This entire blog post is dedicated to piecing the corner part of the blocks in the Violet Quilt Pattern. You might wonder why this one step merits its own blog post - if you are an experienced quilter, you can probably skip this one. But if you are a newer quilter or if you struggle with getting a nice scant, quarter inch seam, I want to make sure we start out on the right foot.
When you are making a quilt, you want to use a SCANT quarter inch seam allowance. What this means is that if you measure your seam allowance (prior to pressing), it should be just under 1/4" wide. But, once you piece your fabric, the seam allowance plus the little bit of width that the fabric adds should be EXACTLY 1/4". If you want more info, Amy at Diary of a Quilter has a great blog post all about it.
Most likely, your machine came with a 1/4" piecing foot or you have picked one up along the way. If you are using that sewing machine foot with the default setting on your machine, you may or may NOT be getting a scant 1/4" seam allowance. It would be nice if everything just worked the way it is supposed to, but that's not always the case.
I sew on a Janome MC6600P. It is a fabulous machine that I love to death, but the 1/4" foot that it originally came with is just not that great. The shop that I purchased the machine from recommended that I purchase another foot called the O2 foot - it is also made by Janome and cost less than $20. It is fantastic and gives me a scant 1/4" seam allowance every time.
Your machine might do a scant 1/4" seam perfectly without any adjustment, but you may benefit from a new 1/4" foot or you just might need to move the position of the needle on your machine if you are having an issue.
When we piece our corner pieces for the Violet Quilt, if your seam allowance is just slightly too big, you will end up with two squares that are just slightly smaller than your rectangle.