Why Do You Need a SCANT Quarter-Inch Seam?

If your seams measure exactly a quarter-inch from the stitches to the edge of the fabric, your blocks will come out just a tiny bit too small. This happens because when you press a seam after sewing, the top layer of fabric is folded over to one side. This makes the block shrink slightly. The more seams in your blocks, the more shrinkage you’ll experience. This can cause real problems when you assemble a bunch of blocks into a quilt top. Leaving a scant seam allowance is most important when you make complicated patterns with lots of seams.To compensate for the shrinkage and make sewn blocks come out exactly the right size, you’ll need to use a seam allowance that is just a hair under a quarter-inch.

1. Use a quarter-inch quilting foot. Most sewing machines today offer a special foot with a built-in guide that helps you sew an exact quarter-inch seam. Not all machines have them. My fancy but finicky Pfaff 2140 has a quarter-inch foot accessory, but the Brother 1500s I now use for almost all my piecing doesn’t have one. So it’s option 2 for me!
2. Create a seam guide on your sewing machine. I find this technique helpful even when I’m sewing with a quarter-inch foot. I can run the guide well out in front of the needle to help me align the fabric as I sew along. To create a guide, you will need a way to mark your sewing machine bed. The ideal seam guide is thick enough to make a little lip that keeps your fabric in place as you feed it into the machine. Some options I’ve seen here and there around the web:

• • Marker line drawn on the machine bed
  • Stack of blue painter’s tape. This is what I use. I stick several strips on top of each other to create a bit of an edge to align my fabric. Here’s the blue tape guide on my sewing machine.

• • Thick foam tape like a Dr. Scholl’s foam bandage
  • Piece of flexible cardboard taped to the machine bed
  • Stack of Post-it notes
  • Thick rubber band fitted around the sewing machine’s free arm (if your sewing machine has a free arm.) Thanks to reader Sue Hamner for this suggestion.
  • A commercially available sewing guide that you can buy at quilt shops or fabric stores. Dritz makes a magnetic seam guide which is supposed to work on any machine. I’ve also seen an adhesive seam guide from Collins that comes with a little measuring device for pinpoint accuracy. I’m leery of using magnets on my electronic machine, so I prefer adhesive to magnetic.
  • A piece of weatherstripping foam. The thickness of the foam creates that little ledge that helps keep your fabric in proper alignment. Use the sticky side against your sewing machine bed. It is easy to remove when needed. Thanks to reader Mary Sloan for this suggestion.

How to Locate Your Seam Guide Accurately

Accuracy is the word here, so you’ll need to do a bit of measuring.

1.  Put a see-through cutting ruler under your sewing machine’s presser foot and lower the needle until it touches a spot just a hair to the right of the quarter-inch mark closest to the right edge of the ruler. (You can also use a piece of graph paper and touch the needle to the first quarter-inch mark on the right side of the paper.)
2. Using the right edge of the ruler or graph paper to align your tape or sewing guide, stick the guide on the machine bed just in front of the feed dogs. You don’t want the guide to interfere with those dogs!
3. Run your fabric along the edge of the guide when you feed pieces under the sewing machine needle.

How to Test Quilt Seam Allowances for Accuracy

No matter what method you use to align your seam, you should check yourself with this quarter inch test.

1. Cut three short, 1½”-wide strips of fabric like this: 
2. Sew the three strips together.
3. Press the seams to the sides, then measure the center strip. It should measure EXACTLY 1”. If it is narrower or wider, adjust your seam guide and retest, then check again.

I decided to test the painter’s tape seam guide I was using on my sewing machine. I sewed the three strips together, pressed them, and measured. On the first try, the center strip measured less than 1 inch. It was TOO SMALL.

I moved the tape a bit closer to the sewing needle and tried again. This time, the center strip was TOO BIG. I had moved the seam guide too close to the needle.

On try #3, I got the center strip JUST RIGHT. Now my seams and my blocks should come out the right size.

The test didn’t take long at all — about ten minutes total. Why did I wait so long to do this? Readers, I challenge you to try this test yourself and let me know how it turns out.