Cutting your fabric to achieve accurate ¼ inch seams

One of the common problems all quilters have is achieving an accurate ¼ inch seam allowance. Using the ¼ inch piecing foot or a ¼ inch mark on our sewing machines is not enough. Depending upon the thickness of our fabric and thread, folding the seam over “takes up” a little width. Most of us try to compensate by sewing a “scant” 1/4 inch seam.

Of course it also depends upon how many seams are going to exist in a block. For a simple block like a four patch, there is only one seam in each direction so it doesn’t matter so much if the seam takes up a little extra. But for blocks with many seams, it can be a major problem.

Here’s an alternate approach: cut the strips or pieces in your quilt slightly larger. And I do mean slightly. You can use the lines on your rulers to do this.

Here is an example. I am using an old ruler I own manufactured by Quilter’s Rule. It has rather wide lines. For newer rulers with narrow lines, you will have to develop your own method and run tests to figure out the amount of adjustment needed.

For the purposes of this test, I cut six 1 ½ inch wide strips, each about 6 inches long. First, I cut them aligning the fabric edge with the middle of the 1 ½ inch line, as shown in this photo.  Ignore the fact that the ruler line shown is the 1 inch line; I took the photos after completing the test and placed the wrong line on the fabric edge.  Just pretend it is the 1 1/2 inch line!

Cutting with half of the line thickness

Cutting with half of the line thickness

I then sewed these six strips together using my ¼ inch presser foot and being careful to sew accurate seams. Afterward I pressed the seams carefully, using “Best Press” to get the “block” nice and flat. The resulting block is shown below. The extra fabric taken up in the five seams results in a block that is too small – 6 ¼ inches instead of 6 ½.

Finished test block using half the line thickness is too small

Finished test block using half the line thickness is too small

The second test was done aligning the fabric with the left edge of the line, shown here.

Cutting using all of the line thickness

Cutting using all of the line thickness

Again the six strips were cut and sewn together. Now the block is 6 5/8 inches, slightly oversized. But it can easily be cut down to 6 ½ inches if needed.

Finished test block using all the line thickness produces a big enough block

Finished test block using all the line thickness produces a big enough block

I have also done this test with a newer “thin line” ruler and learned to judge where to line up the fabric edge to make the strips slightly wider.

I really like the idea of solving this size problem in the cutting of the strips, rather than trying to solve it later in the sewing. I am going to try to make it a habit in the future, especially when constructing pieced blocks with many seams. Maybe you will find this a useful tip also.

2 thoughts on “Cutting your fabric to achieve accurate ¼ inch seams

  1. Melanie McNeil

    There are a lot of different variables that add into the finished size of the block. As you mention, the heft of the fabric, the thickness of the thread, and how carefully you press the finished block all affect it. But there’s more than that. I’ve seen a lot of blog posts with photos that imply the quilters don’t press carefully BEFORE cutting. All the little ripples and wrinkles do affect the accuracy of cutting. And how you press is important. I often press my seams open, and sometimes it is specifically to adjust the sizing. Also you’re right, just using a 1/4″ foot doesn’t solve the whole problem. I know that for my foot, I need to be about a thread away from the guide. Someone else’s machine/foot might require the fabric to be just touching it. Also when you sew triangles, there is a different adjustment needed because of the rounding error of the sizes we cut.

    If you regularly oversize your cuts, assuming you’ll trim your blocks, that works fine if you’re never sewing triangles. But if you end up with oversized variable stars, for instance, and trim them, you can lose the star points.

    I’ve worked at improving my accuracy for many years and am pretty good. When I get a pieced border on a medallion quilt, usually my whole length is very close to what it should be, less than a quarter inch different (and that is a fudgeable amount over a long quilt edge.) The BEST tip I can give is to make a block (or parts of a block) and measure right away. Make adjustments in your seam allowance right away. Do it multiple times if you’re coming and going from your work over time. Then when you assemble your blocks (or other parts) measure again. Sew two blocks together, press, and measure. If you’ve oversized it, you can adjust the next seam allowance to compensate.

    Good luck in finding methods that consistently work for you. I still play with it, still find errors, still rip seams, and still improve.

    Reply

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