Math Tricks with Specialty Rulers!

I received an email from Vicki in Australia asking for some math help with figuring the sizes of strips she can use with the Easy Angle Ruler and Companion Angle Ruler while making the Lazy Sunday mystery that is currently running in Quiltmaker Magazine.

She writes:

Hi Bonnie
I have a question about Part 2. For the  4  1/4 inch squares what size would I cut them into triangles with using the ruler? I am having a mental blank. I have started doing the large completed units.

Vicki

 We’ve all had those mental blanks before!
 
Before I go any further – this photo has NOTHING to do with the mystery currently running!  It’s just a photo from my archives of Quarter Square Triangles.  I wanted a photo that would be a grabber enough for you to stay and read this post ;c)
 
When working with specialty rulers like the Easy Angle and Companion Angle rulers, the first place you need to start is to find the FINISHED size of the unit you are making.  Sometimes a pattern with "regular rotary cutting directions" will list that, sometimes it won’t. Sometimes you can look at the finished size of the whole block and deduce what size each unit in the block should measure.
 
Because this is a mystery, and I haven’t received my issue yet, I’m not sure of how Quiltmaker has broken the steps down ---But with a bit of reverse algebra –let’s assume the following.
 

 
The magazine lists the cut square size as 4-1/4”.  If this is the unit I am thinking of – the finished size of the unit is 3”, so likely we are making quarter square triangles here.
 
Remember the math formula for Quarter Square Triangles?  Take the FINISHED size of the unit, and add 1-1/4” to give you the size of the square you need.  From here you proceed to cut that square with an X from corner to corner to give you four quarter-square triangles from each cut square.
 

 

To use the companion angle ruler for these units, instead of cutting 4-1/4" squares, find the "FINISHED SIZE" of the quarter-square unit.  In this case I believe it is 3" (Again I don't have a copy of the magazine yet so I don't know how they broke the steps down)  Divide 3" in half = 1.5" (Because an hour glass unit is two triangles high!) Now add the seam allowance to that bringing it up to 2".  You will use a 2" strip and the companion angle ruler instead of cutting a 4 1/4" square with an X.
 

 

And it’s even easier than that – do you see those LARGE Numbers on the outsides of the Companion Angle Ruler?  Those are the finished “Hour Glass” sizes.  The numbers down the CENTER of the ruler tell you the size of strip to cut in order to get that size of finished unit.
 
It’s easier than you think to find out what sizes of strips you need --- but you need to start by finding the finished UNIT size before you can figure out the rest!
 
Something else to consider when finding what sizes of strips to cut for the quarter-square triangles in Flying Geese units:
 
The height of a flying goose unit is only HALF the height of an hour-glass unit….so if you know that your goose is going to finish at 2” X 4”  Add 1/2” to the 2” side to give you 2-1/2” and you’ll be cutting your goose triangles from a 2-1/2" strip.

OR:


Follow the large numbers on the outside of the ruler and take the FINISHED SIZE of the LONGEST EDGE of the flying goose unit --which will be 4".  ((It's 2" X 4" finished, right?))

Now  find the corresponding small number down the center -- see?? 2.5"! This way also tells you to cut 2.5" strips for flying geese units that finish at 2" X 4".
 
What about Half square Triangles?  How do you know which size of strip to cut for using the Easy Angle Ruler?
 

 

 

 
The “regular” rotary cutting method is to add 7/8” to the finished size of the unit to give you the size of strip or square you need to cut to get your unit to finish at the size you need.
 
Half square triangles that finish on the even INCH will have a measurement that says “Something + 7/8”.
Half square triangles that finish on the HALF INCH will have a measurement that says “Something + 3/8”.

There are two ways to figure out what size of strip to cut to use the Easy Angle Ruler.
 
Find the finished size of the unit and add 1/2”. (regular seam allowance) As in –the units finish at 2”, therefore I’m going to start with a 2-1/2” strip.
 
OR:
 
Take the cut measurement given, and subtract 3/8”.  That will tell you right off what size you are going to cut.  If the pattern calls for a 2- 7/8” strip – I know I can subtract 3/8” and have 2-4/8” which is 2-1/2”.
 
((Oh, I wish my 7th grade math teacher could see that I DID learn my fractions after all, but it took Quilting to make me understand it!))
 

This comes in handy when you need a unit that finishes on the half-inch in a quilt.  The pattern will tell you for a  half-square triangle unit that finishes at 1-1/2” to cut a 2-3/8” strip, cutting that strip into 2 3/8” squares. 
 
Subtract that 3/8” to use the Easy Angle – and you’ll be cutting your units from a 2” strip.
 
Easy Peasy, RIGHT?!
 
And do you know what that extra 3/8” is anyway?? Whether the measurement is 7/8” or 3/8” – that extra 3/8” is simply a DOG EAR.
 

 
You are going to remove that Dog Ear  before sewing your units into the quilt anyway – so why not remove them before you even sew and get more units out of less fabric in the long run using the Easy Angle and Companion Angle rulers!
 
No more Triangle Trouble – it’s all smooth stitching from here!