Thursday, March 14, 2013

It's Pi Day! (And how it relates to crochet)

Celebrate Pi!

I ♥ Pi!
As a thread crocheter who loves to make doilies and design in the round, I've come to love pi! I'm not a math person by any stretch of the imagination. If I have to do mental math I'm always off by a factor of 10. Designers all know that eventually it all gets back to the math when working a design.

Stitches per Diameter Inch (SPDI)
I was having a struggle with my very first design until I realized a very important equation concerning pi would help me tremendously. I call it stitches per diameter inch (SPDI), and is probably called by some other terms among other crochet designers and knitters.

To discover what your SPDI value is, work up a circle of dc stitches to 1" in diameter. Count the number of stitches. Example: On a size 1.25 mm hook with size 20 Lizbeth thread, 36 stitches = 1" diameter. Thus, my SPDI is 36 stitches. If I wanted to make a doily that is approximately 15" diameter, the last round would need about 540 stitches.

Knowing your SPDI is helpful if you are working with a different thread size than what a pattern calls for and want to know the final diameter of the doily with the smaller (or larger size) thread. (The math for that is a little more involved and I'll save that for another post.)

Stitches per Circumference Inch (SPCI)
This numeric value is important when making things to wear, like a necklace, hat, sock, sweater, etc. When I designed my first barefoot sandal I needed to know what is the average circumference of an adult woman's ankle. The average is about 11". Using the value of 36 stitches from above as an example:

36  ÷ 3.14 (value of pi) = 11.46 (sts per circumference inch)

Round up to 11.5 stitches per circumference inch: 11.5 x 11" = 126.5 dc stitches or thereabouts*

*When I crocheted up a swatch it took only 124 dc stitches.

Want to learn more about pi and Pi Day? Click here.

What are your favorite types of pie?
More About Pi(e)
My other favorite use of pi was in the book Contact by Carl Sagan. 

I also am very fond of pie. I'm very fond of cream cheese, key lime, blackberry pie, and beef shepard's.  My least favorite pie is banana cream and steak and kidney. 

1 comment:

  1. About the only pie I truly think of is the French silk at our favorite eatery.
    I use Pi subconsciously I am sure. But I have always worked more artistically than mathematical.
    I realize it is an important element but don't ever expect me to explain it like you have. I admire those of you who do think like this. It's a gift in and of it's self. Embrace it.