Nifty Notions: When is a ¼ inch not a ¼ inch?
A comparison of using scant quarter inch versus quarter inch seam allowance for patchwork by Judy Hall, a regular contributor to Into Craft.
Last month I mentioned sewing a scant ¼” seam for patchwork as opposed to a ¼” seam allowance. It has always raised so many queries as to why it is necessary and I certainly received emails privately asking for more information.
I am constantly being told by students, “But I do sew with a quarter inch foot and I do sew fairly consistent seams”. Patterns DO say to use a ¼” seam but what they are really meaning is to sew using a scant ¼” seam if machine piecing. – Why? – To achieve perfect matching of pieces and blocks.
So why do we need to sew with a scant ¼” and what is a scant ¼” seam? When sewing by machine, the nature of the top and bottom threads locking to form a straight row of stitching takes a little more space than the traditional hand stitch method. Also, seams are not pressed open as we do for dressmaking seams; they are pressed to one side so as to prevent the batting from ‘bearding’ through a sewn seam. This extra tiny fold of fabric takes up the difference between a ¼” seam and a scant ¼” seam. Only two threads worth, but this makes a huge overall difference. Hence, if piecing by machine, you should always use a scant ¼” seam allowance.
The yellow thread shows a ¼” seam and the white thread shows a scant ¼” seam.
Even if you are using a Patchwork Foot or Quilting Foot, you should CHECK your seam allowance stitching line. Make adjustments if necessary to be perfect. There are several methods and tools to assist and you should refer back to last month’s editorial for some firm favourite tools to assist. Go to Nifty Notions: Sewing Straight
But first let’s run a test on your machine.
Cut two 2 ½” squares and one rectangle 2 ½” x 4 ½”.
Sew the two squares together the way you would normally sew your patchwork shapes together. The sewn piece SHOULD measure the same as the rectangle. Does it?
Here is a basic block sewn with a ¼” seam and the same block sewn with a scant ¼”. I think you can easily see that cross sections are just not going to match up with the ¼” seam.
Note the pressing of the sections and the spiralling of the centre seam.
Note in the right hand side block, sewn with ¼” seams, the points don’t precisely match and the side edges are irregular.
How did your test pieces measure up?… Is adjustment needed?
All better than the elastic band around the freearm of your machine, sticky tape or using texta or nail polish to mark the guideline!…Hmmm.
Off to the sewing room to sew some patchwork blocks with everything perfectly aligned up like you’ve never sewn before because you are now sewing with a scant ¼” seam!
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