Primary Stitch Control Factors, Part 1

Stitch length, density and underlay all impact embroidery quality. In Part 1 of a two-part series, learn how to correctly manage stitch length and density.
Feb 1, 2008

Long stitch settings will make a curve look jagged (left), so use shorter stitch lengths for curved runs (right) and make up the extra stitches by using longer stitch lengths for straight segments.

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 letting the software make the decisions instead of experimenting 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 — 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. All of these factors apply to satins and fills, but stitch length is the only factor involved when working with runs and manuals.

STITCH LENGTH
Stitch length is of extreme importance and can be a major limiting factor for sewing. It takes two needle penetrations to create one stitch. If the penetrations are too close together, the result is a hole instead of a stitch, which leads to poor quality-sewing and numerous thread breaks.

On the other hand, stitches that are too long tend to be fragile and weak. They are easy to "snag" and pull out of the finished embroidery. In addition, long stitches don't sew well and tend to pull the bobbin thread to the top.

For run stitches, stitch length is the distance between each needle penetration. That's obvious. But what may not be so obvious is how stitch length affects the appearance and performance of the design. Though it's tempting to use the default settings, you need to experiment to find out what works best for each application.

For example, a curved run stitch with a stitch length set too long may not appear as a true curve but as a series of straight lines. By shortening the stitch length, you can get a smoother appearance, but you'll also increase the overall stitch count. As a general rule, depending on the fabric, try to go with higher stitch length settings for straight segments to keep stitch counts down, while using lower settings for curves to keep them looking round and neat.

Stitch lengths also affect satins and fills. For satins, stitch length refers to column width. When dealing with fills, the stitch lengths of individual stitches within the segment can be manipulated in order to create interesting patterns and special effects.

DENSITY
Proper use of density can create different visual affects, whereas improper use can affect both quality and performance. For example, too much density causes fabric puckering, and too little density lets the fabric show through the top stitches. In addition, excessive density can result in thread and needle breaks. As a general rule of thumb, as the design gets smaller, density is decreased; as it gets larger, density is increased. But with higher density also comes the need for increased underlay in order to reduce puckering.

Another factor that can affect density settings is color. When the color of the thread is in great contrast to the color of the garment, such as white thread on a black shirt, the color of the fabric will be more likely to show through the stitches. A moderate increase in density is justified, but be careful not to go overboard. Too much density won't necessarily solve the visual issue and will lead to performance problems.

Much like painting, sometimes it's better to use two thin coats rather than one thick one. Instead of trying to double the density setting, consider using two layers of thread at angles to each other to prevent color show-through.

An interesting aspect of density is that most embroiderers don't really understand the numbers and may end up selecting values that their machine can't physically sew. That doesn't mean the machine won't run: It just means that the quality of the stitching may be slightly off.

Like it or not, a digitized design is a set of precise instructions that tell the machine what to do. Since all machines are calibrated in metric values, the data has to be delivered in a metric format, yet most American embroiderers still use the (English) imperial system of stitches per inch (spi) instead of the metric system of points and/or millimeters.

For stitches per inch, the density measurement refers to the number of stitches in a linear inch. If you have a satin stitch with a density of 63.5 spi, there are 63.5 stitches, laid side by side, in one linear inch.

For points (pt), density is a measurement of the distance between stitches, measured at the endpoints. To convert between the two systems, use the following formulas:

Are you confused yet? Luckily, the digitizing system makes the conversions for you, but that doesn't mean you should trust the software.

Just because you can program it doesn't mean the machine can sew it. The motors that drive the pantographs on most modern commercial embroidery machines are calibrated to move in increments as small as 0.1 mm (one decimal place). However, a number like 0.12 mm (two decimal places) is too precise for such a machine, so the software will adjust the stitch spacing to average this setting, which means unequal spacing between stitches.

It just so happens that 4 pts (0.4 mm) of density is considered the ideal density for most applications. But let's say you wanted to decrease the density slightly to 4.3 pts (0.43 mm). Easy enough, just type the value in.

Unfortunately, the density setting of 4.3 pts is too precise for the machine to sew, thus density will have to be averaged as shown in the drawing above.

Each diagram shows one side of a satin stitch that has been zoomed in so that you can see the individual stitches and the distance between them. If you count the spacing in the diagram on the left, you will see that each stitch is separated equally by a distance of 0.4 mm or 4.0 pts (the grids are set at 0.1 mm x 0.1 mm).

However, in the diagram on the right, the distance between the first two stitches is 0.4 mm, while the distance between the second and third stitches is 0.5 mm. Notice the repeating pattern. Also notice the inconsistent spacing, which leads to inconsistent stitch lengths.

With many designs, this will not be a huge factor, so don't lose any sleep over it. However, when working with fine details and small satin letters, the quality can be affected by improper density settings. Thus, the digitizer should be careful to use the correct settings.

By the way, the 4.3 pst value used in this example is equivalent to 60 spi, which seems to be a nice round number. It just goes to show that when you randomly choose numbers without understanding the result, you may not get what you bargained for.

A good way to get comfortable with density settings is to create a chart of 1-inch square fills with different densities so that you have a simple visual reference. When working with different materials, sew this chart on the fabric to see how the different densities look and react to that particular fabric.

Underlay, the third stitch control factor, is probably the most important aspect of any design, yet it remains invisible in the finished product. In next month's issue, we'll take a very close look at how this invisible item impacts your embroidery.

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.

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