There is a Tutorial on how to stabilize knit type items such as T-shirts on the Floriani Website.
It gives ing=formation on what stabilizers to use and shows how to hoop etc.
There are pictures on the right side showing the different steps.
You can click on the pictures for a closer look at each.
You don't need to use Floriani stabilizer just stabilizers that are similar.
Go to the link below and then scroll down the page.
EastWitch2
I've found that using a fabric call 'poplin', which is even weave cotton or poly/cotton as a cutaway stabilizer works with T shirts. Just make sure that you match up the length-wise grain with the T shirt length-wise grain and it will be good
Cut a piece of stabilizer 1" larger (all around)than your hoop. If your hoop measures 6 x 10 cut your stabilizer 8x12. Press do NOT iron your shirt where the embroidery is going to be using spray starch. Press means to place the iron down on the hand smoothed area. (Ironing is going back and forth- don't do that). Find the center of where you want your design to be and using a temporary spray adhesive, attach a poly mesh for light weight shirt, and a heaver cut away for a heavier weight shirt. In other words, match the weight of the stabilizer to the weight of the shirt. Hoop the shirt along with the stabilizer. If you are doing a dense design on a lightweight shirt, put a sheet of tear away underneath the hoop onto your machine bed, covering the area that will be stitched. Put a water soluble stabilizer on top of the shirt and wet the corners a tiny bit to stick them down or use pins. Stitch your design. When you are removing the tear away from the back remember it's tear AWAY, not tear toward.
You can distort your design my ripping the stabilizer toward the design. Use fray check on the places where you changed colors, broke the thread, or had long jumps. I then generally on lighter weight t's iron on a soft covering to seal the stitches even better. I prefer a product from Gunnold called Cover the Back. There are several on the market and any will work.
I do dozens a month and never have a problem unless of course I've purchased a design that wasn't designed properly for what I'm trying to use it on. This works for me 100% of the time. You might find a way that is better for you. Most of the how-to's have to do with you and how your machine acts.
Thanks for your help...I will have to let you know how it goes....do you need to use a ball point needle? I forgot to ask...