All quilting patterns are written to be sewn using a 1/4" seam allowance. Most machines have a 1/4" foot that can be purchased for them. But, not all 1/4" feet are created equal. If you are having difficulties making all your piecing line up, you should double-check the accuracy of your foot. Most of the troubleshooting we do in the shop for customers regarding patchwork issues has to do with an inaccurate 1/4" seam.
We have a little tool that will help you with that. It's the Perkins Perfect Piecing Seam Guide.
Here's what the actual guide looks like.
Slip the guide under your foot and gently lower your needle into the hole. Make sure the guide is straight and lower your foot onto the guide.
So, what if your foot doesn't line up with your seam guide? If you have the ability to move your needle position, do so until everything lines up. WRITE DOWN THIS CHANGE SO THAT YOU DON'T FORGET! (Yes, I'm yelling. It's that important). If you can't change the needle position, you can make your own "jig" for your 1/4" seam. You can purchase adhesive-backed moleskin in the foot care department of your pharmacy and cut a piece off and place it next to the seam guide. When the seam guide is removed, you will have a little "fence" to place your patches up next to. Or, in a pinch, you can grab a stack of post-it notes and do the same thing. You want to position your "jig" as close to the foot as you can, making sure not to touch the feed dogs on the throatplate of your machine.
After you have checked your foot, now it's time to check your real seam allowances. Cut (3) pieces of fabric 1-1/2" wide. I cut mine 1-1/2" x 3-1/2".
Sew the 3 pieces together to create a mini rail fence block. Press the seams open or to the side and measure the width of the block. It should measure 3-1/2" wide. If it doesn't, re-check your foot, measure your actual seams, review your pressing and try again.
By ensuring that you are piecing with an accurate 1/4" seam, you are well on your way to perfect patchwork!