I officially do not like making fly zips on trousers. Give me a nice invisible zip any day. Alas, my current trouser project calls for one. On Sunday at 10pm I decided to finally call it a day (or night!) and wait until my next dress making class.
So, what was the problem? well, if you don’t millimeter perfect line up the centre front of each side of the zip absolutely straight it will create a pucker at the bottom of the zip. In other words, it (the zip) won’t fly unless your wings are straight, and lined up together.
I also found it more than a little confusing that there were so many techniques to make one. So here is how my tutor explained it to me (several times, before I could get my brain to figure it out). The left flap (it would be on your left when wearing the trousers) gets folded inwards (and press with steam) but with an extra 5mm instead of just where the curve ends at the bottom the flap.
You then attach the zipper on this side by first lining it up from behind and attaching it to the back, but not the front. This means if you wanted to you could pull the flap back round. Then you top stitch from the front through the fabric, the flap and the zip, close to the zipper teeth.
Then the bit I took ages to understand. Fold and press back the right flap (just to where the curve ends), then line up the centre front until it covers the zipper teeth. It drove me mad that no one was showing a good set of photos of the front AND back. So here is what it looks like before I sew.