The ins and outs of manual printing

Labor of Love

Joe Clarke has spent the past 47 years in the lab and in the engineering department, in pre-press and on-press, as an R&D / technical researcher and as a manager of screen print production. Clarke has held executive positions as President of M&R Printing Equipment and as Vice-President at Wilflex [Poly One]. He has been granted a growing number of print-related patents, including one for High-Shear printing with Smilin'Jack - he is a member of the ASDPT, is an Associate Editor for NBM and an SGIA Fellow.

Clarke has presented hundreds of technical papers, written a couple books and published over 600 technical / management articles for which he has been awarded five Swormstedts; the international standard for excellence in technical writing.

Currently Joe Clarke is the President of CPR, a Chicago-based corporation which manufactures Synergy Inks including NexGen; environmentally & financially responsible T-Shirt inks. For more information on CPR, visit http://www.cprknowsjack.com/.

The manual press operator is a rare breed of creative-craftsman. With few exceptions, they will do anything necessary to ensure the highest-quality image imaginable. Then, by definition, the “best” manual press must be the one which allows the creation of these masterpieces quickly and consistently over a protracted lifespan.

But be forewarned: The press will only allow its operators to maximize the cumulative quality of the tools we bring to press if we add the unsustainable resource of time. So it seems the “best investment” must be the press that allows users to achieve our admirable goals is less time.

Quality-time continuum

To speak about the quality/time continuum, we’ll first need a common frame of reference. Consider what eats up so much time in preparation. There are only two time-eaters; the pair of perpetrators is dimensional image alignment (registration) and the art of balancing the ink thickness required by the mesh with the volume supplied by the blade.

Dimensional-image alignment is achieved with the use of a pair of adjustable bearings (hardened, eccentric cam followers) between which we wedge a steel bar every time we lower the screen. The other causes of mis-registration are the ability of the press to maintain parallelism between the screens and platens and the precision of the off-contact setting.

On top of this, we’ll require about 35 N/cm² printing tension to efficiently transfer even the nastiest white ink. Settings above the upper limit result in image displacement (an enlarged image in both directions). This is not to be confused with image drag in the stroke direction only, which is due to using single-axis, soft, buckled blades at low printing tension. Settings below the lower limit will cause image drag and other issues.

As the squeegee passes, the side-load on a typical 23" X 31" frame is about five pounds of pressure on every print stroke. This means we want a robust frame to be clamped into a robust side clamp which will not allow the frame to pivot (cantilever loading) or shift in reference to the image due to blade drag.

An observant print practitioner can garner almost as much information from the top of the screen as by looking at the printed image. The image on the right shows the result of blade buckling—the mesh is not completely cleared, there is excess white ink on the non-image areas and the ink trailed behind the blade. The solution is to reduce the initial angle shown in the image below so it clears, is clean on top and leaves no trails.

Microcosm of confusion

It’s important to realize that micro-register adjustments will not ever compensate for a shape change caused by drag and stretch. Micro can only move the shape. If drag and stretch have contorted a rectangle into a slice of white bread, it’s too late for micro! If the press won’t maintain parallelism and precision gap, the shape of the image will change and a millennium of micro adjustments won’t find a fit.

Now that we realize the difference in shift and shape, most micros operate not on an X and Y axis but an X1, X2 and Theta axis.

X1 and X2 push or pull from a position proximate to the corner of the screen frame. Independently, they pivot the screen in an arc. Turn both X1 and X2 simultaneously in the same direction and the frame will shift in the Y direction (north/south). The single Theta (an arbitrary angle near east/west) does not guarantee it will move the screen parallel OR perpendicular to our image, but it will shift the image.

If the bolts used for micro-adjust are 16-thread, every full turn of the knob will move the screen 1/16th of an inch—a window of registration we could drive a truck through. A quarter turn of the same knob will move the screen 0.015", or about the gauge of a thin credit card.

The best micro adjustments will have the finest threads to allow some combination of half or full turns (180 to 360 degrees) only slightly move the screens. Micro should reduce your effort, not test your eye-to-hand coordination.

Clamping situation

To ensure stability during the press run, look for large, wide, side clamps with double lock-knobs. The large surface area on the underside of the frame and two clamps per side will grip the frame, keep it from pivoting and shifting under the stress of printing tension, and drag if using a single-hinge blade. If using a round-tube frame, be certain to use the optional clamp adapters or buy a press with built-in adapters.

Most presses offer adjustable clamps to accommodate smaller-sized frames as standard equipment. We don’t want to make too much of this double-edged sword for it is always preferable to use the maximum screen size in order to minimize the resistance differential of the mesh during the print stroke.

The resistance differential is the reality that, when mesh is tensioned with a meter, the center of the mesh is most elastic and the perimeter is the least elastic. As we print closer and closer, this resistance increases and, as important, the ratio of minimum to maximum resistance increases. The resistance differential leads to variance in drag, opacity, transparency and color.

Finally, a “speed-table”—a setup where one person loads and unloads, allowing the operator exclusively to print—dramatically improves our labor-to-revenue ratios. But note there is no speed or table that will overcome the insurmountable loss of time due to poor parallelism, imprecise gap or unsecure clamping.

Study session

It is very unlikely any press will ever improve upon the potential of the tools with which we come prepared to print. But, invariably, the press can make things worse. Do homework up front, remember the value of parallelism and precision gap and differentiate between those facets attributable to the press or not. Happy printing!