I recently had to convert another batch of bras to nursing bras and I felt I could improve upon my last tutorial, which I made shortly after Edmund was born. Since I posted it, I've had some lovely and excited e-mails from ladies who have found it to be helpful. Janel of Simply Nel told me how she added elastic to the strap and cup to keep it in place, which makes the bra more like a store-bought nursing bra. I thought it was a great idea and I'm sure you'll agree. Here's the revised, and I think, much-improved tutorial!
I started out by ordering three dozen 1/2" nursing bra clasps in beige, black, and white from Sew Sassy. I also ordered 3 yards each of 1/2" plush elastic in those same colors (at the time I placed my order, the strapping elastic in that size was only available in white, so the black and beige finishing elastic that I got has a picot edge trim on one side -- not a big deal.) I figure this should last me through many more years of nursing.
The ubiquitous "T-shirt" bras that have plastic rings above the cups are ideal for this transformation. If this is the type of bra you have, start by unpicking the stitching at the top of the bra cup. (If your bra doesn't have a ring between the cup and the strap, I address that at the end of the tutorial.)
Next, unpick the stitching behind the slider on the strap, where shown.
At the top of the bra cup, slide on the bottom half of the nursing clasp and pin in place. Zig-zag stitch where you previously ripped out the stitching, catching the loop in back. (For all machine sewing involved in this tutorial, I generally stitch, backstitch, and stitch again, for extra strength.)
Take the top of the elastic strap out of the slider, releasing the plastic ring, and slide it through the top of the nursing clasp (making sure it's facing the correct direction). Re-thread the elastic through the slider and re-stitch where you previously unpicked the thread, as shown. (Don't be like me; make sure you're stitching the correct two bits of elastic together. Yes, I had to do some ripping out during the making of this tutorial!)
Next, thread some elastic through the bottom of the top nursing clasp, as shown. (If you are using a plush elastic, make sure the soft side will be facing your skin.) Stitch in place.
Hook the nursing clasp together. (Don't be like me; make sure the strap is not twisted.) Now, this next part is a bit hard to describe, but just use your fingers to guide the elastic down to the bottom of the bra, where the cup meets the back (as shown). Don't stretch the elastic or make it too loose, you just want it to fit the inside of the bra cup. Pin the elastic in place.
On the outside of the bra cup, stitch in the ditch where the elastic is pinned. A zipper foot will be helpful here.
Then go back to the inside of the cup and trim the elastic close to the stitching. Use a little Fray-Check, if you like. All done!
Now, if your bra doesn't have that handy plastic ring, you can still probably convert it. This bra just had a continuous strap from cup to back. First cut the strap about 1" above the cup, then put the bottom half of the nursing clasp on the strap and fold it to the back to create a loop. Stitch in place.
If you don't mind sacrificing some of the length of your bra strap, you can just do likewise to the top part of the strap. However, if you want to keep its maximum length, cut a short length of elastic or ribbon to create a loop. Thread the top of the nursing clasp through the elastic, then sandwich the cut end of the strap between the ends of the elastic loop. Stitch in place, then proceed as in the tutorial above.
I hope you find this useful! I've been "test-driving" the models and they are super-comfortable. I can't feel the elastic inside the cup at all. Vive la breastfeeding! ;-)