I have 1/4" feet for all my sewing machines and don't use any of them. If I do, I find that my blocks are consistently undersize. This is much worse than a little oversize that can be trimmed a little. Instead I use a regular zigzag foot and my side to side increments to achieve a SCANT 1/4" seam. Very important. A true 1/4" seam is too big and doesn't allow for the space taken by thread and folding. Another thing that has helped is using thinner thread. When I started using Aurifil 50 wt. thread for piecing, the clouds parted and the sun came out! I bought a cone of light grey that works for most piecing and use a cone holder. Only one of my machines doesn't like it (tension problems). Seam size problems get worse the more pieces in the block and thus more seams. Make one whole block and measure it. Then if the block is too small adjust accordingly. You will only have one block to remake. I have to use a leader on my main machine or it eats the thread, makes a bird's nest on the back, eats the point, and tangles with the bobbin. This machine has a thread cutter that holds the threads (perhaps that is what it is for) but I have not trained myself to use it. Maybe it is time! And also maybe it is time to start using starch.