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A Nerdy Look at Longarm Quilting
(the nerdy engineer husband)

Preface: My wife said nobody wants to read all this dribble and quilters know all this already. However, I think that there are individuals that might like to know some of the things I have learned while helping my wife Jannette.

Longarm Quilting Machines
Over view:
Long arm quilting machines are sewing machines with a large harp, or throat. Just like a huge c-clamp can reach way in from the edge, the longarm machine reaches way over the quilt roller in order to sew in the quilting area. The longarm machine rolls on X-Y rails so that the needle can move over the space between two rollers. The width can be as wide as 14 feet and the sewing height can be 14 inches to more than 20 inches. When that area is complete you roll the now quilted section up onto the pickup roller in order to present a new area which comes off the backing roller. The sewing machine can be easily moved by hand with the pattern done free hand, or moved to follow a pantograph, or it can be driven by servo motors controlled by a computer program. When the needle comes down it is moving with respect to the fabric. In order to avoid a train wreak it is common to clamp the fabric with a hopping presser foot so that the fabric moves with the needle. This temporarily distorts the fabric in the immediate area of the needle. When the needle goes up the clamping is released and the fabric snaps back into its normal position.

Q&A - What do the terms "binding," "quilt," "quilt stack," or, "quilt sandwich" mean?

A quilt is made of three layers, a backing fabric, batting (insulation), and topped by a quilt top with those layers held together by either tying (yarn looped through the layers) or by being sewn together. The tying or sewing is the quilting and the composite is a quilt.

A quilt stack or quilt sandwich is the three layers described above..

The quilt is normally finished by binding the edge, where fabric is wrapped onto the edge in a C-shape and then sewn to the quilt stack.

What forces are applied to the quilt sandwich during the quilting process?

Pull, or tension, is the only force you can apply to fabric. ("You can't push a rope," or fabric either, for that matter.) Tension cannot be applied to the quilt top and batting because they just lay on the backing fabric before construction. The backing fabric is pulled (tension) by the rollers and side clamps. Additionally, as the quilting (sewing) occurs,  it pulls the fabric toward the interlock point of the top and bottom threads, where the needle goes through, because the mountain/valley contour reduces overall dimensions. This causes and overall shrinkage in the finished quilt dimensions compared to the starting dimensions.

What is a side clamp, or quilt side clamp?

Side clamps pull the quilt backing fabric from each side in order to prevent wrinkles from being quilted into the finished quilt, as well as balancing the roller tension, so that the weave remains square.

Why tension on the backing fabric matters?

Ideally, there should be no tension applied to the backing fabric, but realistically there must be some tension from both directions: side to side tensions and back to front roller tensions.
  • Roller tension is used to keep the fabric from drooping significantly between the rollers, while also removing back to front wrinkles, or ripples.
  • Side clamp tension, as mentioned above, is used to flatten wrinkles side to side, as well as, countering the roller tension and the tendency of the quilt sandwich to shorten side to side (and front to back) as the material sandwich is sewn in the quilting process.
The idealism of "no tensions" is that if the quilt sandwich could be just laid flat in a stack and magically held  together, there would be no distortion in the finished quilt. However, even if the backing fabric is pressed, there can be handling wrinkles or distortions that would keep it from laying absolutely flat. Batting, by its non-rigid nature, does not lie absolutely flat and needs to be smoothed to get all bubbles and wrinkles out. The last part of this sandwich is the top. The best quilters sew the pieces together very evenly with points meeting and no ballooning, but there are still seam allowances flattened to one side and minute dimensional variations that prevent the quilt top from laying perfectly flat. So we take the batting and quilt top as they come and rely on the integrity of the backing fabric,  knowing that it will get some tension applied to it. 

Unfortunately, there is commonly way too much tension added to the backing fabric by the rollers. I have even seen the fabric pulled ruler straight. At that point there is a very noticeable reduction in the width of the fabric. If the back is rolled back and forth between the rollers with tension applied, it is made even worse. And of course, if you are pulling on the weft (cross grain - selvage side to side, parallel to the rollers) you will get the most stretch and the sides will pull in the most. If you are pulling on the warp (grain - selvage roller to roller) you will get the least stretch. However, this may result in material being seamed to get enough width. As a result, you will be rolling at least two layers of fabric (if you open the seam) and three layers (seam not opened), causing the diameter on the roller to increase faster than where there is a single fabric thickness. The result will give you uneven tension along the width of the rollers. This can lead to puckers in the back when quilting. (Therefore, knowing this, you may want to run the seam side to side and pull even less on the side clamps than you might otherwise pull.) The hourglass distortion of high roller tension will be sewn into the quilt sandwich. When you remove the finished quilt from the machine there will be a permanent variation sewn into the quilt and the side edges do not lay flat in the same plane as the rest of the quilt.

Likewise, if you pull hard side to side with the side clamps, you will distort the backing fabric while it is being attached to the sandwich. If you are using point contact clamps, the distortion will be localized and amplified. As a result, you will get a scalloped edge when the quilt is removed from the machine. We have all seen quilts hanging in quilt shows with a cyclic distortion instead of being nice and straight.

Additionally, if the fabric is tightly stretched it cannot be clamped and immobilized for the needle passing through it. The result is deflection of the needle and distorted stitches, among other things.

Pulling hard on both the rollers and the side clamps makes everything worse and you get ruffling.

There is one thing I know for sure - my wife's side clamps are outstanding in speed and ease of use, while providing an unexcelled finished quilt.

Click here to see specifications for Jannette's Professional Quilt Clamps.