What I have done is pinned it while the girl is wearing it, I have pinned the straps to the back of the bra where the straps will be sewn down. You will want to use safety pins so that the pins will not come out or stick the girl when she takes it off. Once it has been pinned and the girl has taken it off, fold the bra in half to find the center back. Then check to make sure that the straps are both an equal distance from that center back. That way you can ensure that the straps are not too far to the left or the right. Now, since you are not going to want to sew the straps on top of the bra, you need to mark the strap where it will meet the back of the bra. Using a piece of soap, tailor’s chalk, or even a straight pin, mark the strap just where it meets the top of the bra’s back. Place the strap behind the back of the bra and line that mark on the strap just below the top of the bra’s back. Make sure it is the same distance from the center of the back. Do the same with the second strap. Pin the strap to the bra with the straight pins perpendicular to the back of the bra. If you used a pin as a marker for placement of the strap, take it out at this point. Again, fold the bra in half to make sure that the straps are equidistant from the center back.
Sewing
When you sew the strap to the back of the bra, you want to stitch as close to the top of the bra back as possible. Otherwise, the back will not lay down properly and the excess material of the bra back will fall over. You will need to make sure the straps are not twisted and lay flat against the bra back. Sew the straps to the bra with a stitch parallel to the top of the bra’s back. I would suggest that if possible, you stitch across any stitches that show on the back of the bra where the elastic is attached to the bra. You Stitch across the strap a couple of times to make sure that the strap is secure and that you have sewn over the beginning and ending stitches. For security purposes, I would suggest sewing the straps at the bottom of the bra’s back. Smooth the end of the strap smoothly under the back and pin the strap at the bottom of the back. Sew it the same as you did at the top of the bra’s back. Lastly, cut off any excess strap, but make sure the girl tries it on one more time before you cut any excess material from the end of the straps.
And there you have it, you have changed a halter bra to a bra with straps sewn down in the back.
