A customer of ours brought in this favorite bikini top and the underwires were poking out of the armpits by almost a whole inch!  As someone who is obsessed with bra sewing as a side hobby, I can tell you why this happened.  For starters, the manufacturer should have left more space in the channeling so there was at least a centimeter of empty space in the channeling so the wire had the space to bend and flex with the body when worn. Secondly, this client has run this top through the dryer many times and I guarantee the channeling shrunk in that process. I cut down her wires and took pictures of the process so I could show you!

I laid the wire on top of the fabric so you could see how it didn't fit and if you look, I've marked the end I'll be cutting with a small line of sharpie marker. 

This wire cutting pliers is the tool I used to cut the wire on the mark I made. 

Once it was cut, there was a bit of a rough edge. We have these jewelry files in our sewing shop from a beloved great aunt who was a jeweler throughout most of the 1900's.  When she passed away in 1990, these files were some of the many supplies from her jewelry store that made their way into our sewing shop. I filed the cut end until it was smooth.

The end needs a new tip so the metal doesn't cut through the fabric again, so I'm using some supplies I have on hand.  This is UV reactive resin that will need to be cured under a UV light, just like gel nail polish. 

Yes, that is a UV light for painting gel nail polish and I'm using it to set UV resin. 

I kept adding several layers until the end was encased in resin. 

Then I put it all back together in the bra and straight stitched at the top of the channel, which is something the manufacturer neglected to do. 

This whole process took me about a half hour to accomplish and I think it would  have been faster, except that I kept stopping to take photos of the process. There are lots of reasons why you might need to trim a wire, and I found using UV Resin to be a great way to tip the ends.