The title of this post should be 'life happens.'
My intention was to talk about accurate 1/4" seams and then my adult son was in a go-cart accident and shattered his left arm. Needless to say, I have not had time to write a 'new' tutorial, so here is a substitute one.
First, I oversize my half-square triange units and use Eleanor Burns Square Up Ruler to custom cut them to size.
Here is a you tube video on Eleanor Burns Square Up Ruler:
Just copy and paste the link into your brownser.
Once you have 4 hsts made and squared up,
lay them out as shown above.
Fold the right HST units over the left ones, RST.
Sew the units together starting at the edge where the diagonal seams align. I call this a critical point. I always put the critical points into the machine first. This may require you to flip the units over so that diagonal seam intersection goes into the machine first. If you do this, you will have better control over that 1/4" seam. If the diagonal seam goes through the machine last, the material will have moved from the action of the feed-dogs. Try it both ways to see the difference in the results.
Once you have the two pairs sewn together, align them as shown.
The unsewn edge of the left one is on the top and the unsewn edge of the right one is on the bottom. Look closely to see the stitches of the seam.
Finger press the left seam allowance down and the right seam allowance up.
When you fold the right unit over the left unit, RST, the seam allowances will be opposed. Note that the one on top is pressed up or away from you. This will help the seams to lock together when sewing the units together.
Align the bottom edges and pin in place. Now sew the seam.
Collapse the seam intersection as seen. Note that some seam allowances are pressed to the light. If you are worried about the red showing through, you can trim just the red seam allowance down to an 1/8th inch. When you flip this unit over, the seams will be perfectly aligned as long as each hst was exactly the same size. We will discuss grid dimension at a later date.
For more info on collapsing seams, go here.