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Squeegees: How to Use Them - Part 1: Setting Up
Pulling a squeegee is a skill that develops over time. The ability to control pressure, speed, and angle during a print stroke belongs to that class of knowledge described as muscle memory or feel. The art of creating perfect prints every time is largely the result of pulling many prints and closely examining the results.
Mesh Tension: The force that pushes back
We know the first part of the printing process begins with the squeegee forcing the mesh down against the substrate. The squeegee then moves forward across the screen pushing before it a wave of ink known as the working head of ink.
Only one small portion of the mesh, a narrow line of fabric directly underneath the leading edge of the squeegee blade, comes into contact with the substrate at any one time. Before the edge of the squeegee arrives at a given point, the tension in the mesh keeps the mesh suspended above the surface of the substrate. Immediately after the blade passes, the tension raises the mesh off the surface again. This rapid snap-off of the mesh is essential to creating a clean and unsmeared imprint. Without this effect most types of screenprinting simply won't work.
There is no standard off-contact distance. It really depends on the size of the screen, the tension in the mesh, and preferences of the individual printer. The best off-contact distance is almost always the smallest that you can get away with.
Over the years handprinters have devised ingenious systems for setting off-contact distances, the least complicated being to attach shims to the underside of the frame with tape. Another popular method is to drive screws into the underside of the frame, allowing off-contact distance to be adjusted with a few turns of a screwdriver.
Whatever the distance, it should be equal at every point. Ideally, the screen will be level. When you gain some experience setting off-contact distances, an eyeball measurement should be sufficient, but you might find it easier to actually measure the distance for your first few set-ups.
The more highly tensioned the screen, the closer it can be positioned to the substrate. This is one reason why new screens print better than old ones and professionally made screens tend to work better than homemade ones. It's all a matter of tension. It takes far less downward pressure on the squeegee to close minimal off-contact distances than it does to close the large gaps necessary to compensate for under-tensioned screens.
The only way to print with a screen that has lost most of its tension is to exaggerate the off-contact distance. This allows the downward pressure on the squeegee to create enough tension in the mesh to make it snap off of the substrate. Of course, this means the printer has to work much harder, and the extra pressure generates extra wear and tear on the squeegee, the stencil, and even on the mesh. Admittedly, this is not much of a problem where the mesh is concerned; it's probably ready for the garbage can anyway.
Unfortunately, the tension created by large off-contact distances tends to be uneven. In any screen the mesh near the frame tends to be less flexible than the mesh in the middle. In a low-tension screen set at a large off-contact distance this effect is magnified, so that the ends of the squeegee have to work harder than its midsection.
Get a grip (How to hold a squeegee)
In the standard grip, sometimes called the pinch grip, the printer places both hands palm down on top of the squeegee handle and grasps it between his fingers and thumbs. The hands are placed far enough apart to apply equal pressure along the entire length of the squeegee. A few printers prefer alternate grips. What matters most is that the grip you use is comfortable for you.
In fact, the standard squeegee grip may not be ideal. Many printers complain of pain in their hands and forearms following long print runs. NIOSH (National Institute for Occupational Safety and Health) studies have found problems with both the pinch grip and the width of the standard squeegee handle. NIOSH recommends using a handle that's 18% wider than the standard handle. An alternative to replacing all of your standard squeegee handles would be to pad them with a compressible material to allow for a more open grip. There are now on the market a number of ergonomically designed alternatives to the standard squeegee handle, and it may be worth your while to investigate some of these. After all, you're the one that's going to be pulling all those thousands of prints.
A good rule is to use no more pressure than the minimum required to produce a successful print. A great many printers use only enough downward force to close the off-contact distance. This is usually sufficient. If you can feel the blade bend, you're overdoing it.
Too much force exerted on the squeegee can not only prove tiring, it can be a contributing factor to repetitive stress injuries. It's also a major contributing factor to wear and tear on stencils, screens, and squeegees.
Excessive pressure can also lead to messed-up prints, especially if screens are at less than optimum tension. A heavy hand on the squeegee can actually drag the mesh slightly in the direction of the print stroke. When the mesh moves, the stencil moves with it, enlarging the printing areas and shifting the printed image enough to cause registration problems.
The solid areas of the stencil also move, dropping part of the non-printing area into newly deposited wet ink. On subsequent prints, this wet ink is transferred to the substrate leaving a faint outline shadowing parts of the image, a phenomenon known as ghosting. This misplaced ink will appear on every subsequent print until it either wears off on substrate or the printer stops and wipes it off the bottom of the screen.
Squeegee angle is really a matter of preference, which varies considerably from printer to printer. Factors specific to the job at hand also help determine squeegee angle: the type of ink, mesh count, substrate, and squeegee durometer. The most important factor of all is ink deposit.
If you think of a squeegee blade with the blunt end of the blade being pressed straight down on the screen as being at 90 degrees, the closer you hold your squeegee to the 90 degree position the less ink it will lay down. Conversely, the sharper the angle of the blade to the screen, the greater the ink deposit. Hold the squeegee too nearly vertical or angled too far over and it will not print effectively. Most printers hold their squeegees at a squeegee angle somewhere between 65 and 75 degrees off the screen, that is tilted about 15 to 25 degrees from the vertical position.
With an automatic press you can set the squeegee angle very precisely. The holding mechanism will also maintain whatever angle you select from print to print. In hand printing, however, consistency can be a problem. The printer sets the angle all over again with every pull of the squeegee.
The pressure the printer applies to the squeegee can also have some effect on ink deposit. The term squeegee angle refers to the angle the blade makes with the screen before any pressure is applied. But blades are flexible and even a modest amount of pressure will cause even the higher durometer blades to flex slightly. This effectively changes the angle of the blade in relation to the screen. This angle formed by the blade under pressure is called the effective angle or the angle of attack. Strictly speaking, it's the angle of attack, not the squeegee angle that determines the ink deposit.
For example, if all other factors remain the same, a lower-durometer blade will tend to leave a heavier ink deposit than a blade of higher durometer. The reason is that the lower-durometer blade bends more under pressure creating a sharper angle of attack. This sharper angle generates additional downward force on the ink, which tends to leave a heavier ink deposit.
Printers usually think of squeegee angle as the factor that controls ink deposit, because the angle of attack is difficult to see and almost impossible to measure -- particularly by the person pulling the print. It's easy enough to adjust the squeegee angle and the pressure used during a print stroke. In fact it can be done at any time during a print run, allowing the printer to make adjustments to ink deposit based on the appearance of the previous print.
The only other methods of controlling ink deposit, like changing to a different mesh count or using additives to change the viscosity of the ink, have to take place before the print run begins.
The first few prints
Assuming everything is working properly, it's now time to begin the actual print run.
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