QST (Quarter Square Triangle)
An Exercise in Squaring Up
So you want to make a perfect Quarter Square Triangle? The key is squaring up. If you don’t know how to make an HST (Half Square Triangle), don’t start this exercise. Go to our HST tutorial and become familiar with this technique first. Then come on back and learn to make QSTs. If you’re already comfortable with HSTs and squaring up in general, then you’re probably ready to master this assembly.
To make a QST in two colors cut one square of each fabric, making them 1″ larger than you want your completed QST to be. I want a 4″ (unfinished) completed QST, so I’ll start with two 5″ squares of fabric. This will generate two QSTs.
Cut your initial squares as close to square as you can. This will save you some effort in the squaring up process at the end.
Draw a line on the back of your palest square from one corner to it’s diagonally opposite corner. Rotate the square 90 degrees and draw the other diagonal.
These lines are guides, not seam lines. When both lines are drawn there should be an X across your pale square.
Line the first guide up with a scant 1/4″ seam on your sewing machine and sew the entire length. Turn the block 180 degrees and sew down the other side of the guide also at a scant 1/4″.
Lay the block out on your cutting mat and cut down the guide line, then rotate the entire mat (without moving the block) so you can also cut down the other guide line.
Press the four triangles you’ve just made with the seam allowance falling towards the darker fabric. Notice that you’ve made two kinds of triangle pairs. One pair has dark on the left, one pair has dark on the right. When these are sewn together, they will be identical, but make sure that you know which two triangle pairs you’re sewing together in the following steps to prevent coming up with a color combination you didn’t want!
Lay out one of the four triangle pairs on the cutting mat and line up the seam with a horizontal line on your grid ruler. Make sure that the long edge of your ruler is as close as you can get it to the long edge of the triangle pair without losing part of the edge under the ruler. Cut off any excess on the long edge. This is a very important step. You have just squared up the triangle pair. This keeps your join in the center of your finished QST absolutely square. Repeat with the other three triangle pairs.
Pick the two triangle pairs that you want to compose your QST with. Put them together, right sides facing eachother. Sew 1/4″ seam down the long edge. Press open. Check for square by putting the QST on your cutting mat and lining up a horizontal and vertical line of your ruler on the center of your QST. If they don’t line up nicely, you probably didn’t quite square up the triangle pairs or you are pulling a bit as you sew the two triangle pairs together, causing some distortion along the bias.
Lay the QST out on your cutting mat. Don’t be surprised if it looks pretty darned Un-Square. That’s why we made it bigger than we want it. Line up a 45 degree line with one diagonal on your QST. Scoot your ruler as close to the edges of your QST as you can without losing any of the edge under the ruler. Trim off all excess.
Twist the QST around 90 degrees (so a different color is on the right). Line the diagonal back up as before, but this time line the measurement on your ruler that corresponds to half your desired completed block size up with the center of the X formed by the intersecting seam lines on your QST. Trim off all excess fabric on the two edges exposed.
Turn the QST once more, but this time turn it 180 degrees. Line the diagonal back up and line the center measurement back up. Trim away any excess.
That’s it! Now you have one perfect QST!