Quarter square triangle blocks can be tricky! Often they are too small...so here are a few tips and hints from my own personal experience which may be helpful.
First decide how large you want your finished quarter square triangle block to be. I wanted 13" finished squares (13 1/2" unfinished).
So I cut 15" squares from four different fabrics. this will be enough to make four quarter square triangles. If you follow the strict formula you would cut smaller squares at this, but I prefer to work with a bit of a safety margin, allowing for the fact that I might sew with too large a seam allowance or heaven forbid a seam that's not quite straight. This gives me some breathing room and makes the whole process much less stressful!
On two of the squares you need to draw some diagonal lines - usually you pair fabrics up with one light fabric and one dark fabric - so choose the lighter square to draw your lines on.
You need to draw a line from one corner to the corner diagonally opposite. This is your cutting line. Then you want to draw a line 1/4" either side of this line which will be your stitching lines.
I sometimes do this as shown below. I lie the fabric on my mat with the tips touching one of the vertical lines. I usually check that the horizontal as well as vertical corners are in line with one of the lines on the mat.
Then I use the 1/4" marking on the mat to the right of the original line and move my ruler accross to this. I check the ruler is aligned with the 1/4" marking at both the top and bottom of the mat and then draw my line in pencil.
Then I use the 1/4" marking to the left of the original diagonal line and draw another line.
See the picture below where I am about to draw the line to the left of the original diagonal.
Then sew on the stitching lines. I do this with trying to sew slightly inside the line (towards the centre) to make my resulting square as big as possible. Oh, and pinning helps too!
Once you've sewn on both stitching lines, cut on the original diagonal. Then open and press (with seam towards the dark side). Now you should have two half square triangle units - pair A.
Repeat the whole process with your remaining two whole squares to get another two half square triangle units - pair B.
Next take one pair A square and draw lines on it as you did in the first few steps. This time your lines go on the opposite diagonal.
Pair this up with the other unit right sides together. Make sure you have them the right way around. The corners, edges and seams should be aligned, but the light fabric of pair A should be on top of the dark fabric of pair B. I normally just fold back the edge to check.
Next step is to sew along the drawn lines - but I have a hint here. The thing I care about most is getting a nice intersection where all fabrics meet. rather than sewing the whole seam and then the other one and hoping that they meet perfectly, I just sew about a 1" long seam on the drawn line over the intersection first. Then I check the join. If it's OK I do another 1" long seam on the other drawn line and check it. If they're both ok I do the full seams on the drawn lines - but if not I rip it out and start again until I'm happy. I normally have to pull a seam apart about 50% of the time - so if you feel like this happens a lot to you, you're not alone! It's worth it for the end result and because I only sew an inch it doesn't take long to sew or rip apart. See pic below (a bit blurry but you can see that I start just above the intersection and go about the same distance past it.)
So once you've sewn both seams you cut and press as before.
Next comes the squaring up. I use a large 15" ruler. Kind of hard to describe it but here's what I do.
I position the ruler so the 1-1 is at thetop right hand corner.
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Follow the diagonal down and make sure that the 6 3/4" marker is at the central intersection of the block. (6 3/4" is half of 13 1/2")
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The 13 1/2" mark at the bottom left of the same diagonal should still be aligned with the seam
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I then look at the 13 1/2" mark at the top left of the square which should intersect the seam
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Then I look at the 13 1/2" mark at the bottom right of the square which again should intersect the seam.
In the picture above all the pointers are great except the bottom left hand corner (this shouldn't happen to you as I think I had used a 14 1/2" original square for this one)
If all these points are in the right place then this is perfect and you should cut your square. as I'm right handed I leave the ruler in the exact spot and cut the right hand side and top. Then I rotate the block so that the good top right corner is at the bottom left. I then line up the 13 1/2" mark with this bottom corner - check all the other pointers as before and then cut again on the remaining two sides.
If all the points aren't in the right place, then you have to work out what to do. Last resort is to re- sew which probably won't work any better. If you can work out a position that is a good compromise. Sometimes if three corners are good and one isn't I'll leave it like that and make sure the dud corner is on the outside of the quilt, rather than in the quilt centre.
In the pattern for the bluebird of hope quilt I sew 16 of these units, choose the best 13 to use and make sure that the ones that are perfect are in the centre of the quilt. (No one looks too closely at the edges)...
Have fun - if you have any other tips please add them in the comment below.
