The sides usually have clamps or other devices to hold the quilt taut. We also use the sides to prove the thread tension for the specific quilt, as shown with the curvy "C" designs, shown right. All this takes fabric.
Additionally, with many edge-to-edge designs the stitching continues off the edge to get a good fill of stitching on the top. This is because a design is a single line, going up and down and back and forth in order to fill in the design. Both the backing and batting must be larger than the where the "foot" may travel or the foot may "catch" the batting and/or backing and stitch it onto the top. Having sufficient backing and batting allows the quilter to continue without catching the fabric.
The batting sizing has the same issues as backing. However, there is an additional issue with batting.
When batting is very fluffy, there is a tendency for the backing and/or batting to be "consumed" by the quilting process faster than the top. Everything at the bottom of the quilt runs out of batting and backing before the stitching is completed. This can be disastrous when the quilt has custom borders and the border can not be stitched.
In prior newsletters I have presented the issue of squaring a back [LA#11], a process in which you inevitable loose some backing fabric. Also presented was the loss of fabric through pre-washing [LA#7]. Again, both of these reduce the fabric size of the back from when it was first purchased and seemed to be the correct size..
In a longarm studio, quilts are being loaded and unloaded. Each quilt has a different quality of fabric used in the top and back as well as different batting, depending upon each of the piecer's preferences.
Each of these affect where the thread's knot will be located within the quilt. Will it be in the middle where it should be? Or, will it be on, or near, the top or bottom? - Yuck!
As this changes from quilt to quilt, the tension must be tested on the backing and batting being used - the top piece can be a quality scrap. This takes room at the sides of the quilt - not much, but some and possible in several places as the quilt advances. This is show in the first photo.
Only Your Longarmer Knows
Always check with the longarmer that you are going to use to determine how much backing fabric and batting is enough. At Forever In Stitches we want 10" of backing fabric beyond the top, or 5" on each side. The batting should be 5" larger than the top, or 2 1/2" on each of the sides..