Dr. Anderson's sage advice still rings true today with this flashback to 2003.
On the downside, moving the clamps, sideways can introduce several new problems. First, moving the clamps laterally has the effect of reducing the mesh count by spreading the mesh threads over a greater distance. If the threads ended up evenly distributed, this would not be an issue. However, lateral movement creates uneven thread distributions. The main concern is that mesh secured by the clamps is held at a fixed thread count, but the mesh between the clamps is not fixed, so, as the clamps move apart, the unfixed mesh experiences a drop in tread count. Because the bowing of the fibers is greatest at the edges of the mesh, this is where you find the most lateral movement of the clamps and variance in thread counts.
However, the mesh at the edges of the frame is not normally used to carry the printing image – the image areas of the stencil are usually centered on the screen. So any thread count changes that come from stretching with laterally moving clamps tend to have minimal effects on the printed image. The only cases in which this condition might impact the image is when large, continuous-tone elements are placed near the screen edges. In these situations, you’ll see narrow bands that represent changes in ink coverage caused by the larger mesh openings or possibly by loss of parts of the stencil.
To assist in further diminishing this effect, you can use a greater number of smaller clamps, which would allow better distribution of tension forces through many smaller lateral motions, instead of just a few large ones. More clamps mean that each clamp will be lighter, move sideways more easily, distribute the sideways movement more easily, and cause less variations in the mesh counts between the clamped and unclamped mesh threads. Smaller clamps also allow greater flexibility and interchangeability for different frame sizes. So, although single-clamps systems fix the mesh count across the width of the frame, they also produce greater tension-loss properties due to fiber realignment. Using multiple smaller clamps that allow lateral motion provides a superior solution.
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