Like most women I hate bra shopping and have actually taken to wearing sport bras because I am lazy and hate having a bra that digs into the shoulder, too tight, too close in the middle, the straps falling and finding one that looks pretty. So I have been thinking about make ones from scratch or maybe a corset but that is for later, what I am doing right now is customizing bras we can can find. the size of the bra is not really that important what is important is that he cup fits well. The bras I am using are 42D while my sister is more of a 50D. Try finding one that size that is not an arm and a leg and that does not look like something from the 50's is difficult if not impossible.
First step is to separate the bras from the front. Everybody is different the best way to determine size is to measure the space while either wearing a good bra or after cutting the bra hold the pieces up to your breasts fitting comfortably and then have some one measure at the top of the cup. You will need to decide at this point if you wan the clasps in front or back. For myself and my sister it is just easier to have it in front instead of playing contortionist. Then cut the clasps from the back just past seam where the clasps are sewed to the bra. You will have to do this whether you put clasps in back or front. Detach the back strap where it meets the bra remember since you are making the back bigger you will have to move the strap in. At this point the bra should like the one below.
I have found a lot of use for the satin bindings that are used for edging blankets in this case I used a nice beige.
if doing the clasp in the front cut 2 pieces of the satin 3 inch long. Open the satin piece and fold one edge in twice 1/4" (this will prevent any fraying remember that this part will be handled often) then sew them to each edge of the clasps wrapping around. One thing to remember is that one line of hooks and eyes so pull the remainder you should now have pieces that look like this.
In this case the cups fit best at 3 inches apart at the top. Remember that they must be wider apart at the bottom. If you make this center straight the clasps will unhook the first time you move your shoulders as I found out the first time I did this. I tacked it by hand first then used the zipper foot to sew close to the under-wire.
If you are putting the clasp in the back then cut the satin twice as long as you need then leave it folded in half and sew shut. Again remember the bottom needs to be wider then the top when you finish. A good rule of thumb would be an 1" to 1 1/2" inches difference. In this case I used an 1 inch. remember that the final goal is for the center to be flat to the chest if it is not then shorten or lengthen as needed.
I took a tight chest measurement right under the bust then took off 1 inch the reason for this is that the sides are elastic and I wanted a snug fit. I then cut a piece 13 inches long and sewed it with open fold facing up. The reason for this is so that I could insert the strap into the fold then sewed the fold shut. This prevents the end of the strap rubbing into the skin. It will have to be tried on to mark the straps I did not want a T-strap look but I hate having the shoulder strap fall down when it is too close to the side. If you are putting the clasp in back you would cut the ribbon in half then attach the cutoff clasps to the end. You are merely extending the sides.
You now have a comfortable bra with little expense. You can use any bra so long as the cups fit which opens a lot of possibility and means you can pick up the more common sizes like 40D when you really wear a 50D.