I have made two T-shirt quilts for people, one using the interfacing and sewing the blocks together with sashing but the second one had so many different sized emblems. I cut them out of the shirts larger than needed, put interfacing on the back of each one and cut them into neat shapes. I used fabric glue to hold them in place, not on the edges, just enough to secure them to a large piece of fabric and then machine stitched them in a decorative manner.
The man who ordered the second one, cried when I had it done, the Harley Davidson shirts belonged to his wife. The first one still hangs on the wall of the woman who went on bicycle marathons, I was told.
Carol J.