How to PreTrim Triangle Points, Using the PrepTool
The Lip Edges on the PrepTool Catch the Fabric's Edge,
Making it Easy to Accurately Line Up & PreTrim Points.
If you've worked with Triangles at all, you have definitely trimmed off a few Dog Ears, Bunny Ears or Triangle Points which all mean the same thing.
But most often you've probably trimmed them after you've pressed two Half Square Triangles open into a Triangle Square. When you do that, the Triangle Points are just poking out beyond the edge of the square and it's easy to see where to trim them off.
But there are times when
pretrimming the points is the way to go.
A good example is if you are sewing a triangle to a square.
The trick is to get the Triangle perfectly centered on the Square.
But because the edges don't match, you have to try to line it up by eye.
You can look at it this way. These Triangles are the same Finished Size as the Square and if you sew them together it will be the same seam line joining them.
If you look at the seam line on the Square, it is a Scant ¼" from each edge. So if you were to measure a Scant ¼" from the end of the seam line on the Triangle, that is where you would want to trim off the point.
If you used a die cutting machine to cut squares and triangles
this is how the pieces would come out. Just the finished size with an extra 1/4" all around
and the triangles wouldn't have any points to begin with.
If you accurately trim the points on Half Square Triangles and Quarter Square Triangles, their edges will match with a Square that is the same finished size.
The bottom line to all this is, the edges of Squares and Triangles that are the same Finished Size, should match exactly after you accurately trim the Triangle Points.
Long Side Trim:
Line the PrepTool along the Long Side of the Triangle
Short Side Trim:
Line the PrepTool along the Short Side of the Triangle
So which trim should you use?
You can usually tell by lining up the triangle to the piece you are trying to sew it to.
You should be able to see which way will make the edges match before you trim the points.
Example: Trimming Triangles for SquareinaSquare Units:
To make patches out of 3 or more triangles,
you may want to cut your squares into triangles first
If you cut a Square in half once diagonally, you'll make 2 Half Square Triangles. If you cut a Square in half twice diagonally, you'll make 4 Quarter square Triangles.
Start by cutting a strip into Squares
Color coded Purple
Cut the Square once diagonally to make 2 Half Square Triangles
Color coded Green
Cut the Square twice diagonally to make 4 Quarter Square Triangles
Color coded Red
A Double Friendship Star has four 3Part Squares
that are each made of one HST and two QSTs
Double Friendship Star
ColorCoded Breakdown
3Part Squares
An Ohio Star has four 4Part Squares
that are each made of four QSTs
Ohio Star
ColorCoded Breakdown
4Part Squares
It makes it easier to line triangles up when making 3 or 4 part squares.
Use a Short Side Trim on the half square triangles & Long Side Trim on the quarter square triangles.
Short Side Trim:
Line the PrepTool along the Long Side of the HSTs
Long Side Trim:
Line the PrepTool along the Long Side of the QSTs
They'll line up easier, and sew together easier.
It's also make it easier to sew the triangles together when you don't have to start on the points of the triangles. The points can get caught in the feed dogs of your sewing machine making it hard to sew in a straight line.
Brave New World units are a combination of:

1 Big Half Square Triangle

2 Small Half Square Triangles that are half the size of the big HST.

1 Square that is the same size as the small HSTs
Use both a Short Side Trim and Long Side Trim
to accurately line the triangles up to the square.
Use a Short Side Trim on one HST
Line it up to the square and sew right sides together
Use a long Side Trim on the other HST
Now the square and two small HSTs are ready to be sewn to the big HST
You can then trim the points on the big HST and the unit you sewed together so their points won't get caught in your feed dogs.
Double trimming makes it easy to line up two diamonds or a diamond and a square.
The PrepTool also helps to sew accurate scant 1/4" seam allowances & mark seam lines for precise setin seams. Learn More.