Ha ha! It sounds like a The Big Bang Theory title, but this post is about a very practical and recurrent process to transform one regular t-shirt into a piece of clothing that actually fits us girls better. I love collecting my favourite bands' merch, but too often they do not have the girlie version, so I have to customize it.
I think that the pictures speak for themselves. We must use a jersey neddle in the machine and sew the seam with a very narrow zigzag for elasticity. Next to this stiching, we will make a wide and short zig zag, and we will cut the seam allowance reeeeally close to it. In that way we will have something similar to the job done by sergers, only we have to make it in three steps instead of one.
For the sleeves and bottom hem, we will roll the fabric towands the inside twice (1.5 cm each turn), and we'll machine-stitch it with a jersey double needle.
Finally, we'll remove the original t-shirt's neck and sew it again in place but in a deeper cut line. We will place the neck elastic band in the inside, under the folded neckline. We will machine stitch it with the double needle too.
And do not forget the ironing in every step.
This procedure is the same I use to adjust my boy's t-shirts when they are too big, minus the neck adjustment.