Not all 2-1/2" strips are exactly 2-1/2". Ballipops are hand cut inBali so there is some variations there.
Here's something I found that assures us 2-1/2" strips when sewn.
When sewing two strips together, rather than measuring 1/4" to the right of the needle position, I measure 2-1/4" to the left of the needle. A piece of blue painter's tape is placed along the left edge of the 2-1/4".
The fabric strips are positioned right sides together, paying close attention to keep the raw edges aligned at the left edge. As the strips are sewn together, care is taken to keep the left edges alligned with the tape strip. If there is any variation in strip width, it will fall within the seam allowance.
The sewn strip is pressed and the width measured. The seam allowance is narrow in some places and wider in others, but the finished width is consistently 4-1/2" wide. This method works to correct the strips used when 2 strips are sew together and then sub-cut.
When sewing two strips together using this manner, you will need to adjust the way you hold the strips and where you watch the trips as they are being fed through the sewing machine.
While it is not a cure-all, it does put your pieces will on the way to accuracy when the project begins with strip piecing.
It's so much easier than it sounds. Give it a try. Save on wasting strips.
Hope this helps everyone. Some patterns really rely on the strips being accurate or it throws off the whole block.
I read this originally in a book by Brenda Henning so please give her credit for this wonderful tute. Thank you.♥♥