Trousers zipper fly tutorial

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The zipper fly-front is a traditional zipper application for men’s trousers. Nowadays, most of women’s pants have the same kind of front closure. The only difference really is in the plackets lap direction: in women’s clothes it laps right over left (as shown in this tutorial); and in men’s wear it laps left over right. And even that doesn't seem to be a set rule anymore, since most RTW companies do zipper flys on women's pants where left laps over right. Same goes for jeans. 

PS This is no “entry level” self-fly tutorial.

If your trouser pattern has a self-fly facing cut to your pant leg, you should redraft that part and also cut out a separate fly facing. New fly facings width depends on how wide will your topstitching  be and how big are your seam allowances. Normal width of zipper fly topstitching is 3...3,5cm, adding 2cm seam allowances we get 5...5,5cm.

Fuse fly shield and facing if necessary. Sew the fly shield and finish the raw edge of it. Clean the raw edges of crotch, inside leg seam and fly facing as shown below.

Place leg pieces right sides together on top of each other and stitch the front crotch seam, starting from the notch and finishing 3...4 cm from edge of inside leg.

With right sides together, pin and/or tack and sew fly facing to the right front starting from the bottom marking. Trim and layer seam allowances; understitch seam allowances to the facing if necessary (I always do it on trousers).

Press the facing to the wrong side of right leg. On left leg, fold under 0.5cm of left trouser front going beyond the crotch seam and press. With tailor's chalk, mark a curve for topstitching on to the right front. 

Place closed zipper face down on the right side of facing. Left edge of zipper tape should lie along facing seam and bottom stop should be 2cm from edge of facing (if the zipper has a wider tape, place left edge of zipper tape few millimeters over the facing seam). Starting from bottom, tack zipper in place turning up bottom of left zip tape. Sew the zipper to facing on the right tape. (You may do a double seam, if you think it is needed. In my 10 years of sewing I have never done it. Zippers tend to break before the seams do and to think of all the ripping one has to do to replace a zipper…)

Turn the facing to the inside. Pin and/or tack facing to the front. Starting from bottom, topstitch along chalk markings. Before lowering the presser foot and needle at the start of topstitching, make sure that left leg seam allowances are not caught in the zipper topstitching.

With zipper closed, lay your trousers flat on table. Mark the height of front to left zipper tape. Put the first pin in at the top of left leg, pinning zipper to left leg. Note that folded back edge of left front should be parallel from top to bottom with zippers coil or teeth. Open zipper, pin left front to zipper. 

Working from the inside, position fly shield following along the edge of fly facing. Pin shield in place.

From the right side, tack through all the layers of trousers, zipper and shield. Using zipper foot, stitch close to the edge of left front from top to bottom. Remove tacking.

Pull zipper closed, sew a bar tack at the bottom of topstitching. Working from the left side, sew a bar tack, catching only fly shield and facing. Open zipper, stitch across zipper coil and tape at the waist. If needed, cut of any excess zipper. Remove any chalk marks with a brush or with damp cloth. If chalk marks are still evident, use vodka or rubbing alcohol. All chalk markings should be removed before final pressing.