Quarter Square Triangles | Top Tips

If you are a long-time reader of my blog then you’ll already know that I love half square triangles and that they are my favourite patchwork “feature” it use in a project. This love also extends to quarter square triangles which are essential two HSTs combined to create two new units. For me there’s nothing better than a perfectly trimmed square-triangle in a patchwork project…but what if they aren’t perfectly trimmed? Does that really matter? Can you wing it and make do with inaccurately cut HSTs and QSTs? Read on and see what you think…

Trimming HSTs

Half square triangles only have one seam which makes them super easy to trim accurately. To trim a HST you need to use the 45o diagonal line on a quilting ruler. If your ruler doesn’t have one then I’d highly recommend adding one with washi tape…check out my Washi Tape + Sewing blog post for more info. Line up the diagonal line with the HST seam and trim the two exposed sides. Then turn your HST, match the 45o line with the seam again and trim the remaining two sides.

The examples below are being trimmed to 4.5″. On both examples I have the 45o line lined up with the seam however with ruler position on the light blue I’ll be trimming a lot from two sides and a very small amount from the other two, but on the dark blue the ruler position will mean I trim roughly the same amount of fabric off all four sides.

So what difference do these two ruler positions make to how the trimmed HST looks? The photo below shows that it makes no difference at all.
One thing I would be wary of when trimming HSTs if how evenly they have been pressed. If you aren’t careful, it can be easy to mis-shape a HST when it is pressed and an even trim round all four sides is a simple way to help sort this out.

HST trimming methods compared

Trimming QSTs

Quarter square triangles have two seams. This doesn’t make them difficult to trim accurately but you do need to take a little more time. To trim a QST you need to use the 45o diagonal line AND the markings on the edge of the ruler.

The examples below are being trimmed to 3.5″.

The first example has the 45o diagonal line lined up with one of the diagonal seams but it hasn’t taken into account where the 3.5″ markings on the ruler are matching up (or not!) to the other diagonal seam. Trimming like this has resulted in one diagonal seam running perfectly from corner to opposite corner but the other seam is not lining up to the corners; this has caused the four triangles to be uneven and this issue will only get worse once this little block is sewn to another.

The second example has the 45o diagonal line lined up with one of the diagonal seams and also has the 3.5″ markings on the ruler matched up to the other diagonal seam. It is really important that markings for the size of QST you want to trim down to are both right on the diagonal seam. Trimming like this has resulted in both diagonal seams running perfectly from corner to opposite corner.


Summer Braids pattern help

My patchwork quilt pattern Summer Braids has a lot of HSTs and HS-QSTs (half square-quarter square triangles…basically a blend of a half square triangle block and a quarter square triangle block).

The all-over twisted braid design of this quilt is more effective if all the seams are lined up well and this is so much easier to achieve if the trimming of the HS-QSTs has been done accurately.

Trimming the HS-QSTs is done in exactly the same way as I have shown above with the QSTs.


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