The idea of making yarn from t-shirts is not new. I stumbled across it when shopping for yarn on Etsy a few years back. I bought some and then decided to try making my own. I think that the most interesting results come from using tie-dyed shirts, so when I see a good one, I grab it. This was a REALLY good one, purchased at my local Salvation Army Thrift Store for $3.
It has lots of saturated color.
There are several methods for cutting and I'll give you links at the end of the post. Mine is probably the slowest, but I don't have a rotary cutter and cutting mat and don't want to invest.
I've used scissors to hand cut the shirt. It's best if you have something to stretch it on, that will allow it to spin freely. I found an ironing board to be ideal. First I cut off the hem. Then I start in from the bottom, cutting as consistently as possible a width of about 1/2". Spiraling around and around the shirt, cutting until I reach the sleeves.
Below is a photo of the "ribbon" cut from this shirt.
By pulling and stretching, the ribbon naturally curls into a nice sort of tube shaped yarn.
It's a bit stretchy. I think I pulled it under a bit of extra tension when warping.
It looked so cool as a wound warp even before I began weaving.
Here's what it looked like after being woven up.
Here's a link to Mollie Makes and her blog post about making t-shirt yarn.
I've not tried this method, but it looks much easier and faster than mine!
And video version from Trish at UpCycled Stuff: https://www.youtube.com/watch?v=Qq7JX-s0Peo