This is the start of mounting a quilt on my longarm. The backing is on the bottom, attached with my Red Snappers. Next is the batting layer, and on top is the quilt. This is a fairly small quilt, but with only a couple inches on each side of the backing, I needed to attach my extensions for the side clamps. Side clamps are really a necessary accessory. There are many styles and configurations for these clamps, but I created my own version which started with a lap quilt frame using PVC pipe and bungee cord. The frame I bought at Joann's and was for a 12" square. I bought a longer piece of PVC and cut two 24" pieces to replace the 4 - 12" pieces from the package. The PVC I bought is the one used for hot water (cream colored as opposed to white), as it is has a slightly bigger dimension, which helps the clip-on tubes hold a little tighter. The bungee cord attaches to the side of the frame with adjustable pinch slides, like you would find on a jacket. I know I am not using the appropriate terminology for some of these parts, but I think you can figure out what I am talking about.
When the backing is not wide enough, I use extensions for the side of the backing which is made
from about 5" off the bottom of a t-shirt. One side is the hemmed
edge. The other side I cut 1/2" longer to allow for a hem. The
purpose of the hemmed edge is to prevent the clamp tubes from sliding
off... unexpectedly sometimes. The edge that is pinned to the side of the backing is a raw cut
edge... t-shirt material does not ravel. I use hat pins, almost end to
end, to secure the extension to the backing. The side clamps only hold
onto the backing and does not include the batting or the quilt top.
If my backing is wide enough, and extensions are not necessary... I keep a 2" wide strip of batting handy to lay on the backing fabric edge before attaching the clamp tubes, which keeps the clamp tubes from slipping off.
I sew the batting down across the top, creating a straight line to line up the top edge of the quilt top before stitching it down almost on the same line... I roll the take-up bar one or two clicks so the stitch line is about 1/4" from the edge. This is followed by stitching down the sides of the quilt. This stitch line is not critical to be exactly 1/4"... in fact a little shy of 1/4" is ideal, but it is very important to stitch the sides down. If I run off the fabric, I typically will stop and move the needle over. This side stitching is in the border area that will be covered by the
binding, so if it varies in width... it will not show when the quilt is
done. Having a stable surface to quilt on makes an enormous difference on your outcome.
When I start my stitching I bring my thread up in the border, still on the quilt top, but outside the stitch line. It is not necessary to lock the stitches down on the edges at this point as they are outside the stitch line and they will be locked down when the binding is added. An important tip though... all loose ends need to be locked down before your quilting is done.
I think all quilting rules have exceptions, and many of my steps may not always be needed... but I do them because they work for me. Shortcuts might get you done faster, but the end result is often compromised.
In summary... The backing needs to be taut and the quilt top needs to be secured to the quilt sandwich on all sides.