Hi Val … I shorten tshirts … I use a zig zag stitch or two rows of straight stitches slightly apart … I don’t do a “double” turn-up as it is too bulky and none have ever frayed.
For instance if I want 2" off I measure 2" from the bottom and pin all round … sew a single hem of 1/2" … then trim off the excess as close to the stitching as possible. This is easier than cutting before you sew.
Give it a try on an old tshirt 
I use to be a machinist ,I made dressing gowns for M&S,night gowns too
And in another job I made M&S jumpers ,I was a skilled Machinist for 6 years,.I did make my own Skirts ,this was in the 60s and 70s.
I have a Overlock machine and Lockstitch,I very rarely use them ,i bought them with the intention of setting up a business but ,i don’t have the patience or Eyesight for it now. They are just collecting dust,!
Thank you myrtle, I don’t have zig zag on my machine. Think I have always been more concerned with the stretchy fabric. I have turned up trouser hems, although I seldom wear trousers.
We used to do dressmaking at school, the teacher described me as slow but sure. I also used to make clothes for me and the boys when we lived in Nairobi,
This is a picture of those times, made all the outfits in photo.
You can do it without a zig zag, two rows of stitching, the zig zag is used between those rows to join them together. So you can leave it out but it may not be as strong.
I’d love to be able to make my own clothes. I’m hopeless at sewing. What a great talent it is.
