HST - QST - and Fuzzy Math -

The other day I had an email in my inbox from the Quilting Company with a link to an article about overcoming fuzzy quilt math - HERE -

It's a "sponsored" post -

January 28, 2019
Author: Guest Blogger -

The "Guest Blogger" turned out to be John Brady of Guidelines4Quilting™

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He explains the "fuzzy math" problem very well -

The built-in error occurs when you’re cutting a square diagonally to make triangles.

And he explains how he designed some "extension bars" to solve the problem - ;))

I'm a math geek - so I thought it was a VERY interesting article -

And he makes some good points -

But I noticed a few things as I was reading along -

And I have a totally DIFFERENT solution to the problem - ;))

If your quilt pattern includes a quilt block with triangles, it also includes a built-in error. And it’s all because of your rotary cutter.

Hmmm - Not necessarily - the built-in error part - because of your rotary cutter.
I think it has more to do with the method used than the rotary cutter itself - ;))

You probably thought that if your triangles didn’t match perfectly with your squares, there must be something else going on—maybe you didn’t cut as accurately as you thought, or the problem was sewing them together on the bias.

Then he goes on to say -

As you may probably know, we are told to add 7/8″ to a square that will be cut in half for Half-Square Triangles, and 1¼” to a square that will be cut in quarters for Quarter-Square Triangles.

I agree that we are told to add 7/8" and 1-1/4" -

BUT -

Who says we all cut a square and then cut it in half for a HST? -

What if you cut a strip and want to cut a HST from that? -

Before rotary cutters, quilters just made templates (some of you may remember cutting shapes from empty cereal boxes). The only seam allowance measurement a quilter ever needed to know was a quarter inch. Making templates and cutting with scissors was tedious, but there was no complicated seam allowance math. You simply drew your triangle, and add(ed) a quarter inch all around.

Haha - that's EXACTLY what I did when I designed the LEFT-EZE™ Rule -
I drew a triangle and added a quarter inch all around - ;))

It was much faster to use a rotary cutter and ruler to cut squares and then cut them diagonally into Half- or Quarter-Square Triangles. But if you did that, you would obviously need to add more than the standard half-inch, because you needed the extra quarter inch on the diagonal edges as well.

Is it really faster to cut squares and then cut them diagonally into HST and QST? -

I know I do that when I'm cutting Side Triangles and Corners - but that's because they are so big - and I usually cut them oversized and trim them down later -

Sometimes I just have a bunch of strips that I want to use - and I want to cut HST and QST from them -

But I agree with the "you needed the extra quarter inch on the diagonal edges as well." -

The built-in error occurs when you’re cutting a square diagonally to make triangles.

So - don't cut squares diagonally to make triangles - problem solved - LOL - ;))

And - last but not least -

finished-size math.

I know pattern designers use "finished" size math - but I don't really care what the "finished" size is to start with. If I have some strips or "units" already sewn - all I want/need to know is what size cut square I can match to it - and if I subtract 1/2" for the seam allowances - that tells me the "finished" size -

What I really want to know is the "unfinished" unit size - OR -

Which bag of pre-cut strips do I pull for this project? - LOL - ;))

The built-in error occurs when you’re cutting a square diagonally to make triangles.

So - yes - there is fuzzy math if you cut a square first and then cut HST and QST -

Because of the rounding of the additional 7/8" and 1-1/4" -

BUT -

I said that I have a totally DIFFERENT solution to the problem - ;))

First - I don't cut a square diagonally to make triangles - I cut them from strips -

Second - I use a triangle ruler/template with the seam allowances built in -

And Third - I forget about the "finished" size - ;))

If you're trying to follow a pattern that gives "finished" size -

You can use the FREE SIZE CHART to figure out what size strip you need -
It even has columns for patterns that say to cut a square -

LEFT-EZE™ RULE - SIZE CHART - NO MATH REQUIRED
Easily find the STRIP WIDTH needed to make the size you want -;))

***NOTE - IF THE PATTERN SAYS TO CUT A SQUARE -
USE THIS COLUMN TO FIND THE STRIP SIZE YOU NEED

Or you can make something from the strips that you have already cut - ;))

In the olden days -

No fuzzy math -

You simply drew your triangle, and added a quarter inch all around.

Yep - that's what I did when I designed the LEFT-EZE™ Rule -
I did it the "old-fashioned" way - and it works quite well - ;))

I take two strips - right sides together - line up the ruler -
With the black tip on the top -
You can SEE the 1/4" seam allowance on the diagonal -
The same 1/4" is "built-in" on the side and bottom -
So you don't need to worry about it -

Make the second cut -
You can see the SAME 1/4" seam allowance on the diagonal -

And - sometimes - for some reason - my second cuts are a "smidge" too big -

So when that happens - I trim it now -
It saves me from having to trim the HST after it is sewn -

Sew it from the flat top side - 1/4" seam allowance -
The flat top is the dog-ear that is automatically cut off because I used a strip -

Press it open - and I have a perfect 2-1/2" HST -

That will match a 2-1/2" Square -

With NO Fuzzy Math - ;))

Doesn't get much easier than that -

And the same goes for - QST -

I use the same ruler to make perfect QST -

With NO Fuzzy Math - ;))



Talk to you later - gotta go - gotta sew -