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The downside is that getting set up for stretching screens can require a considerable investment, both in equipment and training and screen stretching can divert precious resources from core operations like production and marketing.

Do you really have to go into screen stretching? Definitely not. Many very large and well-established screenprinters continue to rely on outside suppliers for all of their screens. It’s a judgment call whether or not a screen stretching operation makes sense for your screenprinting business. To help you make that decision you need information and these next few articles will take a look at what’s involved in building screens and setting up your own screen stretching department.

The importance of screens
It is almost impossible to overemphasize the importance of screens. They are truly the heart of any screenprinting business. Screens impact everything from printing speed to registration. In fact, they affect so many of the variables in screenprinting that by making sure your screens are in top condition to begin with you can eliminate a host of potential problems later on. Good screens allow you to tackle the most technically demanding jobs with confidence. Good screens help you produce good work, so if you plan on building your own screens, make sure you build good ones.

What stretching your own screens can do for you
There is no question that the ability to stretch your own screens can bring you considerable advantages. Let’s take a look at a few of them.

You’re in the middle of an important production run and your screen rips. Normally, you have one or two backup screens available, but this time you don’t. If your shop doesn’t have the ability to stretch frames, you have few options other than to ship the frame back to your screen stretching supplier as rapidly as possible and wait for him to re-stretch it and return it. Depending on your distance from the supplier and his production schedule, several days may pass before you can get that screen back on the press. With your own in-house screen stretching operation that screen can be back on the press in a matter of hours. How much would that be worth to you?

Flexibility
A brand new customer walks in the door. He has a large order he would like to place with your firm. The only catch is he needs it right away and it requires a mesh count that doesn’t match any of the screens in your inventory. Do you (A) accept the job with confidence knowing you have your own screen stretching system that can produce top quality screens on short notice? Or (B) pick up the phone and desperately try to get your supplier to send you a new screen, or re-stretch one of your old frames in time to meet the deadline? If you can stretch your own screens that problem goes away. The ability to stretch your own screens can be a valuable resource that can enable you to take your business in new directions and adapt to changing market conditions.

Improved quality control
Stretching your own screens gives you much greater control over screen quality. And since screen quality affects so many factors in screenprinting, this can have an immediate and dramatic impact on the quality of your overall print production.

This becomes increasingly important as you take on more technically demanding print jobs such as four-color process printing. Successful four-color process printing requires four screens with identical mesh (thread count and thread diameter) stretched to identical tensions. An in-house screen stretching operation allows you to easily meet such specifications. This can also help improve print quality even in less critical jobs, because you can make sure your all screens are stretched with the correct mesh for the job and that mesh is always at the right tension.

Screens, if handled carefully, can produce many thousands of impressions. However, mesh is subject to wear. It wears a little every time a squeegee passes over it. As mesh wears it loses tension, and at some point every screen will lose so much tension that print quality will begin to deteriorate. A busy screenprinting operation can wear out a lot of screens. At some point it becomes more cost-effective for that screenprinter to stretch his own screens rather than shipping them out. The savings on shipping costs alone could be a significant factor.

Who should not do screen building?: Beginners
Unfortunately, it’s not the experienced screenprinter but the beginner who often wants to plunge into building screens. In fact, many newcomers to screenprinting seem to feel that building screens is the place to start. It’s understandable. Screens cost money and building your own screens seems like an easy way to keep down startup costs. Furthermore, screens look they would be easy to build, just a piece of fabric stretched over a rigid frame. And when it comes to frames, many frames are still built of wood and putting together a wooden frame appears to be something well within the capabilities of anyone with average carpentry skills. As for stretching mesh, at first glance that looks like something that someone with a pair of pliers and sufficient arm strength could manage.

Unfortunately for them, screens may appear simple, but they are also critically important to a screenprinting business and building a good screen is a technically demanding job that few beginners could accomplish. Of course, if someone were prepared to invest in the specialized equipment needed to stretch screens and put sufficient time and money into training, they could certainly do it. But if that person's objective is to become a screenprinter, he or she would be better off pulling prints or going out in search of new jobs than stretching screens. For someone just starting out, stretching screens is not a good way to save money.

Problem number one: Mesh tension presents challenges
Frames are the first problem. One of the key differences between a screen that will produce good work and one that will produce nothing more than problems is mesh tension. Frame strength has become increasingly important as mesh tensions have increased over the years. In the early days of screenprinting, printers were content to use screens tensioned so low they would not even register on many tension meters.

Today, screenprinters are often reluctant to work with mesh tensioned at less than 20 newtons per centimeter (20 N/cm). Mesh tension is expressed in units of measurement called newtons, a unit of force in the SI [mks] system. A screen frame holding mesh at 20N/cm has to be able to withstand a force of about 6.85 lbs. per linear foot, which means even a modest-sized screen holds enough tension to rip a poorly made frame apart.

Effects of weak frames
The effects of tension can often be seen in the tendency of longer frame members to bow inwards at the midpoint. The frames in many larger screens will bow inward to some degree, but weak frames will bow inward dramatically. Some may not be anywhere near adequate working tension and the tension they do hold they may not retain for very long.

Tension can also cause warping or twisting in weak frames. These frames can no longer allow lie flat, which means the mesh they contain cannot contact the surface of the substrate evenly. It is all but impossible to produce a good print with a screen that has a warped frame.

Even higher mesh tensions
Mesh manufacturers often recommend tensions that vary by a few newtons depending on the thread count and thread diameter of a specific mesh. Today, some of these recommended tensions are in excess of 20 N/cm. A few screenprinters prefer to exceed these specs even higher mesh tensions because higher tensioned screens generally produce better print quality, fewer registration problems, and faster production speeds. This has produced a consequent demand for stronger and stronger frames and a revolution in frame materials. If you would like to learn more about mesh tensions see an earlier article by this writer: Mesh Part II The Tension Rises (available on this site).

Frame materials: Wood
Over the history of screenprinting, frames have been made of a variety of materials including wood, plastic, steel, and aluminum. Wood was the first and continues to be popular. Light, cheap, and easily cut to any length, wood allows a screen builder to quickly assemble frames to accommodate the job in hand. Because wood has been a relatively inexpensive frame material it has allowed screenprinters to build a substantial inventory of screens in a wide variety of sizes. Although it is also the least durable of frame materials, a well-built frame made from premium-grade knot-free wood can last many years. Furthermore, it remains the only practical material for building frames in-house.

However, wood is also very weak. It tends to flex under pressure and as higher mesh tensions have become more popular, stronger materials such as steel or aluminum have gradually

Wood also tends to warp as it absorbs moisture and unfortunately, screenprinting frames spend a good part of their time soaking wet. Every time an exposed image is washed out or a screen goes through the reclaiming process, the frame undergoes a dousing, often at high pressure. Under such conditions, even the strongest wooden frame will deteriorate.

Why aluminum has become the material of choice
Water has also limited the use of steel as a frame material. Steel rusts rapidly in wet environments, so steel frames have to be protected with a coat of rust-inhibiting paint. The most popular frame material in use today is aluminum, which is unaffected by water. Much stronger than wood yet lighter than steel, aluminum quickly became the material of choice for larger frames. But its durability has gradually made it the material of choice for frames of all sizes. Aluminum frames may cost more than wood, but higher initial costs will be recovered over the lifetime of the frame.

Few screenprinting shops, however, are equipped to cut and weld aluminum. So, the popularity of aluminum as a frame material has led to the outsourcing of most frame building to specialists. If you decide to set up your own screen stretching operation, chances are you will be ordering frames from an outside supplier. Next time, we’ll take a look at some of the important specifications to keep in mind when ordering from an outside supplier as well as a few tips that may save you some money.