Saturday, August 31, 2013

Foundation Stitching for Half-Square Triangle Units

Using a paper foundation to layer and stitch following guidelines
is the most accurate way to create the square divided in half on the diagonal,
also known as "half-square triangles".
New foundations in three finished square sizes will soon be available
from SnapDragon Snippets through the
Silhouette America online store.

The half-square triangle unit is one of the most versatile there is. There are several methods to create the patch, but using a paper foundation is fast and very accurate. Here are just a few of the blocks that can be created with half-square triangle patches (ignore the oak leaf applique block, please).

Paper foundations are available commercially, but using the Silhouette Cameo (and others) to print and then trim to size means you can make your own foundations at home as you need them.

The three sizes of units available in the print and cut file are shown in the opening image above. These are FINISHED SIZES of 1 1/2", 2" and 2 1/2" squares. The construction steps for any of the sizes is the same. This tutorial will be using the smallest size for illustration.

Step 1. Print and cut your foundation. The 1 1/2" size printed foundation yields 8 units that can then be joined or combined into patchwork blocks and borders. Print the foundations one by one, or see how many you can load onto your regular type weight paper (card stock is NOT recommended).

Cut a "light" strip and an "accent" or colored strip slightly larger than the CUT paper foundation. Then layer as shown: "accent" on the bottom face up, "light" next face together with the accent fabric strip, on top is the foundation, print side up

 With the layers arranged, use straight pins to secure, inserted where the stitching will not be interfered with. 

Step 2. Use neutral thread. Adjust stitching to slightly shorter than regular quilt piecing.

Begin at the arrow head at end corner. Stitch onto the paper exactly on the dashed stitching line. Continue across the first diagonal stitching line to the opposite size of the foundation.

At the end of the first "run", sew off the paper, but leave the thread attached and simply pull a short length of thread through needle and bobbin so the foundation can be realigned to continue stitching the next diagonal. 

Continue on the left of the solid trim line, as before. Sew onto the paper edge, continue EXACTLY on the dashed stitching line, sew across to the opposite cut edge.

Step 3. At the end of the first "run", either pull foundation away from the machine and clip threads, or pull enough thread through as before so that the foundation can be re-oriented to start the second half of the stitching. Begin at the "hollow" arrow head, and proceed as for the first half.

Step 4. After all the stitching has been completed (only on the dashed lines), place the layered section on a rotary cutting mat. 

Lay rotary ruler exactly on the outer solid lines and trim away all layers. Repeat for all four side edges.

Step 5. Position rotary ruler exactly on the perpendicular lines to cut the section into squares. Be exact in aligning ruler and cutting.

Step 6. Position the ruler and cut exactly on the diagonal of the cut squares to divide them into the two triangle halves.

Step 7.  Turn the units over so that the print side is face down on the iron board. Open up and press the "accent" side away from the "light" half.


Step 8. Tear the foundation away along the perforations created by the stitching.

Step 9. Use scissors to trim away the seam allowance end extensions (sometimes called "ears" or "tails"). 

As you can see, this 1 1/2" foundation produces a 2" unit cut edge to cut edge. This size includes a 1/4" seam allowance on each edge, the standard for patchwork piecing.

The units are now ready for piecing into a wonderful patchwork project.

Here are the units aspiring to be in stitched together. Following are a handful more of fun projects that use this unit. Others were featured in a Quilter's Puzzle Box design collection in this tutorial. Find it by clicking here.

 These images were taken from a book project that I was involved with several years ago. Here is a "Thousand Triangles" overall patchwork pattern using a 4" half square triangle size unit, but the pattern would work for any size. 

This miniature churn dash uses the half square triangle patches in a 1" finished size.

Here is the half square triangle blocks sampler that the color and line drawing blocks from the beginning of the tutorial were illustrating.

This block is a pinecone block that is a variation of the bearpaw block.

Hope these foundations give you lots of scope for your patchwork imagination!


  1. Hi Jodi, thank you for having this post. Is there a way to re-size the the foundation piecing in the silhouette software proportionally? Lets say I want larger or smaller.

    1. Yes you can enlarge it using the "lock ratio" box (check it) when enlarging to whatever size you select. The trick with this unit is that you might need to play around with the target size because the seam allowances (1/4" on edges and at diagonal seam) are "built in" and not shown as lines. So you may enlarge the foundation at, say, 125%, then sewn a test unit, and find that the new unit FINISHED/SEWN size is a number that doesn't correspond to the significant measurements a quilter might be used to. If you are seeking a specific new unit size (FINISHED size, that is), you would need to experiment with graph paper, or gridded ruler and pencil to figure out how big the foundation diagram grid would need to be, then do the enlargement or reduction size calculation to figure the percentage of change for the foundation. Formula for enlargement or reduction is: target (new) size divided by original size equals the percentage of change (you have to move the decimal to get it to a percentage kind of product number. Hope this helps.