i was updating my progress on this costume yesterday when i realised i hadn't taken any pictures of the zipper-shortening process - and figured this might be useful information for someone.
so here it is: how to shorten a zipper.
"why would you even want to do that, it looks fiddly," i hear you cry. well, when you have a dozen old zippers you bought for cheap somewheres a million years ago, and you find yourself needing a half-dozen zips of varying lengths in order to make a set of coveralls for a ghostbusters hallowe'en costume, you gotta do what you gotta do.
i used a nail file and a pair of pliers to do it.
the thing that stops most zippers from opening at the wrong end - and thus determines their length - is a little piece of metal that clamps the two sides together. it kind of looks like this:
with the flat top part showing on the front of the zipper, and the teeth at either end going through the fabric and bending over the teeth of the zipper. here's a look at the back view:
see the teeth? they're pretty well camouflaged. what you want to do is open up those teeth on one side so you can take the bracket off. i used a nail file to pry them up.
once you've got one side loosened, you can push back on the fabric of the zipper to pull them out. here's a look at the front, you can see the teeth pulling out:
then, grab the bracket with a pair of needle-nosed pliers, and pull it gently away from the fabric.
here it is. you can see the teeth on one side (the side pried open with the nail file) are kind of straight, but the teeth on the other side are still bent.
use the broad part of your pliers to straighten out the teeth.
now the bracket is ready to be re-inserted into the zipper in the new location. push the teeth through the fabric on the right side so they poke through on the wrong side.
then, use the pliers to clamp the teeth closed over the zipper so they're nice and flat.
that's when my batteries died, but it's basically done. just cut off the excess fabric, leaving about 5/8" below the bracket for stability.