Tuesday, January 27, 2015

Prairie Points Part 1–Sizing and counting

Prairie points 1

This is the first installment of the Prairie Point Tutorial series.

The prairie point tutorial I planned to post a few weeks ago is a little later than I anticipated.  As I wrote, questions that a first-time prairie point user might ask kept popping up.  For example: OK, that’s how you put them on, but how do you choose a size?  How do you know how many to prepare? How much overlap should there be? The post would have gotten rather long and unwieldy! 

With that in mind I stopped writing, sorted the thoughts popping into my brain, placed everything in what I think is a logical order, and started over.  Here’s the new plan:

If you haven’t tried adding prairie points to a quilt, I hope this series will inspire you to give it a try!

*************************************************

If you have a pattern that tells you what size to cut the squares to fold into prairie points, and how many you need, you’re all set and you can skip ahead to part 2.  If you don’t have a pattern but want to add prairie points to a project, read on!

1. Choosing a finished size for your points

Do you like big, hearty points, or smaller dainty ones?  This is really a matter of personal preference and will probably vary according to the project.  What looks just right on one project might look huge on another and too dainty on the next. 

You’ll need to audition different sizes, but I recommend using paper squares to do so.  Why cut up precious fabric until you know you know exactly what size will work?

Sizing points 1Sizing points 2Sizing points 3

Start by cutting about 6 squares (all the same size) out of scrap paper and folding them in half along the diagonal, then in half again.  That will give you paper prairie points to play with.

Point height 2As a guide to what size square to start with, the height H of the triangle will be 1/2 the length S of the side of your square.  (Notice that the base (long side) of the triangle ends up being all 4 sides of the square stacked together.)  So a 3” square will give you a 1.5”  tall paper triangle.

Point overlap 3Point overlap 4

Lay these paper points flush with the edge of your quilt and decide whether you like the size.  If not, start over with smaller or larger paper squares, until you find a size that you think looks good for your quilt. This is the size you’ll want your finished prairie points to be.  Play with how much the triangles overlap, too. 

Leave your paper points laid out how you like them.  You’ll need to do some measuring in step 3 to figure out how many points you will need.

 

2. What size do you cut the fabric?

Now you know what you want the finished size of the prairie points to be, but how big do you need your fabric square to be so that your folded prairie point will be the desired size after the seam attaching it to your project takes a bite out of it?

You will sew your fabric prairie points to your quilt with a 1/4” seam allowance.  Here’s the math to add the allowance:

Size to cut fabric square = size of paper square + 1/2”

For example, if you liked the point size you got from a 3” square, you’ll need to cut fabric squares that measure 3 1/2”.

If you’re skeptical that 1/2” is the correct amount to add, cut a paper square. For my example, I want a finished point just like the one I got when I played with a 3” paper square.  For the corresponding unfinished point, I claim I’ll need a 3 1/2” square, so that’s the size I’ll cut this paper square. Draw a line 1/4” in from the sides, all around the square, to represent 1/4” seam allowances. That gives me a 3” square with a 1/4” seam allowance all around. Fold your square as you did the paper points and look at where all that seam allowance ends up.

IMG_9213IMG_9215IMG_9216

Yup!  There it is, all in that 1/4” at the base of the triangle.  The center 3” square made the finished 1 1/2” tall triangle, just like my 3” sample paper square earlier, and the extra all around is now stacked into the bottom 1/4” which would be eaten up by the seam when I sew this point to my quilt.

3. How many points do you need to make?

You’ll need to do a bit of measuring and a bit of math.  Don’t panic!  If math isn’t your thing, just measure and plug numbers into the formula. If you do like math and want to know where the formula came from, scroll down to the bottom of this post.

Prairie points spacing measurement 3

  • Measure the length L of one edge of the quilt.
  • Remember that S is the length of the long side of your finished prairie point.
  • Measure the distance X, as shown above, between one end of the triangle base and the spot where the next triangle starts overlapping. I marked that spot with a red arrow on the paper in the photo above.

Now plug those numbers into this formula:

Number of points = [(L – 1/2” – S) / X] + 1

Be careful to follow the math order of operations.  Calculate (L- 1/2”- S) first.  Then divide that by X.  Then add 1 to that answer.

That probably won’t work out to a nice whole number. Just round to the nearest whole number (down for a fraction less than 0.5, up for everything else) since you’ll be using only whole prairie points, no partial points.

For example if one side of my quilt top is 13” long (L=13) and I want the base of my finished points to measure 3” (S=3) and the distance X = 2 1/4”,  this is the math, step by step:

Number of points = [(13 - 0.5 - 3) / 2.25] + 1

Number of points = (9.5 / 2.25) +1

Number of points = 4.22 + 1

Number of points = 5.22

Round that to the nearest whole number, 5.  I would need to prepare 5 prairie points for this side of the quilt. 

Repeat the math for each edge of the quilt.  For most quilts, the top will need the same number as the bottom, and each side will need the same number.  However, if you’re quilting outside the box and your quilt isn’t the usual square or rectangle, just do the math for all 4 (or more!) sides and add up the totals.

 

******************************************

For more information about prairie points,check out the rest of the Prairie Point tutorial series:

******************************************

 

For those of you who care, here’s where the formula came from.

Number of points = [(L – 1/2” – S) / X] + 1

That 1/2” you’re subtracting has to do with seam allowances. Since we are working with the finished point size, we want to be calculating with the finished length (L – 1/2”) of the side as well.

X is the amount of space you have to allot for each prairie point except the last. You can see in the diagram below that for the very last triangle on the end of a side we have to account for the whole length S of the triangle base..

Counting

So the formula takes the finished length of the side, takes away the space S covered by the last, whole prairie point, then divides the remaining length by X to see how many times X fits in that length.  There’s 1 prairie point per X.  Add that whole prairie point back in, and you have your total.

6 comments:

  1. Fascinating calculations! And your paper test is brilliant. I have saved this for when I find the perfect quilt to add them to.

    ReplyDelete
  2. I will know where to go if I ever put PPs on something! Thanks!

    ReplyDelete
  3. This is brilliant Joanne! I like how you've separated the lessons too. I've pinned this to Pinterest so I can find it whenever I decide a quilt needs Prairie Points!

    ReplyDelete
  4. OOOhhhh...I get that formula! I DID care...and it makes perfect sense. I'm glad I read it through because I think I would have been, "side of the quilt" - does she want finished or unfinished? Good you explained it! You would have been a terrific math teacher. :-) Great informational, tutorial post.

    ReplyDelete
  5. Great tutorial! It has been years since I did prairie points but I always loved them.

    ReplyDelete
  6. This is fantastic Joanne. I wish I had your tutorial when I was making Under the Sea baby quilt. My maths teacher was right - calculus is something I would use later in life. Have already printed the pages to file. Thank you!

    ReplyDelete

Thank you for visiting. I enjoy reading all comments and I aim to reply by email, though yahoo mail and no-reply settings can sometimes get in the way. If your Google account is set to "no-reply" I have no way to contact you, but know that your comments make my day just the same!