Let me say straight out that Longarmers cannot perform miracles. I recently got a quilt from a quilter that had never shipped a quilt to a longarmer before, and we ran into a bunch of different problems. Here’s some lessons learned that may help you out:
1. The quilt backing needs to be 4″ greater than the quilt in all dimensions (that is, 8″ longer and wider than the quilt top). This is for two reasons: because we stabilize the backing side-to-side with clamps, the clamps cause some distortion to the backing. Having 4″ on each side dissipates the distortion, so you don’t notice it by the time the quilt top matches up with the backing. Also, it allows for space for the clamp itself! Then, having 4″ on top and bottom allow us to pin or attach the backing to the frame. We need this extra space because we can’t quilt on top of the frame leaders. Also, because the quilt rolls up onto rollers on either side of the frame, the backing has to be slightly bigger than the quilt top to account for this. (Think of rolling up a phone book and how the pages spread out).
2. Don’t piece your backing any more than necessary. Backing is under tension, and extra seams do not help. Also, remember that longarmers cannot exactly match backing seams to front seams — we do not pin the quilt together like you do when you quilt a quilt on a domestic machine. We do our best, but ultimately cannot control the backing exactly with the top (see the phone book point above).
4. Try to pick a backing that matches the thread you want to quilt the top with. No matter how much we mess with the tension, we cannot always get a black top thread and a white backing thread to perfectly knot in the center of the batting. Tension shifts as the machine goes through curves and different directions, and it is impossible to avoid some “pokies” with really dramatic thread differences. Having similar backing fabric and top thread choices alleviates this issue. Or, if you want, you can quilt with the same color thread, as long as you are willing to have contrasting thread on the back. Your choice.
5. Make a good attempt to clear out extra hanging threads from your quilt, especially if you have dramatic color changes. We do our best at picking up stray threads, but the worst thing that can possibly happen is a dark color thread falls off your quilt top into a light block, and it is not noticed until the quilting is done. You can help reduce this risk by making your quilt as clean as possible, and removing any stray threads that you can. If you press your quilt ahead of time, you can ensure that all your seams are going in the right direction, and you’ll catch all those threads at the same time.
I hope this helps explain some of the strange requests your longarm quilter makes!