My sister and I have the same tastes in some clothes in others we are like WTF why would you like that. This is one of them.
But she loved it so time to make it looser and look good. I hate adding triangles to a shirt because nothing shouts "it didn't fit me until now" at least to me. I have seen it done and have done so myself but it is hard to make it look like the original design so I decided to save my headaches and try something new. I had a grey tshirt where the front was messed up with bleach spots but the back was perfect. So I folded it and cut two long trapezoid.
Then I folded the pieces in half lengthwise and laid it on the shirt the narrow side to the top. Bear in mind that I want the piece larger then what I will make the opening and the difference between the top and bottom is less then two inches.
Once it is lined up with the edge I used chalk to mark where the underarm goes then I rounded of the top end. I cut allowing 1/4" to be turned under. Then I cut along the fold of the shirt all the way to the underarm.
I began to pin the piece in place after marking how far I wanted to spread the opening. My bad I got a little enthusiastic about how big I wanted it but my sister was happy she wants to use it with leggings or tight leg jeans. So the opening can be however big you want it to be just mark with chalk. The easiest way was to fold the shirt with the cut edges closed close the material around it with the underarm center joint and the bottom center joint in the right place. Place a ruler inside the shirt and push it right against the center seam of the add on. Then holding at the underarm pull the bottom of the ruler out to the side the amount of inches you want to add. I say use a ruler because it prevents the fabric from stretching out of place and keeps the edge smooth. This means there is no guesswork about the attachments edge. Move the ruler back under where the edge of the fabric overlaps the shirt and begin to pin it in place. The ruler I used is a quilting ruler but any one will do.
When you finish the inside will look like this:
You can see how enthusiastic I got at making this work. The outside will look like this:
There were some more changes first was the length of the sleeve that had to go luckily it was easy to cut off about two inches and hem it up.
Then because she is annoying that way she decided that she need a pocket to tie everything together. It is hard to put a pocket on a plus size person because if you put it straight according to a flat shirt it is going to look crooked once it is on. She came up with a good idea I made a paper pocket then kept adjusting it on while she wore the shirt.
Now you have the finished product:
Next time a little less extreme though the addon will stay the same size actually I might make it wider so it comes out closer to the bust. Did not take long to do for a normal sewer you are looking at 2 to 4 hours only because t-shirt material curls when cut and can be annoying.
