How to Trim Half Rectangle Triangles
Hello, and welcome to my first MEGMADE Patterns tutorial! This post will walk you through trimming Half Rectangle Triangles like those found in the Matisse mini quilt.
While visually similar to Half Square Triangles, Half Rectangle Triangles (or HRTs) require a little more care when trimming. Because the diagonal seam of an HRT does not produce a 45 degree angle (or two equal angles in the corner of the block), the diagonal seam must be aligned with the corners of the block’s seam allowance, not the corners of the unfinished unit. If you’ve sewn apparel, it’s the same principle used when attaching a sleeve to an armscye—you’re aligning your pieces where the seam will be, not the raw edges of the pieces.
So let’s get into it!
Before we get to trimming, we want to prep our ruler by temporarily marking some helpful guides. This can be done with a permanent marker and later removed with rubbing alcohol.
First, note the trimmed size of the HRT—in this case, 2” x 3½”. It’s helpful to mark this on the ruler with some masking tape or permanent marker.
Next, make a dot in each corner to mark the ¼” seam allowance. For our example, those dots would be at:
¼” x ¼” and 1¾” x 3¼” for the right-leaning HRTs
¼” x 1¾” and ¼” x 3¼” for the left-leaning HRTs.
Begin with your untrimmed HRTs. Here we have right-leaning HRTs on the left, and left-leaning HRTs on the right.
Align diagonal seam with dots on ruler: right-leaning HRT
Slide the ruler up and down the HRT until dots are aligned with the diagonal seam. Make sure that the ruler does not extend beyond the HRT otherwise it might accidentally be cut too small.
Align diagonal seam with dots on ruler: left-leaning HRT
Slide the ruler up and down the HRT until dots are aligned with the diagonal seam. Make sure that the ruler does not extend beyond the HRT otherwise it might accidentally be cut too small.
Trim the top and side of the HRT.
Rotate the HRT 180 degrees, and realign.
Once again align the dots on the ruler with the diagonal seam. The side and bottom that have already been trimmed should also line up with the final unfinished measurement (in this example, 2” x 3½”).
Trim the top and side of the HRT.
Repeat for all of the HRTs
Your trimmed HRTs are now ready to plug into your pattern!
There you have it! With a little preparation, trimming Half Rectangle Triangles becomes just as easy as trimming Half Square Triangles. But if HRTs have you stumped, always feel free to reach out and we’ll troubleshoot together.
Ready to make your own Matisse mini quilt? Get the pattern now with special pay-what-you-will pricing and give my pattern style a try!
