Test Your Seam Allowance

Why test?

For piecing success, the biggest contributing factor by far is accuracy in cutting and sewing. Small errors become magnified if a block involves many different pieces. In the worse case scenario, blocks can end up seriously mismatched in size and this makes the job of assembling a quilt top very difficult.

Cutting Accurately

Pressing fabric first is essential so it will lie smoothly on your cutting board. Use a quilter’s ruler and a rotary cutter to get a nice, crisp cut. After a couple of cutting disasters, (beautiful teal spot fabric, I still remember you!), I always follow the rule, ‘Measure twice, cut once!’

1/4″ Sewing Feet

Sewing with an exact 1/4″ seam allowance takes a little practice. Many machines come up with a 1/4″ foot. If one does not come as standard with your machine, these feet are generally a worthwhile purchase. Here is the foot which comes with my Pfaff machine. Different feet are designed to be used in slightly different ways. Always read the instructions that come with your machine to understand how to operate your 1/4″ foot correctly.

Once you have got familiar with using your machine’s foot, I would recommend that you sew a quick test block to measure the accuracy of your seam allowance.

Testing Your Seam Allowance

To begin, cut 3 2″ squares. I only use little squares that I can cut out of scraps. I do love my stash, even the scraps!

Pin one side square to your central square. With my machine, I carefully align the raw edge of the fabric with the edge of my 1/4″ sewing foot. Usually you will need to sew a scant 1/4″ seam for the finished seam allowance to come out as 1/4″ so don’t check your accuracy by measuring the finished seam allowance, it may give you misleading results. Pressing the pieces uses up a small amount of fabric and that’s why the seam is usually just slightly under the 1/4″.

Pressing Seams

Once I have stitched the seam, I press the seam as it has just been sewn. This is to sink the stitches into the fabric.

Now press your seam towards the darker fabric as shown below. As you can see the fold in the fabric takes up a little room.

Adding the Second Square

Adding another square makes the test more accurate as two seams will reveal a larger discrepancy in size than just one seam.

Join the third square to the other side of the central block. Press as before and you should have a little pieced block like that shown below.

Measuring Your Work

Now measure the width of the central square by placing your ruler on top of the pieced block, carefully aligning the edges. The main square should measure exactly 1 1/2″.

Align the left-hand edge of the block with the ruler and confirm that the width of the entire pieced unit is exactly 5″.

Adjustments

If your block is too large then you need to increase your seam allowance. If its too small then you need to reduce your seam allowance. When you are making complicated pieced projects, even a small error in the seam allowance can have a significant impact on the finished block so it is well worth taking the time to confirm that your seams are spot on.

Have you ever had any quilting disasters? And if so, were you able to salvage your project? I’d love to hear your stories!

If you find this tutorial useful, check out my applique tutorial.

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