Making QST from HST

 A QST unit is a quarter-square-triangle square, a square made up of 4 triangles.

Traditionally, it's made with 4 individually cut triangles, each triangle one quarter of a square, with the straight grain of fabric on the long side of each triangle.  This involves sewing on the bias, which can invite stretching and distortion.

In this tutorial I'll share how to make QST without cutting individual triangles or sewing bias edges.

Let's agree on a couple of definitions before we start.  

• The finished size of a unit is the size of a unit after it is sewn to other parts of the quilt, with the seam allowances taken in by the seams.
• The unfinished size includes 1/4" extra on all sides for seam allowances.

 For example, an unfinished 4 1/2" unit will be 4" finished in the quilt.

Please note that I prefer to make units a touch oversized then trim down to exact size and perfect shape.  This is more forgiving of slight variations in sewing.  The measurements I share will reflect that.

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HOW TO MAKE QST UNITS

Step 1.  Choose four fabric squares, each 1.5" larger than the desired finished QST size.  This is enough to make four QST units.

Step 2.  Referring to this tutorial and the notes below make 2 HST, trimming them to 1" larger than the desired finished QST size. 

• Refer to the diagram below to see how to distribute the 4 fabrics between the HST to get the desired fabric distribution in the final QST.

• The four squares you started with will yield two HST1 and two HST2.  You'll use one of each to make one pair of matching QST.

• Press either towards Fabric 1 in HST1 and towards Fabric 4 in HST2, OR away from Fabric 1 and away from Fabric 4

These are the two HST I will be working with.

Step 3:  Draw a line, diagonally from corner to corner and perpendicular to the seam line, across the back of one HST.   This will be a guide for sewing in step 5.

• If you do not have an accurate 1/4" guide on your sewing machine or presser foot, you may prefer to draw guide lines on either side of the diagonal, 1/4" away from the diagonal, as I do below.

Step 4:  Layer HST1 over HST2, right sides together and with seam allowances in opposite directions.  

If you have pressed in the directions specified in Step 2, the fabrics should fall in the right order.  You can check by folding HST1 back lightly along the drawn line to preview the QST.  

Step 5:  Making sure the seams are butted up tightly next to each other, sew 1/4" on each side of the diagonal, across the existing seams.

Step 6:  Cut between the sewn lines to separate into two units.

Step 7:  As you press a unit open, spin the seam allowance to reduce bulk in the center.  The second half of this tutorial explains how to spin seams.  Alternatively, press seams open or to one side.

Step 8:  Carefully trim the QST unit 1/2" larger than the desired finished size, keeping all the seams intersecting the corners of the unit.

• Position the rotary cutting ruler over the unit, shifting the ruler as needed until the markings for the size you need intersect seams in all three corners and the a corner of the ruler intersects the last corner of the unit.  

• The  example below shows trimming to a 4" square.  The points circles in red highlight the measurements. Please note that I have exaggerated the amount of fabric to trim away in the example below so that you can see the intersection points more clearly.  Using the measurements in this tutorial, you would need to trim away less than 1/8" on any side.

• A:  The diagonal seam bisects the corner of the ruler.
• B:  The 4" mark along the top edge of the ruler meets the diagonal seam.
• C:  The horizontal and vertical 4" measurements lines intersect over the diagonal seam.
• D:  The 4" mark down the side of the ruler meets the diagonal seam.

Step 8:  Trim away the excess fabric at the top and right side.

Step 10:  Turn the unit 180 degrees and position the ruler so the required measurements are flush with the two sides you trimmed in the last step.  In this example, the 4" vertical and horizontal measurements are flush with the previously trimmed  edges.

Step 11:  Trim the excess fabric at the top and side.

The QST unit is now complete.  Remember, it includes 1/4" seam allowance on all sides, so it will be 1/2" smaller once it is sewn into the quilt.

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For quick reference, here's a summary of relevant measurements:

• Starting squares:  finished QST size + 1.5"
• HST trimmed size:  finished QST size + 1"
• QST trimmed size:  finished QST size + 0.5"

For example, for a 4" finished QST:

• Starting squares: 4" + 1.5" = 5.5"
• Trim HST to: 4" + 1" = 5"
• Trim QST to: 4" + 0.5" = 4.5"

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I hope you have found this useful.  Please share in the comments if you have any tips and tricks for making QST.

Happy quilting,

Joanne