The type of machinery used, and the parameters used to set up printing equipment, can have dramatic affects on both quality and efficiency in the printing plant. The printing equipment, whether manual or automatic, should posses certain attributes and adjustments.
This month, we’ll take a close look at manual screen-printing equipment. If you are ready to make a purchase in this category—and what could make you more ready than perusing the various equipment reviews on the following pages?—there are several key points to evaluate when comparing models. Take these into consideration before you buy, and your new press will have a much greater chance of serving your needs today and into the future.
By “registration,” I am referring here to the method or apparatus used to align one printing screen to the next—your multi-color press’s primary function. There are several methods employed for color-to-color registration in manual equipment. Manual presses, sometimes referred to as hand printers, are usually fitted with one of three types of registration systems, these include:
Adjustable steel ball bearings: In this type of system, each screen-support arm is fitted with a hardened-steel “keel” or bar. This bar is trapped between two hardened-steel ball bearings as the print arm is lowered into position. These bearings often have side-to-side adjustments to allow them to be tightened on the keel as the materials wear. (See Figure 1.)
Nylon bolts: This system operates similarly to the aforementioned set-up, with the screen-support arms being trapped between two nylon bolts when lowered into print position. These bolts can be adjusted in and out, as necessary, to apply appropriate tension on the arms.
“Roller-skate” wheels: Plastic wheels are employed in some less-expensive printers as a kind of hybrid between the ball-bearing and nylon-bolt systems.While all the above systems can provide adequate registration for general printing, my preference lies with the steel-ball-bearing system when registration is critical. Nylon bolts can also produce adequate results when properly adjusted, but are more subject to wear over time than their steel counterparts. For heavy or high-tolerance production, I would have second thoughts about a machine that employs parts not specifically designed for industrial use in an area as critical as print registration.
Another area that can affect the registration capabilities of manual-printing equipment is the employment of side screen holders. I am referring to a system that clamps the screens from both sides, as opposed to the rear of the frame. These side clamps will add stability to any type of screen, but are particularly important when utilizing wooden frames. Wooden frames have a tendency to flex in the corners, negatively affecting the print’s color-to-color registration. Side supports provide far more rigidity to the corners, producing superior register.To test this theory for yourself, take any frame—wood or metal—grasp it with your hands by one end frame member, and ask someone to wiggle the frame from side to side while you hold on as firmly as you can. Your ability to stop the movement will be limited, at best. Now take the same frame, grasp it from the sides and repeat the test. You will observe far more control over the process using the “side-support” method. Rear clamps are often offered as a less expensive alternative, and they are. They’re also considered, by some, to be slightly easier to use. However, as with most things in life, there are trade-offs. Depending on the nature of your work, I strongly recommend that you seek a configuration that will give you the best mix of maximum stability and ease of use.
The gap between the printing screen and the shirt or other substrate—with the screen in print position, but with no squeegee pressure applied—can play an important role in the quality of the finished print. Many people wonder, “What is the correct amount of off-contact?” Correct off-contact distance is determined by, and the product of, several other control variables. The goal, whether printing manually or automatically, is to allow the screen mesh to peal away from the substrate directly following the squeegee as it travels. This will allow the screen to be fully separated from the substrate before the print arm or head lifts. Off-contact distance is affected by:
- Screen tension—Inadequately tensioned screens will require far more off contact distance to affect a proper rate of peel.
- Ink viscosity—The thicker the ink, the more off-contact distance will be needed to provide a clean peel.
- Squeegee speed—If the squeegee is moving too quickly, you will require either more off-contact, or a tighter screen to achieve the desired peel. In this scenario, excessive off-contact can adversely affect print registration; increasing screen tension is recommended. Highly tensioned screens not only require less off-contact distance, but can also be run at higher print speeds, potentially increasing yields.
- Garment weight—The garment weight or thickness (as in the difference between a T-shirt and a sweatshirt) will, of course, affect the appropriate off-contact distance.
Historically, off-contact was achieved on most presses with the addition of shims—ie: paint stir sticks, washers, coins, etc.—placed on the platen, beneath the frame. Many manual printers now available offer off-contact adjustment mechanisms. (See area circled in blue, Figure 2.)
A critical feature that is often overlooked with such a configuration is its ability to keep the screen parallel to the platen when off-contact is increased or decreased. Some systems increase off-contact distance by tilting the screen upwards; this, however, will cause uneven off-contact across the length of the screen, and should be avoided.
Regardless of the type of printer, it is critical that all platens be level and adjusted to exactly the same height and plane, parallel to the screens in their print position. This becomes increasingly important as print difficulty increases. If even one platen or its support arm are out of level, unwanted light or dark areas may show up on the printed substrate. This affect will be particularly pronounced when printing process work.When selecting a manual press, therefore, an important consideration is your ability to adjust the level of the platens. In Figure 3, you can see three leveling bolts mounted to the bottom of the platen support arm. For adequate platen-level adjustability, look for a configuration that accomplishes this objective.
One final consideration when researching manual screen-printing presses is the manufacturer in whom you’ll be placing your trust. Be sure you are dealing with a solid company that has a history and good reputation in our industry. It is critical that they will be there to support and back-up your purchase.