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How to Sew the Perfect Quilting Seam Allowance

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INSIDE: How to Sew the Perfect Quilting Seam Allowance.

When piecing a quilt it is a truth universally acknowledged that all seam allowances must be exactly, precisely, and perfectly one-quarter inch.

Has This Happened to You?

  • Your 12″ x 12″ quilt block measures 11.5″ x 11.5″
  • Seamlines don’t match up on your quilt top.
  • You can never get triangles to sew together correctly.

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How to Sew the Perfect Quilting Seam Allowance

Step 1: The Seam Allowance Problem

Let’s say you follow all of the directions in the quilt pattern to achieve a 12″ x 12″ block. You’ve used a 1/4″ piecing foot and measured the seam allowance to find that it is a perfect 1/4″ from the seam to the raw edge. Once the block is complete it measures 11″ x 11.”

If you’re having trouble with your quilt blocks not turning out in the right size it may have something to do with your seam allowance. Instead of a perfect 1/4″ seam allowance, what you really need is a scant 1/4″ seam allowance.

The first time I heard the term scant 1/4″ I thought, “What! I have a 1/4” foot, what the heck is a scant 1/4″ seam?” Then, I promptly ignored this information and started making quilts using things like an accurate 1/4″ foot and following the seam guide on my machine. Sounds reasonable.

Well, it turns out that I experienced trouble with consistent block sizes because I have a problem on one of my machines. The needle drops slightly further to the left and creates a greater distance between my needle and the edge of my 1/4″ foot. In order to get an accurate scant 1/4″ seam allowance, I would need to know the exact location of a quarter-inch from my needle.

Step 2: What is a Scant 1/4″ Seam Allowance and Why is it so Important?

It turns out that pressing your seam allowance to one side shrinks the seam the width of the top and bottom thread. The more seams in a block, the more shrinkage. The problem continues to develop as you start assembling blocks across a quilt top. Before you know it, the individual quilt blocks have shrunk, affecting the entire quilt top size.

What you need is a seam allowance that allows for this tiny amount of shrinkage. While a thread’s width doesn’t sound like much, it adds up quickly and that is why you need to use a scant 1/4″ seam allowance to create consistent seams so your blocks will line up.

Step 3: It Starts With the Thread

First of all, before we can begin to chat about using a quarter-inch foot (sometimes called a patchwork foot) or achieving a scant 1/4″ seam allowance we first need to discuss thread and why it matters.

If you pop into your local big box sewing and craft store you will have a couple of thread options: Coats & Clark or Gutermann. Both of these brands make great threads for general sewing; however, they are slightly thicker when compared to a finely spun 100% cotton quilting thread such as Aurifil 50 wt.

With quilting, the weight and consistency of thread creates a very slight issue because the thread is taking up a bit of fabric space in the seam. Using a finely spun brand such as Aurifil helps reduce some of the bulk that naturally occurs when piecing.

Combining a finely spun thread with a scant 1/4″ seam ensures that you get perfect 1/4″ seams and no loss of fabric space every time.

Step 4: Creating an Accurate Scant Quarter Inch Seam Allowance

Finding a scant 1/4″ seam allowance is easy. Once you’ve located a scant 1/4″ seam on your machine,  scroll down to find a way to mark this seam allowance using one of the methods below.

  • Place a quilter’s ruler under the presser foot and slowly lower the sewing machine needle until it is a thread’s width to the right of the 1/4″ mark on the ruler. In front of the feed dogs, mark the bed of your machine with one of the methods in Step 5.
  • Or try this method. Using the far-right edge of a piece of 1/4″ graph paper, place the graph paper under the presser foot and slowly lower the needle until it is to the right of the 1/4″ line. In front of the feed dogs, mark the bed of your machine with one of the methods in Step 5.
  • My preferred method is to use a seam gauge (see below) to perfectly line up a scant 1/4″ seam allowance. Place the template under the needle and drop the needle through the tiny hole giving the exact location of a scant 1/4″ seam allowance. Once the location is determined, use one of the methods in Step 5 to create a seam guide. This will assure you get the perfect scant stitch width.

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Below are links to my favorite seam gauges. I use the Ideal Seam Gauge, but the other is equally accurate.

>>>Ideal Seam Gauge

>>>Guidelines 4 Quilting

Step 5: Making a Mark

Now that you know where your scant 1/4″ seam allowance is located, you will need to somehow create a guide.

Below are a few ideas that I have tried with some success.

Make your own seam guide using one of these methods:

  • Use blue painter’s tape and make a stack with 2-3 layers. This will create a guide for the fabric.
  • Use washi tape to create a guide.
  • Mark a line on your sewing machine bed with a fine point Sharpie.
  • Use these Seam Guides because they easily remove and can be used over and over.

Whichever method you choose will work as long as you place the guide in front of the feed dogs. This prevents the seam guide from interfering with the feed dogs when you’re sewing.

Step 6: Testing the Seam Allowance

Now that you’ve created a scant 1/4″ seam allowance on your machine you will need a way to test it.

Use a 5″ square of white fabric and mark a red line down the center. Stitch a 1/4″ seam on one side and a scant 1/4″ on the other to demonstrate the difference. It’s very subtle, but there is definitely a difference.

Both scant and 1/4" seam allowances.

The image below shows an accurate 1/4″ seam allowance. Notice that it is right on the mark. As a result of piecing with this full 1/4″ seam allowance, you could lose a little fabric in the overall block size. For example, on a 12″ block you could lose 1/2″ by not using a scant 1/4″ seam allowance.

Example of a 1/4" seam allowance.

Notice the subtle difference in the scant 1/4″ seam allowance below. As a result, this tiny fragment of space allows for the shrinkage that occurs because of thread width and pressing.

Example of a scant 1/4" seam allowance

If you have a sewing machine with an adjustable needle position, this can be a great way to get a consistent scant 1/4″ seam allowance. Test out several methods to determine what works best for you.

Final Thoughts on How to Sew the Perfect Quilting Seam Allowance

Take the time and determine your best method for achieving the perfect 1/4″ quilting seam allowance. Suddenly you’ll feel confident enough to tackle difficult blocks. And that makes the possibilities endless!

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The Perfect 1/4" Seam Allowance Cover

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