Primary Stitch Control Factors, Part 2

Stitch length, density and underlay all impact embroidery quality. In Part 2 of this series, learn how to correctly manage underlay.
March 1, 2008

Sew this fill pattern with a run stitch border to test push-pull factors.

By Jimmy Lamb, Contributing Writer

Embroidery digitizing technology has come a long way. New developments in software and high-speed hardware have brought many advances to the design creation process. Jobs that once took hours to complete can now be done in minutes. But as the industry has become more dependent on technology, the knowledge required to produce elaborate, top-quality embroidered designs has been pushed aside in favor of bells, whistles, shortcuts and automated functions.

Technology is not a bad thing as long as it's used to enhance the process rather than replace it. Though software certainly enhances the effectiveness and efficiency of the process, it's ultimately skill and knowledge that define a digitizer's true ability. Too often, however, new digitizers focus on using default values and allow software to make decisions instead of experimenting themselves to find out what works best for a given situation.

To create an exceptional design that sews and looks great, you must be in total command of the stitches, which are the building blocks for embroidery. Just selecting the best type of stitch for the application is not enough: You must understand what it does to the fabric, what the fabric does to it, and what effect it has on previously laid stitches and on stitches yet to come. Thus, you must control it by addressing and setting the various parameters associated with the chosen stitch type, known as the "primary stitch control factors."

The primary stitch control factors are: stitch length, density, underlay and pull compensation. In Part 1 of this article in last month's Impressions, we took an in-depth look at stitch length and density. This month, in Part 2, we'll round out our examination by discussing the importance of underlay and pull compensation.

UNDERLAY
Underlay, the third stitch control factor, is probably the most important aspect of any design, yet it remains invisible in the finished product.

Much like the foundation of a house, underlay is the foundation that supports the design that will be placed on top of it. The decisions you make about what underlay to use can affect every forthcoming detail of the remainder of the design. Thus, it should not be treated with casual indifference.

Keep in mind that with virtually any design, your first goal is to stabilize the fabric of the garment. Simply placing backing in a hoop does nothing at all until it is joined to the garment via the sewing process. Therefore, your initial underlay stitches should be created manually (using run stitches) so as to stabilize as large an area as possible as quickly as possible. (Note: Anything that zigzags — even run stitches — can lead to push-pull problems, so your initial underlay stitches should not zigzag. See last month's article for more detail.)

Once initial stabilization is accomplished, your next step is to provide a secondary level of stabilization, followed by a solid foundation for the stitches that will come later.

Using a soccer ball as an example, your first underlay segment should probably be a run stitch that starts at the bottom and goes straight up through the center of the design to the top edge, and then follows the outside edges of the design (about 1/4 inch or so inside the outer edge). Go around a couple of times, ending at the top of the circle you've created.

Once your initial stabilization is complete, it's time for the secondary level. Starting at the center, create a wide zigzag pattern, from top to bottom, moving out to the right side of the design within the confines of the circle. Run straight back to the center and repeat on the left side. Now, secondary stabilization is complete.

Two important things to note so far: 1) The initial underlay stitches didn't zigzag, so they provided stabilization without potentially distorting the fabric. 2) The secondary stitches did zigzag, but the initial underlay stitches helped to minimize any push-pull effects. Furthermore, because they started from the center and worked toward the outside edge, any pushing would be equally balanced between the two halves of the design.

It's now time to apply the final phase of the underlay — the foundation stitches. The first two levels of underlay were done manually using run stitches in order to assure exactly where and how they were sewn. The foundation portion can be done using an automatic underlay selection such as a nice cross-hatch pattern, the result being additional stability plus a balanced platform to support the top stitches.

Another useful purpose for underlay is to create raised or textured areas within a design. For example, if you wanted a tree trunk to look round instead of flat, you could use a couple of layers of satin underlay, each wider than the one before and at angles to each other to prevent stitches from sinking. Because they are underneath and at angles, you can keep the density fairly low. When the final top stitches go into place they will have a slightly rounded look, giving the design some extra flair.

PUSH-PULL COMPENSATION
Push-pull compensation is perhaps the most challenging aspect of all in terms of digitizing. During the sewing process, certain areas of a design may mysteriously shift in position, change shape or change size. For example, you sew a circle using a fill segment for the inside and a run stitch border. It looks perfect on the screen, but during sewing it turns into an egg shape with the fill stitches not reaching the border on the sides, but protruding past the border on the top. The design "pulled" in from the sides and "pushed" out at the top. Welcome to the world of push-pull.

In general, anytime you sew something that zigzags (satin or fill), it has a tendency to pull in from the edges and push out in the direction that the segment is moving, the degree of which is influenced by the fabric being sewn on.

These two forces are a function of the stitch formation process. When a stitch is formed, the bobbin thread "pulls" down on the upper thread. If the fabric is stiff, the amount of "pull" is minimal, because the sturdiness of the fabric counters the force of the downward pull.

On the other hand, soft stretchy materials tend to give more to the pulling action, allowing the stitch to sink further down into the fabric. This, in turn, compresses the fabric and forces it to shift slightly in the direction that the segment is moving. Over time, this can cause an elongation of the stitch segment, which results in the "pushing" action. Another symptom is that the fabric may pucker as it gets forced in the direction of the "push."

If the stitching is in a zigzag pattern, then the same sewing forces will pull the outside edges of the segment being formed toward the inside, again influenced by the stability of the fabric.

There are two basic ways to deal with push-pull forces via the digitizing process: proper underlay and stitch compensation.

Take a look at the circle design (pg. 55) composed of a fill pattern with a run stitch border. The ideal shape (artwork) is defined by a solid line. However, if you digitized it as you see it, the result would probably look like the solid area of shading — an egg. In addition, if the segment started at the bottom and worked its way to the top, you would probably see a few stitches protruding above the top edge.

The first approach is to control the push-pull effect via proper underlay, as described earlier, which will probably knock out the majority of the problems. But if not, then you will move to the compensation phase. This means purposely distorting the design in such a way that the push-pull forces will counteract your commands, with the result being ideal stitch placement.

Referring to this circle, you can see that the compensated stitches stick out beyond its true edges, the idea being that they will move in to the correct position during sewing due to the pull forces. Also notice that the compensation is greater at the widest portion of the circle than anywhere else. That's because the pull forces increase with larger areas. Theoretically, when you sew this compensated version of the design, everything will line up perfectly.

Of course, when dealing with compensation, the amount applied varies with different fabrics, so edits may have to be made if the design ends up on denim rather than fleece or vice versa.

One other trick to consider is using a satin border instead of a run border. It obviously has more stitches and provides a much bolder look, but the width of the satin column provides a certain margin for error, which allows some shifting of the fill stitch without any noticeable visual degradation of the design.

So there you have it: a brief look at the primary stitch control factors. No matter how good your software program is, it's only a tool to get the job done. It's up to you to manage the tool such that you can wrangle out the best possible design each and every time.

Award-winning author and international speaker Jimmy Lamb, the director of training and education for Tajima USA Sales & Support by Hirsch, Hauppauge, N.Y., has more than 15 years embroidery experience. He is the author of The Embroidery Business Survival Guide and a frequent speaker at industry events and trade shows.

For more information or to comment on this article, e-mail Jimmy at jlamb@tajima-hirsch.com.

Click here to read Primary Stitch Control Factors, Part 1, which focuses on managing stitch length and density.

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