I solved a lot of my 1/4" problems by using a thin thread for piecing. I learned that 50wt 3 ply is too thick for piecing when the seam is pressed to one side. I use 50wt 2 ply like Aurifil for the top, with a size 80/12 topstitch needle. For the bobbin I use size 60 or 70 poly. Most thin threads will be poly as it is stronger then cotton. 50wt 3 ply is great for machine quilting for the stitches to show.