I have a long arm and didn't give a lot of thought as to how the seams should run on a pieced backing, until I pieced one vertical. As I quilted, there grew to be a mound in the middle of my frame and the sides of the quilt were slightly slack. I ended up having to work and pull different sections of the sides as I quilted them to avoid puckers and little darts. Now, I make sure the backing seam is either on the diagonal or horizontal to the quilt.
If I have to piece the back, I do my backing seam as 1/2" and I do iron it open. I have not had any problems with batting pulling through. I do use a 1.8 or 2.0 as my stitch length.
For the backing and batting, I do add 10" to the overall width and the same to the length of the quilt to allow for positioning the quilt properly and for a practice sewing area when I have to change the bobbin. My older Nolting can be a challenge if I don't do this. It tries to forget everything it knows about sewing if I don't do a few stiches on the edge to make sure the mind is still there. Mostly it is my fault, because I don't always get the bobbins wound just right. I've learned to check them over very carefully.
Last edited by Barb in Louisiana; 09-20-2017 at 05:59 PM.