The Triangle in a Square quilt block (aka 'Peaky and Spike') is most often used as a unit in other blocks, like the 54-40 or Fight quilt block.
Paper piecing is a reliably accurate method of creating this useful triangle unit and is shared below.
You will also find free downloads for 2", 3" and 4" finished paper piecing patterns.
Because this is one of those 'basic units', there are plenty of pictures to step you through the process.
If you're a more experienced quilter, the cutting instructions and downloadable patterns are probably more than enough.
Two contrasting fabrics are needed to make this Triangle in a Square quilt block. Our Fabric 1 is yellow; 2 is orange.
Choose the finished size and cut as instructed below.
Cutting Chart for a~Paperpiecing ~
|Finished Block Size
|3" x 2¾"
|4" x 3¾"
|5" x 4¾"
|2½" x 3"
|3" x 4"
|3½" x 5"
|Unfinished Block Size
Position Template A on top of the Fabric #1 rectangle and cut out the shape. The top and bottom of the template should be even with the top and bottom cut edges.
Layer the Fabric #2 rectangles right sides together before cutting.
Lay Template B on top aligning all the edges.
With your rotary cutter and ruler cut through the template and all the fabric layers along the solid diagonal line. After cutting there are four skinny, outside triangles—2 for the right side and 2 for the left.
You need only one of each per block. However, this method ensures that you will have a left and a right patch.
After subcutting a pair of rectangles, these are the resulting patches. You'll need just two for a single block.
If you have a difficult time 'eyeballing' the 1/4" seam allowance, then mark it on the paper pattern as shown below. (That line is drawn with a red Micron pen but you can use pencil, too.)
You can also see that the pattern has been rough cut just past the dotted line that marks the edge of the final unfinished block.
Position a skinny triangle, right sides together with the center triangle, aligning the long edges. (It doesn't matter which side you do first.)
The heavy black line (above) is where the seam line is on the printed side that we can't see. The orange patch is positioned with approximately 1/2" extending past this seam line at both ends.
Flip the Triangle in a Square quilt block pattern over to the printed side and stitch with a short stitch length (1.5mm) on the line between the two triangles.
Start and stop your stitching a good 1/4" before the beginning and after end of the solid line and past the outside edges (dashed square) of the block.
When this unit is pieced into your quilt, a line of stitching will cross these seams and secure them. There is no need to backstitch.
Press the unit as it was sewn to set the seam.
Now open the skinny triangle patch so the pretty side shows and press again. Be careful not to press a tuck in at this seam allowance.
To complete the sewing, repeat all of these steps for the remaining skinny triangle, stitching and pressing as before. It will look like this.
At this point, I hadn't bothered to trim the thread tails or dog ears.
There's no need to take the time during piecing, because the final trim takes care of it. (I like to be economical with my efforts. There's never enough time to make all the quilts in my head.)
To complete the unit, align the 1/4" line of your ruler with the solid black line on the outside of your block. Trim. Repeat for the three remaining sides.
After trimming your triangle in a square quilt block this is what you've got!
On the bottom edge, the orange fabric doesn't intersect the corner.
That's OK. It's not a mistake.
It is exactly as it should be due to the angle of the sides.
Now remove the paper and...