch right side of trousers on the top stitching line. This step is where much of the trouble begins. Note that by this step, both sides of the zipper tape are secured in the Burda directions, but only one side in the RD directions.
Step 5: Burda: From the right side, topstitch the right front of the trousers, along the stitching lines. (It is there, sorry you can't see it in this photo.) Remove pins holding CF closed. RD: Baste the left zipper tape to the left zipper opening, aligning the fold along the zipper teeth. Note the second photo below. It is very difficult to baste, and subsequently stitch this by machine. The topstitching from the previous step catches everything underneath and it's hard to get those last few stitches in. I had to remove a stitch to even get it stitched halfway decent.
Step 6: This is the same for both. From the wrong side, pin the fly underlap in place, over the left zipper tape. If you do no other basting, this would be the one place where it's a good idea. You'll be stitching from the other side in the next step and those pins underneath will probably catch on the feed dogs and who knows what else on their trip through the machine.
Step 7: Burda: (This isn't so much tricky, as hard to visualize, follow the three pictures below after the comparison picture.) Turn the facing with the underlap pinned to it over, so that you can stitch from the other side of the facing. Photo 1, shows me starting to turn it, photo 2 shows it flipped over. Photo 3 shows the piece actually at the machine; the stitching is closer than that, but you get the idea. The piece is to be stitched close to the existing seam, a little further over to the left than where the machine foot is in the photo. RD: Stitch through all layers, facing, zipper and underlap close to zipper; remove basting.


That's it. You're done with both methods. Here's the final picture. Both zippers are closed in the picture. Notice there's a bit of weird wrinkling at the base of RD version. Not something I'd wear. It says "homemade" not "handmade". The Burda zip is flat and smooth. Furthermore, the Burda zip is installed with only 4 seams, and can be done without any basting if you're a bit crazy like me and like to take risks. I didn't do any basting for the Burda in these samples.
At this point, you could do a bartack at CF where the topstitching ends. You can also baste across the top of zipper tapes, *with the zipper unzipped* and cut off any excess zipper above the top edge of the trousers. This is easier than shortening the zipper from the bottom and gives you the security of the original zipper stop being in place, rather than the zigzag tacks that are sometimes used to shorten zippers.Parting Shot: My latest treasure from Australia has arrived! I'll do a whole post on it next week, showing some of the pages and comparing it to the current BWOFs. It doesn't have it's pattern insert, but upon close inspection, it looks like it had one at one time. This one is from August 1958.






































