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What exactly is a "scant" seam allowance and do I need to worry about it?

• Jinny, I’m working on a pre-cut block of the month quilt and the instructions call for a scant 1/4 inch seam allowance. If I hand piece rather than machine, do I need to worry about the "scant" part? If I do need to worry about it, how do I achieve it?
  
  Submitted by
  Sheila
  Spring, TX
  

Jinny's Answer

• Consistent, accurate seam allowances – whether by sewn by hand or machine -- is one of the keys to creating quilt blocks in which all the pieces fit together nicely and quilt tops that lay nice and flat.
  
  A ¼-inch seam allowance is standard in quiltmaking, but sometimes patterns call for a “scant” ¼-inch seam allowance.  A scant seam allowance means one that is just a little smaller than ¼-inch. Why use a scant seam allowance? There are several reasons:

  1. Sometimes a patch can’t be accurately cut using a rotary cutter and standard quilter’s rulers, so the pattern maker determines that you need to take a slightly smaller seam allowance than usual.
     
     Here’s an example:  Let’s say that you were going to make a 9-patch block that finishes 8" square.  Each patch finishes 2 2/3".  When you add ¼" seam allowance to all sides, the patch would need to be cut 3.16" inches;  that’s just a bit bigger than 3 1/8" (3.125") and a smidge smaller than 3 3/16" (3.1875"). Since most patterns work in 1/8-inch measurements, you might be instructed to cut the patches 3 1/8" square and use a scant seam allowance so that your block will finish closer to the actual size.
     
     
     
     Small differences add up, especially when piecing strip-sets or blocks with many seams. This is one of the reasons I like to use templates:  templates can be made in any size so they are often more accurate.
      
  2. Many machine sewers use the edge of their presser foot or a line on the throat plate to guide their seams.  You may be surprised to learn that using these guides may be less accurate than you think.  In addition, most hand-sewers don’t mark the sewing line on their patches; they mark the cutting line and then “eye-ball” the seam allowance.
     
     To test how accurate your seam allowance is, try the following: stack three small pieces of fabric and use your rotary cutter and ruler to cut them exactly 1 ½" x 4". Now sew the three pieces together along the 4" seam using your usual seam allowance and press them as you usually do.  The overall patch should measure exactly 3.5" x 4" and the center patch should be exactly 1" wide.  If either of these measurements isn’t accurate, you may need to adjust your sewing methods. I suggest you try marking the corners of your patches at exactly the 1/4" mark; that gives you a starting point and a point to aim for when stitching.  My Perfect Piecer is designed for exactly this purpose.
     
     
      
  3. The thread you use takes up seam allowance, too.  Use a fine, good-quality thread for your machine sewing; my staff prefers Aurifil’s 50-wt thread for machine sewing.  Because hand-sewing is a running stitch, there is less thread in the seam. A somewhat heavier thread is usually used for hand-sewing; my favorite hand-sewing thread is Aurifil’s 28-wt.
      
  4. Pressing makes a huge difference in the finished size of a block.  At one time or another, most of us have found ourselves steaming a block to make it lie flat or get it to the correct finished size. So we know that pressing, particularly with steam, can stretch a block.
     
     In addition, most quilters today press seams to one side. Shop Manager Barb Hollinger tested this recently and found that blocks with seams pressed to one side are usually a little smaller than those with seams pressed open. Hand-sewn blocks need the security of a seam pressed to one side, but machine sewers should determine what works best for them.

  So Sheila, if a pattern tells you that you need to use a “scant” seam allowance, the patches/blocks probably need to finish just a little bit bigger than they would if you used a standard ¼-inch seam allowance.  If you’re hand-sewing, you might want to mark a few spots on the ¼" seam line and then sew your seam just a smidge closer to the edge of the patches. Machine sewers can try changing the needle position on their sewing machine if they have that feature, or scoot their patches a little further to the left of their presser foot than they usually do.
  
  Good luck!  Let us know how it goes.