How do you add a sleeve to a sleeveless tank shirt? Its actually quite a simple process. Its something that I have done with the children in their sewing class.
Turn the sleeveless tank shirt inside out and lay it down on top of a piece of folded fabric. The folded line should be the continuation of the shoulder seam. You will see that the shoulder seam of the tank angles downwards slightly. Continue that line marking with chalk or a pencil on the fabric for the desired length of your sleeve.
Follow the line of the arm scythe area and add on 2 cm at the bottom for the seam allowance. Cut out two sleeves.
The shape that you should get should look like the pink sleeve in this picture.
Stitch the under arm seam of your sleeves. With the right side facing outwards insert your sleeve into the armpit area of the tank top so that the right side of the sleeve is facing the right side of the tank top.
Align the under arm seam of the sleeve with the side seam of the tank top and pin all around the sleeve head.
This is what it should look like before going to sew on the machine.
Stitch all around the sleeve head using a narrow zigzag or stretch stitch if the material is a knit, if it is a weave you can use a regular straight stitch.
Make sure that you do not catch the sleeve under your stitches. Make sure that you are only sewing on 2 layers and not on 4.
Once you have completed sewing it, pull the sleeve towards the inside of the tank top.
Pin the other sleeve in place in exactly the same way and sew it.
This is what the finished product looks like.
It is quite a simple technique and allows for many upcycling options.