Help with Half Square Triangle Blocks

Posted by Ruth on 3 July 2012 | 0 Comments
This content belongs to Arbee Designs.


I mentioned a second pattern being launched this week in an earlier post, well now it's time to take a look and offer some helpful tips in making it. I'm talking about Cynthia Foster's Desert Blooms. The most obvious pieced section in this quilt is half square triangles so I've put together a few tips for making half square triangles.

What is a half square triangle?  A half square triangle (HST) is a triangle made from a square that is cut through the diagonal. The triangles can be cut as singles but the best and most accurate way is to join two squares together and then cut the diagonal.

Half Square Triangle Block

How to make a Half Square Triangle Block?

Start with two squares of two different fabrics and place them right sides together. Draw a diagonal line through the middle of one square. Draw on the light square so your pencil line shows and is easy to see when sewing.

Now sew 1/4" on both sides of the line. Tip: By making a slightly narrower seam, you will have more room to trim later. This can be helpful especially if your triangle gets out of shape - you have room to get it accurate again.

Sew a less than 1/4" seam on both sides of the line

Cut along the line with scissors or rotary cutter. 

Cut apart

Before pressing the seam to one side, set the bias edge and stitches by pressing it without opening. Now press the seam to one side by placing the darkest fabric on top and using the tip and side of the iron to push it over the seam. This will press the seam toward the dark side.

Press to one side

Place your square ruler on top of your pressed block and align the center diagonal line with the seam line. Make sure the lines for the size you are going to cut, are within the edges of the block. In my case, it's 4 1/2" - you can see the 4 1/2" dotted line just inside the edge of th block. 

Align the diagonal line with seam line

Trim along two sides.

Trim two sides

Turn the block around and align the 4 1/2" square lines with the newly cut edge and trim the last two sides.

Trim remaining two sides

Now you have that perfect half square triangle.

Half Square Triangle

I like this method better than most as it is more accurate. If you cut the squares to size at the beginning, it usually calls for a 7/8" measurement. For example, to get a 4" finished HST, you need to cut a 4 7/8" square to start. No one really wants to deal with those measurements and there is no room for error either. Instead I would cut a 5" square (using the same example) and trim it back once stitched and pressed as I've shown above. 

Thangles are another great way for making HST and especially good if making a lot of HST. This product can be purchased from most quilt shops, however you need to purchase the correct size for what you are making and you don't always have them on hand when you're ready to start.

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