Originally Posted by
JenniePenny
There are 41 blades in the picture of the pattern shown. If one were dividing/ drawing a circle into 9 degree increments, yes that number of blades is 40. But quilt math is not the same as real math because you are sewing all those pieces together and losing the equivalent of one whole blade with all the seam allowances. Don't worry about the angle. Just like only in 'quilting math' does 2.5 + 2.5 equal to 4.5. (Take a 2.5" square, sew to another 2.5" square, and you will not get a 5" square as a result.)
I agree that you have allow for seam allowance in the size of the patch, but seam allowance does not affect the angle. if you sew a square patch, you wind up with a smaller square, but the angles are still 90 degrees. if you cut a wedge with a 9 degree ruler, sew it to its neighbors, you wind up with a smaller wedge, but it's still 9 degrees (if you sewed perfect seam allowances) and it will still take only 40 perfectly cut and sewn wedges to make the circle.