Half Rectangle Triangles {A Tutorial}

One of the blocks this month for the Make It Modern Bee is a diamond made with half rectangle triangles.  The tutorial was from a reputable national quilting site, but it did not work.  I tried it twice, and then noticed at the bottom of the comments other people had expressed that they too ran into the same trouble as me, namely there was too much seam allowance at the skinny points and almost no seam allowance at the fatter points. 

After thinking it through, that outcome made sense.  With half square triangles, the angles are 45 degrees, even on both sides of the seam.  But with these rectangles, it looks like the angles are even, but they are not…one is more acute and one is more obtuse, so that’s what causes the variance in the seam allowance.

The solution is pretty easy.  The diamonds have to be sewn together in a specific order, and some of the seam allowances need to be 3/8” to 1/2”.  Here’s how I did it.

***This tutorial yields two diamonds that each measure approximately 8 1/2” x 12”.

Cut four rectangles from your diamond fabric  and four from your background fabric that measure 5 1/2” x 7.5”.  This is a little bigger than the sizes in the original tutorial.  I found that my rectangles weren’t quite big enough to square up (or rectangle up!) perfectly, so I just increased the size a half inch.  After making the block a few more times, I do think the raw sizes need to be an entire inch bigger than your finished size.

Now, mark the back of your background fabric with a diagonal line for sewing.  You can either mark one diagonal and sew a 1/4” on either side of it or you can mark the two sewing lines on either side of the diagonal as I did.

It is important to draw two diagonals going one direction and two diagonals going the other direction.

Now this part is the same as the original tutorial.  Line up one of your background rectangles across one of your diamond rectangles.  Match up the corners and pin in place.  Then, either sew a 1/4 inch to either side of the diagonal you drew, or sew on the 1/4 inch lines you drew.

Cut down the center of the two seams and I am a seams-pressed-open kind of gal, so I pressed them open.

Here is the trickiest part of the process.  You now need to “square up” your rectangles.  It sounds a little confusing, but is pretty easy.   Just align the corners of your ruler so that the 4 1/2 inch marker is in one corner, and the 6 1/2 marker is in the opposite corner.  Make sure you have enough fabric around your ruler and on the other sides to cut off some excess.

Once all four of your rectangles are trimmed, lay them in a diamond formation.  Sew the top two triangles together with a 1/4” seam allowance.  Sew the bottom two triangles together with a 1/4” seam allowance.

Then sew the top and bottom pieces together using a 3/8” seam allowance.  You may want to use up to a 1/2” seam allowance if you use “scant” 1/4” seams.   I’m kind of making this up, but I think the size of your 1/4 inch seam is inversely proportionate to the side seam allowances.  So, if you are like me and sew with a scant 1/4”, you’ll need to use a 1/2” seam allowance to sew the top and bottom together.

I press my seams open.  You can see how much bigger the horizontal seam allowance is compared to the vertical seam allowance.

I trimmed each side down to a 1/4” seam allowance and my block finished up at 8 1/2” x 12”.  

Now the original tutorial said this would work with any size rectangles.  I wish I could come up with some kind of size chart but my math capability isn’t that good!  (I have a degree in English, so go easy on me!)   But, I am pretty sure you just need to add 1/4 inch  to the length of each of your rectangles if you have a finished size in mind.

This is a fast way to make diamonds with little fuss.  Hope you found this helpful if you ever want to make Half Rectangle Triangles!