Is Your Backing Always Loose on One side and Tight on the Other?
Is the backing really square? I personally do not cut my backings—I square them by tearing the fabric. I measure the backing making sure it is larger than the top. Then I cut a little clip mark about 1 inch into the fabric in the direction that I want it to rip. With a snap I rip the fabric quickly. Tearing slowly will cause more threads or strings. The rip line will follow right down the thread. This is what we call thread straight. Then we know that we have the same thread count down one side as down the other.
One of the most common things that can happen is the leader cloth or fabric aprons on the machine slip where they are attached to the poles. See in the picture and note how the Velcro attachment on this pole doesn’t go straight down the pole but has a twist to it. We would need to pull this off the pole and straighten it up. Some poles will except carpenters glue and that will reattach the Velcro. Some of the painted poles need a permanent bead glue to hold the fabric to the pole. Both glue types will need to dry for 24 hours. I am sure there are other types of glue that will work.
Even after you get the aprons on the poles straight you can have the fabric leader cloth be stretched out of shape a little. That could cause a pantograph style pattern to not line up with the patchwork and look like it is going uphill. So here is a quick tip for that.
Place your quilting machine at the center mark of your pinned on fabric. You are going to measure from the middle because the poles can have enough tension on them to bow a little and the measurement would be smaller in the middle than on the end. So it is best to measure from the middle.
If you have a computerized quilting system or a manual channel lock you can put the vertical channel lock on.
Sew a line of stitching across the quilt on top of the batting. It will secure the batting and give you a destination to lay the quilt top edge to. That line is straight with the tracks of the machine. That means that the computer will sew straight with that or if you are hand guiding a pantograph it will also be straight. You just have to make sure the patchwork lines up with the tracks. Now your should get nice straight rows with your quilt.