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Testing Your Scant Quarter-Inch Seam

Testing Your Scant Quarter-Inch Seam

By Janelle Cahoon, Quiltcentric

Quilt patterns are written for a quarter-inch seam, but when you open and press your sewn unit a thread or two width of fabric is lost in the turn of the seam.  For the finished size of the unit to be accurate, it’s important to sew a “scant” quarter-inch seam, one with just a thread or two less than a true quarter-inch wide seam allowance.

A lot of people say accuracy isn’t really that important for piecing – and for some patterns they’re right.  But for a complex block with units that build on one another, those tiny inaccuracies in the seam allowance could mean that the outer pieces of the block don’t fit at all!

The standard way to test whether your seam allowance is actually a scant quarter inch is this:

  • Cut 3 pieces of fabric 1½ “ wide by 5 inches long.
  • Mark your normal seam allowance on the throat plate of your machine with a piece of masking tape.
  • Sew the 3 pieces of fabric together side-by-side using your masking tape marking as a guide.
  • Press open and measure the block.
  • The width of the block should be 3½” exactly.
  • If the measurement is off, cut 3 more strips, adjust the placement of your masking tape guide and sew again.
  • Repeat until your sewn block measures the correct width. 

Finally, mark the proper place on the throat plate of your machine with several layers of masking tape to make a little curb to help keep your fabric in line as you sew.


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