How to Determine a True Thread Break

Minimize production interruptions by knowing the difference between thread breaks, thread pull-outs and false thread breaks. January 25, 2011
By Frank Gawronski, Contributing Writer

This is an example of thread pulled out of the eye of the needle. Note how clean the end of the thread is.

Operating a computerized embroidery machine can be a very rewarding experience and career. Making a design come to life one color at a time is a mesmerizing mirage to the novice and signals the closure of a work order to others. No matter how you look at it, converting a “blank” item into a “finished,” marketable garment generates a unique sense of fulfillment. Even occasional interruptions, such as thread breaks, don’t seem to dampen that spirit. But when the interruptions reach a level that threatens the reservoir of good will found in each of us, that euphoria often changes to frustration — or worse.

By its nature — and the complexity of the process — thread inevitably will break on occasion. This triggers a chain reaction that stops the embroidery machine and signals the operator with either a still or flashing red light over the embroidery head that is experiencing the problem. This is accepted as part of the operator’s job; simply re-thread the needle, back up to mend when necessary and continue with the sewout.

Sometimes this thread break is just a fluke that indicates an adjustment may be necessary. Other times, it may not be a thread break at all. In this article, I’ll explore the machine signals, what they mean and the actions you can take to minimize these interruptions.

The Signals
Embroidery machine manufacturers have been using low-voltage electronic signaling to indicate thread breakage for several decades. Until recently, this was accomplished with a primitive switching system that used the check spring as the switch and a logic board, which was usually equipped with a red light and an on/off switch. When the upper thread breaks, the check spring grounds itself, thus stopping the machine and illuminating a red lamp that normally is unlit.

As the technology developed, equipment makers began to add under-thread sensors, using more sophisticated strain gauges and electronic “eyes” to read the bobbin thread. When automatic thread trimmers were first developed, the quest for an under-thread sensing system was temporarily discontinued because they occupied the same physical space on the machine.

Today, everything has changed. Instead of using the check spring as a switch, many machine manufacturers are metering the flow of the thread from the top of the machine with optical encoders to determine upper thread activity, as well as bobbin condition. With LED technology, the old “red light for thread break” notification method has changed to include a multilevel lighting scheme. With this new technology, no light means “head off,” a green light means “head operational,” a red light means “upper thread break,” and a flashing red light means “bobbin out.”

In spite of this technology, the machine still does not know how to distinguish between a legitimate thread break, a thread pull-out and a false thread break. It is up to the operator to make this determination and take the appropriate corrective action.

Not All Breaks Are The Same
As you can see, embroidery machines are programmed to illuminate a particular signal to the operator when a problem exists. For example, we assume an illuminated light means the thread has broken in production. However, in practice, there are two other times when thread-break conditions can be met with no thread actually having been broken. The occurrence and frequency of these exceptions will depend on the mechanical condition of the machine and the appropriate syntax found in the designs.

The first exception, which is very common and registers the same signal as a regular thread break, is a thread pull-out. The difference is subtle; however, the resolution may be drastically different. This is why the operator has to learn the difference between a thread break and a thread pull-out.

A regular thread break can happen anywhere in a design, regardless of the stitches being rendered. A thread pull-out, on the other hand, only occurs when the machine is attempting to start after a trim. It may occur during the inching stitches or shortly after the machine kicks into high gear.

The second exceptional phenomenon is a false thread break. It can occur anytime during the stitching process and can be easily identified. This is because even after the machine has stopped and the light is lit, the thread is still threaded through the needle and connected to the embroidery in process.

Corrective Action
There are many causes for thread breaks, pull-outs and false thread breaks. Some of these causes may be unique, while others are shared. This is why it is better to first diagnose the type of thread break before considering the applicable causes.

• Thread Breaks: A legitimate thread break can occur anywhere in a design. It usually is an indication of excessive stress, abrasion or tension on the thread. Bobbin thread tension should be set at about 25 grams, while the top thread tension should be set between 100 grams and 140 grams for rayon thread or between 110 grams and 150 grams for polyester thread. These ranges vary with the thickness, density and composition of the fabric being sewn.

In addition to tension, other causes for repeated thread breaks could include: a bad needle, improper hook timing, improper needle depth, a burr or rough edge on the contact surface of the needle plate, presser foot or even rotary hook.

• Thread Pull-Outs: A thread pull-out looks exactly like a thread break. The thread is out of the eye of the needle and the machine stops to signal a thread break. The difference between a thread pull-out and a break is that rather than breaking, the thread simply pulled out of the eye of the needle at startup. Usually, this indicates a tension and/or thread trimmer problem. It is easy to diagnose, since it always happens when the machine attempts a startup after a trim.

Three areas could be the cause of thread pull-outs: the design, thread tensions and trimmer mechanism. First, all designs must include proper syntax for thread trimmers. This syntax includes lock-off stitches, a trim trigger (i.e. color change, end of design code or three consecutive jump stitches) and lock-on stitches. Most digitizing software will do these automatically if the feature is turned on, is configured correctly and the digitizer controls all trims. This means the digitizer has to use the trim command for all trims and not let the machine do any trims by default.

Next, if the thread tensions are not set correctly, you may experience a lot of thread pull-outs. If the upper thread tension is too loose, the knives may not cut properly, and you probably will have a lot of bird’s nests. If the upper tension is too tight, the tail will cut too short, resulting in thread pull-outs. If the bobbin tension is too tight, the bobbin tail will cut too short and you also will experience the problem.

The trimmer mechanism also may come into play when assessing a thread pull-out. Mechanically, there are three basic trimmer parts: the picker, cutting knives and upper thread hook.

The picker forms a triangular loop with the upper thread that enables the moving knife to select the proper threads for cutting. The moving knife usually begins its stroke at 60 degrees before the top of the needle bar stroke, and then releases 60 degrees after. The upper thread hook then grabs the cut thread and lays it against a holding bar that is often covered with a self fastener.

As you can see, the trim cam has to be set correctly; the picker has to be angled and set correctly; the knives have to be meshed and indexed correctly; and the upper thread hook has to be angled, indexed and height-adjusted so it does not apply excessive pressure against the self-fastener thread holders.

It is best to contact a trained technician when adjusting trimmer parts. The settings are fastidious. Without the proper training and patience, the credence of trimmer technology may be hard to sustain.

• False Thread Breaks: When false thread breaks occur, the machine is really registering a false alarm. Since the thread is not broken, the machine can be immediately started and will continue to sew normally.

On an older machine style that uses the check spring to detect thread breaks, this usually means that the thread tension is too loose at the pre-tensioner or the thread path may be wrong. Another common cause is a check spring that is adjusted too tightly. The check spring only should be loaded with 1⁄8 to 1⁄4 turn past the point when contact is made against the check spring stop.

On a newer machine, this could be caused by improper thread tension or thread path. Additional reasons might be a maladjusted encoder index finger, an electrical short or possibly a bad circuit board.

With a little practice, you can diagnose pesky thread break issues and get their frequency under control. After all, it’s not the size of the orders or the stitch counts that make you money, it’s the limited amount of down time that fattens your bottom line.

Frank Gawronski is a speaker, writer and consultant who started in the embroidery industry in 1975. He founded Embroidery Educational Services Intl., an independent embroidery training and consulting firm, in 1988. For more information or to comment on this article, e-mail Frank at frankg@embroideryedu.com.



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