I said I would post a tute of the next zipper I did in a T Shirt so here it is...
Here's the shirt after the zipper... I could not get a good before pic for some reason...
And this one is not too great...
It's just a long sleeve T. Good fabric though. I use a separating zipper. This one is 21" and it's a #3. I get them off the Internet. http://www.zipperstop.com/index.htm
I just have to have my riding shirts so that I can get them off or at least unzip them a ways just to be more comfy when I'm walkin around after I get where I'm going.
First cut the shirt up the front. To do this lay the shirt out perfectly flat, get a straight edge, make a line up the centre then cut. This one is off centre to avoid the logo but it doesn't matter, the zipper installation is the same. Don't pick up the shirt. Leave it lay there and go directly to the next step. That way the shirt and the cut is still even.
Cut two pieces of NON bias binding. Non bias because you don't want it to stretch. This way it will stabalize the t shirt fabric as you sew and the zipper doesn't stretch anyway. Avoid using anything slippery, it makes it much harder. I use the selvages I always cut off of fabrics. This proceedure also will ensure that the two sides are the same length
Cut two the EXACT same length with about 1" extra at top and bottom and pin the raw edge of the strip on TOP of the edges of both the cut edges only about 1/4" overlapping, or the aprox width of your stitch. I use a seam overcast stitch or a zig zag stitch if you want. Make sure the top and the bottom of the shirt edges match when you're done pinning. You will be sewing the raw edge of the shirt to the raw edge of the strip.
Now sew the strip on like so, It should look something like the pic below when you're done
As you sew do not remove the pins till you get really close to them. This will ensure that you won't stretch the shirt. Use the strip and the pins as your guide so that you end up with the exact same length that you pinned. Hold the fabric of the shirt and the strip smoothly as you sew keeping the overlap even. When you get to the last pin resist the temptation to remove it till you get right to it. Otherwise the shirt will stretch and you do not want that.
Here's what it looks like when you flip it over.
Here's what it looks like when you fold those newly sewn edges under. Nice and clean and now it's ready to sew the zipper in.
Fold the extra tab of the strip over then fold the whole strip over all toward the inside of the shirt...
then you're ready to place the zipper and sew it. Open the zipper into two pieces. I leave more at the top than it shows in the pic below cause I like an opening there. I leave some at the bottom too. Using your zipper foot, begin to sew closely and evenly along the edge through the folded over t shirt and the zipper. Don't worry if you don't catch the ends of the strip. You will take care of them later. Try to make sure that the strip is hidden as you sew. Also if you want to, lean the tabs of the zipper, they are at the top, toward the inside and sew them down as you apply the zipper so that they dissappear under the edge of the shirt.
Here's how it will look on the inside when you get one side sewn in. Don't forget that when you get toward the bottom end where the slide is, keeping your needle in the fabric, raise the presser foot and slide the slide up out of the way then drop the presser foot and finish sewing the bottom end of the zipper. That is much easier than trying to sew past it.
Next, zip the zipper back together a few inches or all the way. If you start at the bottom like the pic shows then just a few inches will be fine. If you want to start at the top neck edge close it all the way. Lay the other side against the zipper taking special care to match the bottom, or top, edges. This is why you went to all this trouble to get the top and bottom edges EXACTLY EVEN. Start sewing just a stitch or two below, or above, the zipper tape and don't back stitch. If you get it crooked or uneven it will be easier to pull out and start over. You will go back later to finish all the ends. Sew only about an inch or so and hold it up or lay it flat to check it. If it's even then you can unzip the zipper and continue sewing that side.
Luckily my edges are nice and even. Top and bottom. If you follow these proceedures you simply can't get one side longer than the other.
Finish off the edges and add an extra row of stitching about 1/4" away from the initial row. You can pretty much self explain how to finish the top and bottom edges by the looking at the contrasting stitches in the pic below. I like to lean the tabs of the zipper inward so that they dissappear after it''s sewn and remember to fold over and hide the ends of the strip too. Sometimes they dont get caught when you initially sew the zipper in.
Not too bad a result. I hope someone gets some use from this..